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2017

2017.11.30: The paper "Star Scheduling Mode-A New Observing Strategy for Monitoring Weak Southern Radio Sources with the AuScope VLBI Array" by L. McCallum, K. Le Bail (61A/NVI), D. Mayer, M. Schartner, J. McCallum, J. Lovell, O. Titov, F. Shu, and S. Gulyaev was published in Publications of the Astronomical Society of Australia, 34. This paper discusses a new VLBI observing strategy, the star scheduling mode.
2017.09.15: Hana Krásná (TU Wien) made a presentation at the IAG meeting in Kobe, Japan: ''Correlated Atmosphere Noise in VLBI Analysis'', by Hana Krásná and John Gipson. She demonstrated that modeling station dependent measurement noise in the VieVs VLBI analysis software improves the repeatability of station positions and the agreement between VLBI and GPS determinations of Polar Motion. John Gipson had demonstrated the same effect in Solve, the Goddard VLBI software, in 2007, but the new study provides the first independent verification.
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2017.07.25: In his role as the International VLBI Service for Geodesy and Astrometry (IVS) Analysis Coordinator, John Gipson attended the Unified Analysis Workshop of the International Earth Rotation and Reference Systems Service (IERS), which was held in Paris from July 10 through July 12. Gipson chaired the VLBI session of the workshop. He made presentations on 1) relativity models in VLBI and 2) a model of diurnal and semi-diurnal Earth Orientation Parameter variation. He moderated the VLBI discussion and prepared a summary of recommendations for VLBI. Dan MacMillan also attended the IERS Unified Analysis Workshop. He was a representative of the VLBI geodetic technique and made presentations on VLBI reference frame scale systematics and on the effect of different mean rotation pole models on VLBI results.
2017.05.25: The GSFC VLBI group presented three talks and three posters at the 23rd Working Meeting of the European VLBI Group for Geodesy and Astrometry held May 15-19 in Gothenburg, Sweden. John Gipson and Karen Baver presented "Simulation Results for KOKEE12M-WETTZ13S Intensives". This talk presented the results of simulations designed to determine a good schedule configuration for VGOS (broadband) IVS-INT01 sessions. Ed Himwich, Alessandra Bertarini (Reichert GmbH, Germany), and Brian Corey (MIT Haystack, USA) presented "Impact of Station Clocks on UT1-TAI Estimates". An error in VLBI station clocks relative to UTC causes an error of the same size in UT1-TAI. This talk discussed the size of the effect, how measurements are made and how they are applied at the correlators, and the accuracy of the results. It also discussed future possibilities for the absolute determination of UT1-TAI. Karine Le Bail, David Gordon, Gipson, and Dan MacMillan presented "Investigating the Noise Floor of VLBI Source Positions". The authors studied the latest GSFC VLBI source time series solution and determined the noise floor per source using the Allan variance. Some sources reached a noise floor as low as five microarcsecs. Baver and Gipson presented "Reduction of the IVS-INT01 UT1 Formal Error through New Sked Algorithms". This poster presented the results of developing and applying two Sked scheduling program algorithms designed to improve temporal coverage or spatial coverage to three styles of INT01 schedules --- operational S/X, R&D S/X, and proposed VGOS schedules. Dirk Behrend, Cynthia Thomas, Gipson, and Himwich presented "Planning of the Continuous VLBI Campaign 2017 (CONT17)". This poster presented current plans for the 2017 15-day observing campaign, as well as the next steps in the preparation for the campaign. Finally, Sergei Bolotin, Baver, Gipson, Gordon, and MacMillan presented "Implementation of the vgosDb Format at the GSFC VLBI Analysis Center". This poster discussed plans for switching from VLBI's current data format (Mk4 databases) to the new, vgosDb format in routine VLBI data analysis. It also presented the utilities that will accomplish this and that will replace the current operational software.
2017.05.16: Four GSFC VLBI group members contributed to the 9th IVS Technical Operations Workshop (TOW) that was held at the MIT Haystack Observatory in Westford, Massachusetts from April 30 to May 4, 2017. Dirk Behrend organized the 9th IVS Technical Operations Workshop (TOW) together with staff from MIT Haystack Observatory. He was responsible for the overall program and class assignments. He chaired two sessions and moderated the teachers' meeting. Ed Himwich taught classes about four subjects: automated pointing models, Field System station software coding, the impact of operations on data analysis, and near term Field System plans. David Horsley trained VLBI operators in the TIG monitoring suite and Linux System administration. Karine Le Bail gave a science overview lecture that presented various results and applications derived from VLBI data.
2017.05.16: Dan MacMillan made a presentation, "Analysis of Polar Motion Differences between VLBI, GNSS and SLR", co-authored with Erricos Pavlis (UMBC), at the European Geosciences Union (EGU) General Assembly, which was held in Vienna, Austria, April 23-28. He also made a presentation at the IAG SC 1.4 meeting on work done in 2016 and 2017 by the IAG working group that he chairs about the impact of geophysical and astronomical modeling on reference frames and their consistency (working group 1.4.2).
2017.03.15: A paper written by Dan MacMillan, "EOP and Scale from Continuous VLBI Observing: CONT Campaigns to Future VGOS Networks," has been published by the Journal of Geodesy. This paper discusses 1) the precisions of CONT EOP and scale, which have improved by better than a factor of two since 2002 to the point where polar motion precision in the most recent CONTs is close to the level of GNSS precision, 2) the precision of the operational R1 and R4 sessions, which have substantially worse precision than CONTs, probably due to network inhomogeneities, and 3) simulations of broadband VGOS networks in 5 to 10 years that are expected to have 25 to 30 sites and to yield precisions about three times better than the latest CONTs.
2017.01.23: The latest official GSFC VLBI ITRF quarterly solution (2016a), quarterly intensive solution (2016a_int) and their associated earth orientation (eop) products can now be accessed through this web site's Data and Results page.
2017.01.06: Two members of the GSFC VLBI group contributed to three presentations at the 2016 Fall AGU meeting. Dirk Behrend (61A/NVI) gave an invited talk about the International VLBI Service for Geodesy and Astrometry, "IVS: Current Status and Future Plans". The talk focused on the capabilities of the legacy S/X VLBI system, which is currently used for creating IVS products, and the roll-out of the future VGOS VLBI system. Dan MacMillan (61A/NVI) and Erricos Pavlis (JCET/UMBC) presented a poster, "Analysis of Differences Between VLBI, GNSS, and SLR Earth Orientation Series". The poster discussed the precision of the three techniques and biases between pairs of the techniques, and it analyzed two weeks of data from May 2014, when the IVS held its most recent CONT (continuous observing) campaign. Erricos Pavlis, Daniel Koenig, and Magda Kuzmicz-Cieslak (JCET/UMBC) and Dan MacMillan (61A/NVI) presented a poster, "GGOS2020 Space Geodesy Network: Variations in System Deployment Scenarios". The poster discussed the results of simulation studies to determine the size and station density of the global space geodetic network of VLBI and SLR stations that will meet GGOS goals of 1 mm decadal accuracy and a temporal stability of 0.1 mm/yr.

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2016

2016.12.05: The Journal of Geodesy and Geoinformation has published "Comparison of VieVS and Solve UT1 Results from VLBI Measurements". This paper compares UT1 results from GSFC's Solve software package and the Vienna University of Technology's VieVS package. The first author is Minttu Uunila (Aalto University's Metsähovi Radio Observatory, Finland), and other authors are Karen Baver, John Gipson, Tobias Nilsson (GFZ German Research Center for Geosciences, Germany), and Hana Krásná (Vienna University of Technology, Austria). The paper is now available on-line here.
2016.10.24: David Horsley gave a presentation to members of the international VLBI community gathered at the MIT Haystack Observatory in Westford, Massachusetts, USA. The presentation demonstrated the current state of new operations monitoring software being developed and tested at the GGAO VLBI station. The talk resulted in stations from Australia and Spain offering their support of the project.
2016.10.07: Dirk Behrend is a co-author of a paper that has been accepted by the Journal of Geodesy: "International VLBI Service for Geodesy and Astrometry---Delivering High-Quality Products and Embarking on Observations of the Next Generation". Axel Nothnagel (University of Bonn) is the paper's first author, and Thomas Artz (University of Bonn) and Zinovy Malkin (Pulkovo University) are the other co-authors. The paper discusses the current operations of the International VLBI Service (IVS), as well as the service's outlook for realizing the VLBI Global Observing System. The paper places an emphasis on the IVS polar motion product because this product can be independently validated, and the paper compares IVS polar motion results to results from the International GNSS Service.
2016.10.07: A paper written by David Gordon, "Impact of the VLBA on Reference Frames and Earth Orientation Studies", has been accepted by the Journal of Geodesy. The paper examines how usage of the VLBA has improved the celestial reference frame, the terrestrial reference frame, and Earth orientation parameters.
2016.06.20: On Thursday, June 9, successful fringes were detected between the GGAO12m (Maryland), Westford (Massachusetts), Wettzell (Germany), and Yebes (Spain) VGOS stations for all four VGOS bands. This is the first observation of a transatlantic, four band VGOS baseline. People who contributed to this major accomplishment include Ed Himwich (NASA GSFC), Katie Pazamickas and Jay Redmond (GGAO), Mike Titus, Brian Corey, and Chet Ruszczyk (Haystack), Mike Poirier and Alex Burns (Westford), Alexander Neidhardt, Christian Ploetz, and Gerhard Kronschnabl (Wettzell), and Pablo de Vicente and Laura Barbas Calvo (Yebes).
2016.06.20: "Second Epoch VLBA Calibrator Survey Observations --- VCS-II" has been published in the Astronomical Journal (doi:10.3847/0004-6256/151/6/154).. David Gordon is the first author, and Chopo Ma is a co-author. The other authors are Christopher Jacobs (JPL), Anthony Beasley (NRAO), Alison Peck (NRAO), Ralph Gaume (USNO), Patrick Charlot (Laboratoire d'Astrophysique de Bordeaux, University of Bordeaux and CNRS) Alan Fey (USNO), Oleg Titov (Geosciences Australia), and David Boboltz (NSF).
2016.03.30: "Second Epoch VLBA Calibrator Survey Observations --- VCS-II" has been accepted for publication in the Astronomical Journal. David Gordon is the first author. The other authors are Christopher Jacobs (JPL), Anthony Beasley (NRAO), Alison Peck (NRAO), Ralph Gaume (USNO), Patrick Charlot (Laboratoire d'Astrophysique de Bordeaux, University of Bordeaux and CNRS) Alan Fey (USNO), Chopo Ma, Oleg Titov (Geosciences Australia), and David Boboltz (NSF).
2016.03.30: The GSFC VLBI group participated in the 9th IVS General Meeting, which was held in mid-March in Johannesburg, South Africa. The group gave the following five oral presentations. John Gipson presented "El Niño and VLBI Measured LOD". David Gordon and Karine Le Bail presented "Status of the X/S Source Catalog". Le Bail, Gordon, and Chopo Ma presented "Selecting Sources that Define a Stable Celestial Reference Frame with the Allan Variance". Ma, Dan MacMillan, Gordon, and Le Bail presented "Aspects of ICRF-3". MacMillan presented "Next Generation Global Geodetic Networks for GGOS" along with Erricos Pavlis, Magda Kuzmicz-Cieslak, and Daniel Koenig (all from UMBC).

The GSFC VLBI group also presented the following five posters. Dirk Behrend, Cynthia Thomas, and Ed Himwich presented "Implementation of the VGOS Trials". Sergei Bolotin, Gipson, MacMillan, Karen Baver, and Gordon presented "Transition to the vgosDb Data Format". Gipson and Baver presented "Improvement of the IVS-INT01 Sessions through Bayesian Estimation". Gordon presented "Difxcalc: Calc11 for the DiFX Correlator" along with Walter Brisken (NRAO) and Walter Max-Moerbeck (MPIfR). Thomas, Behrend, and MacMillan presented "From CONT to VGOS: The Evolution of the CONT Campaigns".

Group members also contributed to additional aspects of the General Meeting and its splinter meetings. Behrend, Gipson, and Himwich served on the General Meeting's Program Committee. In their capacities as IVS Directing Board members, Behrend, Gipson, Himwich, and Ma participated in the IVS Directing Board meeting. Gipson conducted the IVS Analysis Workshop, in his capacity as the IVS Analysis Coordinator. MacMillan chaired the meeting of the IVS Working Group on Galactic Aberration. Himwich taught a course about operations and pre-checks at the mini-TOW Workshop, along with Jonathan Quick (HartRAO). Finally, Gipson taught a course about scheduling VLBI sessions at the IVS VLBI School.

2016.02.09: The Space Geodesy Project team completed the integration of the broadband signal chain with the new 12 meter VLBI antenna at NASA's Kokee Park Geophysical Observatory (KPGO) in Hawaii. First light was seen through the system on February 1 with peaks observed on Taurus A, Orion and 3C84. Broadband fringes were detected on February 5 on all baselines using the KPGO 12-m and antennas at GGAO and Westford. Ed Himwich, who develops and maintains the VLBI field system software that controls most IVS antennas, is supporting this effort. Kokee 12-m antenna pointing upward with a small white and gray building with a window behind it and a line of trees behind the building.  An orange crane is extended over the top of the 
antenna, with two people standing in the crane's  basket.
2016.01.14: "IVS Observation of ICRF2-Gaia Transfer Sources" has been accepted for publication in the Astronomical Journal. This paper describes details and results of an IVS program that was set up to observe 195 ICRF2 sources in conjunction with the European Space Agency's Gaia mission for the purpose of aligning the ICRF2 radio-frequency celestial reference frame with the optical-frequency celestial reference frame being observed by Gaia. Karine Le Bail is the first author. Other authors include John Gipson, David Gordon, Daniel MacMillan, Dirk Behrend, Cynthia Thomas, Sergei Bolotin, Ed Himwich, Karen Baver, Brian Corey (MIT Haystack Observatory), Mike Titus (MIT Haystack Observatory), Géraldine Bourda (Observatoire de Bordeaux) Patrick Charlot (Observatoire de Bordeaux), and Arnaud Collioud (Observatoire de Bordeaux).

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2015

2015.12.22: The Journal of Geodesy and Geoinformation has accepted a paper written by first author Minttu Uunila (Metsähovi Observatory), Karen Baver, John Gipson, Tobias Nilsson (GFZ German Research Centre for Geosciences), and Hana Krásná (Vienna University of Technology). "Comparison of VieVS and Solve UT1 Results from VLBI Measurements" compares the estimation of UT1 by the Vienna University of Technology's VieVS software package and the GSFC VLBI Analysis Center's Solve software package using data from one hour and twenty-four hour IVS sessions.
2015.12.22: John Gipson presented a talk, "Impact of A Priori Modeling Errors on the Estimate of UT1 from IVS Intensives", at the 2015 Fall AGU Meeting, on behalf of himself and co-authors Ingrid Strandberg and Armin Azhirnian, both from the Chalmers University of Technology. This talk examined the impact on the estimation of UT1 of errors in the various models used to calculate the theoretical time delay between the reception of quasar signals at two VLBI stations. The talk also discussed the potential use of new estimation strategies as a way of improving the accuracy of UT1 estimation.
2015.12.07: The Journal of Geodesy has accepted a paper by John Gipson and Karen Baver, "Improvement of the IVS-INT01 Sessions by Source Selection: Development and Evaluation of the Maximal Source Strategy". Originally, the IVS-INT01 sessions were scheduled with a small list of quasars that were strong but poorly distributed throughout the sky. The paper evaluates an alternative scheduling strategy, the use of all quasars that are mutually visible at the observing sites in order to improve sky coverage.
2015.12.04: On November 20, 2015, a valued and well-liked member of our group, Rich Strand, passed away. Rich was very knowledgeable about the operation of VLBI stations, and he ultimately became the chief of the Gilmore Creek VLBI station near Fairbanks, Alaska. Most recently, after his retirement from Gilmore Creek, Rich worked part time for NVI, Inc. assisting the Network Coordinator of the International VLBI Service for Geodesy and Astrometry by monitoring station performance and troubleshooting station problems. We are glad to have had the opportunity to know and work with Rich, and we will miss him. Please visit this link for more information about Rich.
2015.09.10: This web site will be unavailable starting on Friday September 11 at approximately 19:00 UTC (15:00 EDT) due to work on the machine that hosts the web site. The work might last a few days. We regret any inconvenience.
2015.08.19: Chopo Ma and David Gordon attended the IAU meeting, held August 3-14 in Honolulu, Hawaii. Ma presented a Division A talk entitled, "Considerations for ICRF3", and Gordon presented a Division A talk entitled, "Revisiting the VLBA Calibrator Surveys for ICRF3". Ma and Gordon also attended the ICRF3 Working Group meeting.
2015.08.10: This web site will be unavailable on Tuesday August 11 from approximately 02:00 to 16:00 UTC (Monday August 10 at 10:00 p.m. to Tuesday August 11 at noon, EDT), due to electrical repairs that will affect our server. We regret any inconvenience.
2015.07.07: Ed Himwich, John Gipson, and Jonathan Quick (HartRAO Observatory) gave a presentation about Field System topics at the June 2015 European VLBI Network 2015 Technical and Operations Group Meeting in Robledo, Spain. Topics included the current Field System release, upcoming releases, caltsys and LO, cable wrap implementation, Field System time and an NTP proposal, Vex2, and many other items.
2015.07.01: On June 30, the day was one second longer than usual. To find out why, click here to check out an article about leap seconds by NASA GSFC's Elizabeth Zubritsky. This article discusses changes in the length of day, VLBI's role in measuring the length of day, planned advances for VLBI, and NASA GSFC's role in VLBI. Two GSFC VLBI group members, Chopo Ma and Dan MacMillan, were interviewed for this article. The article also provides access to an animated video about VLBI, "Greetings from Quasarville, the Town That Never Moves".
2015.06.24: The article, ''The Second Realization of the International Celestial Reference Frame by Very Long Baseline Interferometry'' by Fey et al. was accepted for publication in the Astronomical Journal. This describes work of the ICRF2 Working Group chaired by Chopo Ma (of the GSFC VLBI group), and other authors include David Gordon, Dan MacMillan, Sergei Bolotin, and John Gipson (all from the GSFC VLBI group).
2015.06.15: Members of the GSFC VLBI group presented a total of three talks and four posters at the 22nd Meeting of the European VLBI Group for Geodesy and Astrometry, which was held from May 17 through May 21 in Ponta Delgada, Azores, Portugal. John Gipson presented a talk, "Practical Uses of VGOSDB Format". David Gordon presented a talk on behalf of himself and the VCS-II Team, "Revisiting the VLBA Calibrator Surveys, VCS-II". Dan MacMillan presented a talk, "The CONT Campaigns as a Precursor to VGOS Observing". Karine Le Bail, along with Gordon and Gipson, presented a poster, "Observing Gaia Transfer Sources in R&D and RDV Sessions". Gipson, along with Karen Baver, presented a poster, "Minimization of the UT1 Formal Error through Minimization Algorithms". Sergei Bolotin, along with Baver, Gipson, Gordon, and MacMillan, presented a poster, "Implementation of VGOSDB Format". Finally, Dirk Behrend presented a poster, "Continuous VLBI Scheduling: The CONT14 Example".
2015.05.14: GSFC VLBI group members Dirk Behrend, David Gordon, Ed Himwich, and Rich Strand were teachers at the 8th IVS Technical Operations Workshop (TOW) held May 4-7 at MIT's Haystack Observatory in Westford, Massachusetts. This bi-annual meeting covers all aspects of VLBI data taking. The target audience is VLBI station personnel from around the world.
2015.05.14: John Gipson gave an oral presentation, "A New Model of HF-EOP Derived from 35 Years of VLBI", at the EGU General Assembly 2015. He compared his recent model derived from VLBI data with several other models derived from Space Geodesy (VLBI, GPS, or a combination of the two) as well as models derived from Satellite Altimetry models. Currently the IERS standard model for HF-EOP is given in terms of 12 ortho-tides. Gipson compared models of HF-EOP derived from VLBI which were given in terms of variation at 70 tidal lines vs. models where the variation is given in terms of up to 20 ortho-tides vs. an admittance function approach with up to 100 parameters. Gipson demonstrated that there is significant disagreement between approaches based on estimating variation at the 70 tidal lines vs. either the ortho-tide or the admittance function approaches. Gipson recommends that the various Space Geodesy techniques should use a common empirical model based on tidal variation at 70 tidal lines. This presentation is an update of a talk he gave at the 2014 AGU Fall Meeting.
2015.04.22: This web site will be unavailable from Sunday April 26 17:00 UTC through Monday April 27 05:00 UTC, due to maintenance. This represents a change from the originally scheduled maintenance period. We regret any inconvenience.
2015.04.16: This web site will be unavailable from Sunday April 26 12:00 UTC to Monday April 27 0:00 UTC, due to maintenance. We regret any inconvenience.
2015.01.02: Several members of the GSFC VLBI group contributed to three presentations at the December 2014 Fall AGU. John Gipson gave an invited oral presentation, "Diurnal and Semi-Diurnal Earth Rotation from 35 Years of VLBI Data". Linnea Hesslow, a 2014 GSFC VLBI intern, was a co-author of this presentation. The presentation compared semi-empirical HF-EOP models derived from tidal models and compared them with HF-EOP models estimated using VLBI and/or other Space Geodesy techniques. The tidally derived HF-EOP models agree with each other, and the HF-EOP models estimated using Space Geodesy agree with each other. But there is significant difference between the Tidal models and the Space Geodesy models.

In addition, Dan MacMillan presented "Determination of Galactic Aberration from VLBI Measurements and Its Effect on VLBI Reference Frames and Earth Orientation Parameters". The effect of galactic aberration is not currently included in VLBI analysis, but it is important that it be accounted for in order to maintain a celestial reference frame accurate to the several microarcsecond level. The GSFC VLBI estimate of the component of the aberration vector in the direction of the galactic center (5.3 +/- 0.3 uas/year) is close to estimates made from parallax measurements. The effects of aberration on X and Y nutation estimates are 0.04 uas/year and 0.60 uas/year. The effect on the TRF is less than 0.005 ppb/year for scale and less than 0.01 mm/year for frame translation and rotation.

Finally, three GSFC VLBI staff members (Gipson, Ed Himwich, and Sergei Bolotin) were co-authors of a poster, "The NASA-Haystack VGOS Development Systems", presented by first author Arthur Niell and co-authors Christopher Beaudoin, Roger Cappallo, Brian Corey, Steven McWhirter, Chester Ruszczyk, Jason SooHoo, and Michael Titus (all from MIT Haystack Observatory). This poster discussed the status of the VGOS-capable MIT 18-m antenna in Westford, Massachusetts and the VGOS-capable NASA GGAO 12-m antenna in Greenbelt, Maryland. The discussion included improvements to the digital back ends, the adoption of the Mark 6 recorder, testing of a delay measurement system for the reference frequency cable to the phase calibrator generator, and plans for monthly observations using the two antennas.


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2014

2014.12.03: John Gipson gave an invited presentation, "NASA's Space Geodesy Program---An Informal Perspective", at the 2014 Japan VLBI Consortium Symposium held from October 29 through October 31 in Tsukuba, Japan. This presentation reported preliminary results from the analysis of VLBI broadband data observed by the NASA Space Geodesy Project's prototype core (VLBI, SLR, GNSS, and DORIS) station at GSFC's Goddard Geophysical and Astronomical Observatory. The presentation also discussed NASA's plans to expand the space geodetic network.
2014.11.28: The Journal of Geophysical Research: Solid Earth has accepted a paper by David Eriksson (Cornell University), Dan MacMillan, and John Gipson, "Tropospheric Delay Raytracing Applied in VLBI Analysis". Standard GSFC VLBI operational solutions use elevation-dependent hydrostatic and wet tropospheric mapping functions, which approximate the tropospheric delay at a site as being azimuthally symmetric. Alternatively, the method of raytracing determines a delay along the actual three-dimensional signal path through the troposphere for each VLBI observation. VLBI results were improved when raytrace delays derived from the NASA GSFC GEOS-5 numerical weather model were applied in VLBI analysis.
2014.07.23: John Gipson and Dan MacMillan attended the IERS Unified Analysis Workshop in Pasadena, California on June 27 and 28. Gipson gave a presentation that compared High Frequency Earth Orientation Parameters derived from tidal models and from the VLBI and GPS space geodesy techniques. He also gave a short presentation about differences between the time tags used by different techniques and software packages within space geodesy. MacMillan gave a presentation about effects that contribute to the difference between the scales of the VLBI and SLR terrestrial reference frames.
2014.05.28: The latest official GSFC VLBI ITRF quarterly solution (2014a), quarterly intensive solution (2014a_int) and their associated earth orientation (eop) products can now be accessed through this web site's Data and Results page.
2014.04.11: The GSFC VLBI group participated in the 8th IVS General Meeting, which was held in early March in Shanghai, China. The group gave the following seven oral presentations. Chopo Ma, along with Steven Merkowitz (GSFC) and Briam Luzum (USNO) presented "The Impact of NASA's SGP and USNO on VGOS". Dirk Behrend, Cynthia Thomas, and Ed Himwich presented "CONT14: Preparation and Prospects". Sergei Bolotin, Karen Baver, David Gordon, and Dan MacMillan presented "The VLBI Data Analysis Software nuSolve: Development, Progress, and Plans for the Future". John Gipson presented "IVS Working Group IV and the New Open Format Database". David Eriksson (a former group member now at Chalmers University of Technology), MacMillan, and Gipson presented "Tropospheric Delay Raytracing Applied in VLBI Analysis." Gordon presented "Revisiting the VLBA Calibrator Surveys for ICRF3". Finally, Behrend, Gipson, Ma, and MacMillan helped first author Bill Petrachenko (Natural Resources Canada) and co-authors Hayo Hase (BKG/TIGO), Arthur Niell (MIT Haystack), Axel Nothnagel (Bonn University), and Xiuzhong Zhang (Shanghai Observatory) to present "V2PEG VGOS Observing Plan Proposal".

The GSFC VLBI group also presented the following five posters. Baver and Gipson presented "Balancing Sky Coverage and Source Strength in the Improvement of the IVS-INT01 Sessions". Gipson, Karine Le Bail, and Ma presented "The NASA Goddard Group's Source Monitoring Database and Program". Gordon and Gipson presented "Calc 11 and the Latest Calc/Solve Release". Le Bail, Gordon and Gipson presented "Evaluation of the Stability of ICRF2 Over the Past Five Years Using the Allan Variance". Finally, Thomas, Behrend, and Himwich presented "Transition to Mark 6".

Group members contributed to additional facets of the General Meeting and its auxiliary meetings and activities. Behrend, Gipson, and Himwich served on the General Meeting's Program Committee. Gipson conducted the IVS Analysis Workshop, in his capacity as IVS Analysis Coordinator. In their capacities as IVS Directing Board members, Behrend, Gipson, and Ma participated in the IVS Directing Board meeting. Behrend, Ma, and Thomas participated in the IVS Observing Program Committee meeting. Behrend, Gipson, and Ma participated in the IVS VPEG meeting. Finally, Bolotin gave a demonstration of the nuSolve data analysis software that he has developed.

In addition, Bolotin, Gipson, Gordon, Ma, and MacMillan attended the IAU ICRF-3 working group meeting held in conjunction with the IVS General Meeting.

2014.04.07: The Journal of Geodesy has accepted ''Continental Hydrology Loading Observed by VLBI Measurements'' by David Eriksson (a former intern now at Sweden's Chalmers University of Technology) and Dan MacMillan. This paper discusses the effect on VLBI analysis of applying a hydrology loading series calculated from either the GSFC GLDAS hydrology model or from GRACE mascons. Application of the series reduced baseline length repeatabilities for 80% of the analyzed baselines, site vertical repeatabiliites for 80% of the analyzed sites, and annual site vertical amplitudes for 90% of the analyzed sites.
2014.03.06: The GSFC VLBI Analysis Center has released a new version of Calc/Solve, the 2014.02.21 version. Among other changes, this version implements Calc 11. To find out more about the new version, please access the Calc/Solve release notes. To download the new version itself, please access the Calc/Solve web page and its Getting Calc/Solve section.

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2013

2013.12.30: Dan MacMillan presented "Tropospheric Delay Raytracing Applied in VLBI Analysis" at the Fall AGU in San Francisco, California in mid-December. This poster describes work done by first author David Eriksson (currently at Chalmers University of Technology but formerly of the GSFC VLBI group), and co-authors Dan MacMillan and John Gipson. Standard GSFC VLBI operational solutions use elevation-dependent hydrostatic and wet tropospheric mapping functions that incorrectly assume that tropospheric delay at a site is azimuthally symmetric. The method of raytracing determines a delay along the actual 3-dimensional signal path through the troposphere for each VLBI observation. VLBI results were improved when raytrace delays derived from the NASA GSFC GEOS-5 numerical weather model were applied in VLBI analysis.
2013.12.30: On November 20th the Space Geodesy Group hosted a high level delegation from the Nigerian National Space Research and Development Agency (NASRDA). This delegation included Prof. S. O. Mohammed, the Director-General of NASRDA and several other senior level staff (T. A. Yakubu, Centre for Geodesy and Geodynamics (CGG) Centre Director; Dr. J. Dodo, Head of Space Geodetic Systems, and Prof. Dagogo M. J. Fubara, Consultant to CGG.) The purpose of the visit was to discuss future collaboration between NASA and NASRDA at the CGG site in Toro, Nigeria. In the morning the Nigerian delegation presented their program and gave an overview of their site. This was followed by presentations by several NASA employees and contractors. In the afternoon the Nigerian delegation toured GGAO.
2013.06.06: A VLBA observing proposal entitled 'Second Epoch VLBA Calibrator Survey Observations for ICRF3' was approved by the NRAO for the 13B and 14A semesters (August 1, 2013 - July 31, 2014). David Gordon is the principal investigator, and Chopo Ma is a co-investigator. Other co-investigators are Anthony Beasley (NRAO), David Boboltz (USNO), Patrick Charlot (Laboratoire d'Astrophysique de Bordeaux), Alan Fey (USNO), Ralph Gaume (USNO), Christopher Jacobs (JPL), Alison Peck (NRAO), and Oleg Titov (Geoscience Australia). This proposal grants eight 24-hr sessions to re-observe up to 2,400 single session sources at X/S bands using the new RDBE broadband system. These observations will vastly improve the accuracy of the upcoming ICRF3 (third realization of the International Celestial Reference Frame).
2013.06.06: Dan MacMillan presented "Next Generation VLBI Vector Tie", at the IERS Workshop on Local Surveys and Co-locations held in Paris May 21-22. This presentation discussed VLBI corrections to ground-surveyed reference points of next generation antennas. Due to budgetary constraints on travel, the actual presentation was given by Axel Nothnagel (Bonn University) on MacMillan's behalf.
2013.06.06: Dirk Behrend, Tom Clark, John Gipson, Ed Himwich, and Rich Strand served as primary class and seminar instructors at the 7th Bi-annual Technical Operation Workshop that took place at MIT's Haystack observatory from May 6 to May 9. The workshop was intended to teach VLBI station personnel best practices and to bring them up-to-speed on the latest hardware.
2013.05.08: Ed Himwich gave a presentation via video-conferencing at the EVN TOG (European VLBI Network Technical and Operations Group) meeting in Bonn Germany on April 10. "Field System Topics" discussed the Field System (FS) software package that provides equipment control at VLBI stations. Specific topics included current FS Linux distributions and features of the current and upcoming FS releases. Co-authors were John Gipson and Jonathan Quick (Hartebeesthoek Radio Astronomy Observatory).
2013.04.08: On March 22, eight representatives of the Indian Space Research Organization (ISRO) visited GGAO to tour its VLBI and SLR systems. The representatives expressed some interest in a future VLBI, or other space geodetic, program in India. An Indian VLBI program would provide much needed coverage of a part of Eurasia that is largely unmonitored; the closest antennas are in Russia and China.
2013.03.15: At its 29th meeting, the Directing Board of the International VLBI Service for Geodesy and Astrometry (IVS) accepted a proposal from the SGP that John Gipson be the IVS Analysis Coordinator, one of the permanent IVS positions. The Analysis Coordinator coordinates IVS analysis activities and stimulates VLBI product development.
2013.03.15: The GSFC VLBI group gave five presentations at the 21st Meeting of the European VLBI Group for Geodesy and Astrometry (EVGA) held March 5-8 in Espoo, Finland. John Gipson, Karine Le Bail, and Sergei Bolotin presented "Using a Kalman Filter to Regularize the VLBI Nutation Time Series". This talk described on-going work to develop software to produce a regularly spaced time series from irregularly spaced nutation measurements. Dan MacMillan and former intern David Eriksson presented "Non-tidal Ocean Loading Observed by VLBI Measurements". Non-tidal ocean loading due, for example, to storms can have a significant effect, and this talk demonstrated that including these effects reduces the scatter in VLBI estimates. Bolotin, Karen Baver, Gipson, David Gordon, and MacMillan presented "Current Status of nuSolve", a talk that discussed the capabilities of Goddard's next generation VLBI analysis software and plans for its future development. Le Bail, Gipson, former intern Johanna Juhl, and MacMillan presented "Optimal Time Lags to Use in the Thermal Deformation of VLBI Antennas". VLBI antennas respond to temperature changes by expanding or contracting, with different time lags (delays) for the antenna and its foundation due to their differing materials. In order to determine the optimal time lags for specific antennas and their foundations, this poster evaluated Solve solutions performed with thermal deformation modeling that allowed the authors to vary the time lags. Finally Baver and Gipson presented "Refining the Uniform Sky Strategy for IVS-INT01 Scheduling". In 2009 Gipson had proposed a new strategy for scheduling IVS-INT01 sessions, and this poster investigated ways to update the strategy by using new parameter values in the program that is used to schedule the sessions. Some group members also participated, either in person or via skype, in two splinter meetings, the 14th IVS Analysis Workshop and a joint meeting by the IAU working group on ICRF3 and IAG Sub-Commission 1.4.
2013.03.15: John Gipson and Dan MacMillan were invited to give lectures at the EGU and IVS Training School on VLBI for Geodesy and Astrometry, which was held at Aalto University in Finland from March 2-5. Gipson lectured on how to schedule a VLBI session, and MacMillan lectured on geophysical modeling in VLBI. The school was attended by around 50 young scientists who are studying for a PhD or are at the post-doctoral level. This was the first such school.
2013.02.12: The GSFC VLBI group's 2012-2013 interns, Julia Ringsby and Ronny Videkull, are featured in an article by the Swedish American Chambers of Commerce about three Swedish students at NASA (click here). Ronny and Julia are graduates of Sweden's Chalmers University of Technology, and they are working on developing software to handle the openDB file format.
2013.02.08: John Gipson was on the Thesis Defense Committee for Jing Sun at the Technical University of Vienna, on February 1, 2013. The subject of the thesis was the development of a Very Long Baseline Interferometry (VLBI) scheduling program. The current VLBI scheduling program was developed at NASA over the last 30 years and is currently maintained and developed by Dr. Gipson.
2013.02.08: Starting at 12:30 EST January 29, the 12-m antenna at Goddard Geophysical and Astronomical Observatory (GGAO) participated in International VLBI Service (IVS) session RD1301. This is the first 24-hour observing session in which a NASA-developed broadband VLBI (Very Long Baseline Interferometry) station participated with a network of IVS stations that use standard S/X-band systems. The 12-m antenna and broadband electronics at GGAO functioned properly.
2013.01.10: Members of the GSFC VLBI group gave three presentations at the Fall AGU in December 2012. Dan MacMillan gave a talk about his work with former group member David Eriksson on surface mass loading. "Explaining the VLBI Estimated Degree-1 Load Variation Via Atmospheric, Oceanic, and Hydrological Mass Variations" discussed improvements in VLBI analysis from the modeling of these components of loading. In addition, the degree-1 deformation due to loading mass was estimated from the VLBI data, yielding estimates of annual geocenter variation. John Gipson presented a poster about his work with first author Karine Le Bail, Dan MacMillan and former group member Johanna Juhl about bad met data in VLBI processing. "Improving the Homogeneity of Meteorological Data to Minimize Resulting Errors in Geodetic Analysis" discussed the impact of bad met data on VLBI processing and the use of pressure and temperature series derived from the ECMWF Era-Interim model to improve VLBI solutions. Finally, on behalf of the first author, Chopo Ma presented "Next Generation NASA Initiative for Space Geodesy" (Stephen Merkowitz et al.), which discussed the status of NASA's efforts to establish a prototype space geodetic station that has integrated next generation SLR, VLBI, GNSS, and DORIS systems and a system for providing accurate vector ties between them.

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2012

2012.11.16: Chopo Ma, Larry Hilliard, Ed Himwich, Dirk Behrend, and Tom Clark attended the 1st International VLBI Technology Workshop held at the MIT Haystack Observatory from October 22-24. This workshop focused on VLBI digital systems (e.g., digital backends, data buffering and recording systems, correlators, and e-VLBI technology) and their integrated use for VLBI applications. The group members attended presentations and participated in splinter meetings, including meetings to discuss remote control of antennas, antenna Monitor and Control Infrastructure, Digital Base Band Converter radiometry, and observing with the new Deep Space Network VLBI Processor.
2012.11.16: "Quantifying the Correlation between the MEI and LOD Variations by Decomposing LOD with Singular Spectrum Analysis", by Karine Le Bail, John Gipson, and Daniel MacMillan, has been accepted for publication in IAG Symposia 39. This paper discusses the authors' use of singular spectrum analysis to extract various components from a Length of Day (LOD) time series in order to quantify the correlation between the El Niño-Southern Oscillation (ENSO) signal and the Length of Day.
2012.08.27: Chopo Ma gave a presentation at the Solar System Exploration Seminar for the Director of Science and Exploration held August 22 at NASA GSFC. The international VLBI community is currently implementing the next generation VLBI system, VLBI2010, which will use improved technology to meet new requirements, such as a need to observe phenomena with magnitudes of a few millimeters like sea level rise. Ma's presentation, "The Development of the VLBI2010 Global Observing System (VGOS)", discussed the status of the deployment of a global network of VLBI2010 antennas and NASA's work on the VLBI2010 electronics. Topics in this presentation included the goals for VGOS (e.g., 1 mm precision from 24 hrs of observing), the NASA antenna design, progress in VLBI2010 front and back ends at GSFC's GGAO station, and results from two short test sessions that were observed this year. Delays were computed using all cross-correlations from two polarizations in each of four, well-spaced RF bands along with simultaneous ionosphere estimation. Dirk Behrend was this presentation's co-author.
2012.07.26: The latest official GSFC VLBI ITRF quarterly solution (2012a, July 2012), quarterly intensive solution (2012a_int) and their associated earth orientation (eop) products can now be accessed through this web site's Data and Results page.
2012.07.06: On June 30, the day was one second longer than usual. To find out why, click here to check out an article about leap seconds by NASA GSFC's Elizabeth Zubritsky. This article explains changes in the length of day, VLBI's role in measuring the length of day, and NASA GSFC's role in VLBI. A GSFC VLBI analyst, Dan MacMillan, contributed information to this article, and the article also shows the VLBI antenna at Kokee Park, Hawaii that is jointly managed by NASA and the United States Naval Observatory.
2012.07.06: Ed Himwich made two presentations at the EVN TOG (European VLBI Network Technical and Operations Group) meeting held on June 27 and 28 in Onsala, Sweden. Both presentations discussed the Field System (FS) software package that provides equipment control at VLBI stations. "FS DBBC Support" discussed issues in the Field System's support of DBBCs (Digital Base Band Converters), which convert incoming analog radio signals to a digitized, lower frequency. "FS Topics", which Himwich gave on behalf of himself and co-authors John Gipson and Jonathan Quick (Hartebeesthoek Radio Astronomy Observatory), discussed near-term plans for general Field System development.
2012.06.01: The latest GSFC VLBI quarterly nuvel solution (2011an) is now available on the 2011an web page.
2012.05.30: Three new services (hydrology loading, non-tidal ocean loading, and temperature and pressure) are now available through this web site. For details, please visit our data and results page's "other links" section.
2012.04.13: John Gipson gave a presentation about VLBI2010 at the Main Astronomical Observatory (Kiev, Ukraine) on March 13. The presentation gave a general overview of the VLBI2010 system and described NASA's role in the development of this system.
2012.04.13: 13 members of the GSFC VLBI group contributed to 17 talks, posters, and reports at the March 2012 General Meeting of the International VLBI Service for Geodesy and Astrometry (IVS). Group members were first authors of 13 of the 17 presentations. The group presented work in all five sessions of the meeting, and the work covered a variety of topics including IVS plans and activities, scheduling, technology, analysis techniques, analysis results, data formats, software, and the March 2011 Tohoku earthquake.
2012.02.09: The latest official GSFC VLBI ITRF quarterly solution (2011b, December 2011), quarterly intensive solution (2011b_int) and their associated earth orientation (eop) products can now be accessed through this web site's Data and Results page.
2012.01.11: Dan MacMillan, Dirk Behrend, and Shinobu Kurihara (Geospatial Information Authority of Japan) presented "Effects of the 2011 Tohoku Earthquake on VLBI Geodetic Measurements" at the 2011 AGU Fall Meeting. The March 2011 earthquake near Honshu, Japan had a significant impact on the IVS Intensive (rapid UT1) observing program because of the epicenter's proximity to the Tsukuba station, which is a key station in two Intensive series. The use of a station in UT1 estimation requires that the station's position be well-known, but the earthquake moved Tsukuba, and its motion is still continuing, requiring IVS to continually re-establish Tsukuba's position. The poster discussed efforts to establish Tsukuba's position variation after the earthquake well-enough that it can be used again for operational UT1 estimation. The poster also compared UT1-UTC results using Tsukuba's post-quake positions to results from an Intensive series that does not involve Tsukuba and was not affected by the earthquake.
2012.01.11: David Eriksson and Dan MacMillan presented "Continental Hydrology Loading Observed by VLBI Measurements" at the 2011 AGU Fall Meeting. This poster discussed the site position deformation due to hydrological loading at VLBI stations and the reduction in baseline length and site position scatter achieved by the application of hydrology loading series computed from the GLDAS hydrology model and a loading series derived from GRACE mascons.

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2011

2011.12.16: Chopo Ma chaired the December 3, 2011 meeting of the IERS Directing Board, and he also presented the IVS' report to the IERS. The report was assembled by Dirk Behrend, the IVS Coordinating Center Director, and it discussed IVS operations (the status of network stations and the Intensive observing program), IVS analysis (combination solutions and software development and comparisons), the status of VLBI2010 development, and results from the CONT11 observing campaign.
2011.12.07: On November 28, David Eriksson presented "Mass Loading in VLBI Analysis" to the VLBI group at GSFC. This presentation expanded upon two earlier presentations about topographic pressure loading and hydrology loading that Dan MacMillan and Eriksson had given at the September GGOS Unified Analysis Workshop. The new presentation discussed the use of a new model in Eriksson and MacMillan's pressure loading analysis, and the presentation also discussed the addition of new data, the application of new statistical tests, and the improvement of precision in the authors' hydrology loading analysis.
2011.12.07: On November 13, Dirk Behrend gave an invited presentation, "The Antarctic VLBI Station O'Higgins as a Network Station of the IVS", at the '20 Years Antarctic Research Station GARS O'Higgins' symposium in Punta Arenas, Chile. His co-authors were Harald Schuh (TU Vienna), Chopo Ma, Ed Himwich, and Cynthia Thomas (all GSFC). The talk covered the history of the VLBI station O'Higgins in the IVS observing program and presented selected results based on the station's participation. The presentation also gave a brief outlook on a possible future extended usage of O'Higgins in geodetic VLBI.
2011.11.17: In October, Johanna Juhl presented "The Effect and Use of Meteorological Data in VLBI Processing at GSFC" to the VLBI group at GSFC. This presentation expanded upon an earlier presentation by Karine Le Bail, Juhl, and John Gipson at the September GGOS Unified Analysis Workshop. The new presentation included work by Dan MacMillan and David Eriksson, and it gave more information about the procedures used in the analysis of the met data and the results of the analysis.
2011.10.25: Dan MacMillan gave three presentations about recent GSFC VLBI group research at the September 16-17 GGOS Unified Analysis Workshop. The first presentation was "Hydrology Loading in VLBI Analysis", which discussed work done by David Eriksson and Dan MacMillan to investigate the use of hydrology loading series from GSFC GRACE mascons and from GSFC GLDAS data in VLBI analysis. The second presentation, "Pressure Loading Issues in VLBI Analysis," summarized work done by MacMillan and Eriksson on the effect of topography on atmospheric loading, the bias between two reference pressure fields, and comparisons of observation level and 24-hour average pressure loading corrections. The last presentation, by Karine Le Bail, Johanna Juhl, and John Gipson, was entitled "Meteorological Data in VLBI Processing at GSFC: Importance and Strategy to Improve the Databases used by Calc/Solve". This presentation discussed deficiencies in the met data in VLBI databases (for example, missing data and incorrect data), and it assessed the impact of these deficiencies on VLBI analysis. The talk then discussed strategies (for example, using ECMWF data) to obtain a complete, homogeneous set of met data.
2011.10.13: Chopo Ma presented "NASA's Next Generation Space Geodesy Project at GGAO" at the GGOS Unified Analysis Workshop held September 16-17. A primary goal of GGOS is to integrate geodetic techniques, and NASA is building a prototype of a next generation space geodetic station intended to integrate the techniques of VLBI, SLR, GNSS, and DORIS. Ma's presentation described the prototype and reported on its status, including the installation and testing of its VLBI2010 antenna and the testing of technologies to tie the co-located techniques together.
2011.10.13: Dirk Behrend attended the First ICSU World Data System conference "Global Data for Global Science" held in Kyoto, Japan from September 3-6, 2011. He gave a poster presentation about the "Activities of the International VLBI Service". The poster introduced the VLBI technique and its scientific role, described the IVS and its products, components, and data centers, and gave a short introduction to VLBI2010. The IVS has been accepted as a member of the WDS pending signing a commitment agreement.
2011.07.27: On July 7, Chopo Ma gave an invited presentation, "Establishing Celestial Reference Frames at Different Ranges of Wavelengths", at the JENAM-2011 European Week of Astronomy and Space Science of the European Astronomical Society in St. Petersburg, Russia. His co-authors were A. Andrei (Observatorio Nacional/MCT), G. Bourda (Laboratoire d'Astrophysique de Bordeaux), and C. Jacobs (JPL). The talk covered the ICRF2 (International Celestial Reference Frame 2), catalogs at higher radio frequencies, the selection of transfer objects in preparation for Gaia, and the Gaia quasar catalog.
2011.07.22: During August 2008, the IVS observed CONT08, a two-week campaign of continuous VLBI sessions. The Journal of Geodesy has devoted a special issue to CONT08, and two members of the GSFC VLBI IVS Analysis Center (GSFC AC), Sergei Bolotin and Dan MacMillan, are co-authors of one of this issue's articles. "VLBI-derived troposphere parameters during CONT08" by Robert Heinkelmann (DGFI AC), Johannes Böhm (IGG AC), Sergei Bolotin (GSFC AC), Gerald Engelhardt (BKG/IGGB AC), Rüdiger Haas (OSO AC), Roberto Lanotte (CGS AC), Dan MacMillan (GSFC AC), Monia Negusini (INAF AC), Elena Skurikhina (IAA AC), Oleg Titov (GA AC), and Harald Schuh (IGG AC), is in the Journal of Geodesy, Springer, Vol. 85, No. 7, pp. 377–393, DOI: 10.1007/s00190-011-0459-x, http://dx.doi.org/10.1007/s00190-011-0459-x .
2011.07.22: The GSFC VLBI group presented two talks and a poster at the IUGG XXV General Assembly held June 27 through July 8 in Melbourne, Australia. Karine Le Bail presented "The Construction of the ICRF2 and its impact on the Terrestrial Reference Frame", by Karine Le Bail, Chopo Ma, David Gordon, Dan MacMillan, Sergei Bolotin, and John Gipson. This talk discussed the formation, the composition, and some characteristics of the current fundamental celestial reference frame (ICRF2), the impact on the Terrestrial Reference Frame of switching from the previous fundamental celestial reference frame (ICRF), and the criteria used for choosing sources from the ICRF2 for regular use in geodetic VLBI. Karine Le Bail also presented "Decomposing LOD with Singular Spectral Analysis", by Karine Le Bail, Dan MacMillan, and John Gipson. This talk discussed the authors' use of singular spectral analysis to extract various components from a Length of Day (LOD) time series in order to search for the correlation of the El Niño-Southern Oscillation (ENSO) signal in the form of the Multivariate ENSO Index (MEI). Finally, Dirk Behrend, Karine Le Bail, Chopo Ma, Jan McGarry (GSFC SLR group), and John Gipson presented a poster, "Activities towards an Integrated Site of Next Generation Geodetic Instruments at GGAO", which presented minor updates to an earlier poster that discussed progress towards the next generation VLBI and SLR systems at GSFC's GGAO station.
2011.06.06: The latest official GSFC VLBI ITRF quarterly solution (2011a, April 2011), quarterly intensive solution (2011a_int) and their associated earth orientation (eop) products can now be accessed through this web site's Data and Results page.
2011.06.03: Three members of the GSFC VLBI group supported the Sixth IVS Technical Operations Workshop (TOW2011) held May 9-12 at the MIT Haystack Observatory. Dirk Behrend and Ed Himwich worked with Haystack personnel to organize the TOW, and Himwich and David Gordon presented a total of seven classes and sessions. Gordon presented "Reference Frames, EOP, and Modeling VLBI Delays", which explained the celestial reference frame, the terrestrial reference frame, EOP, and their relationship, as well as how the CALC program computes theoretical delays. In conjunction with Brian Corey (MIT Haystack), Himwich taught "General Station Troubleshooting", which described tests that stations should perform to evaluate their performance. Himwich taught three additional classes, "Automated Pointing Models Using the FS" (how to take and analyze pointing measurements), "Writing Station Specific FS Code" (how to interface station-specific code with the VLBI Field System), and "Impact of Operations on Data Analysis" (the effect of data acquisition problems such as clock breaks on data analysis). Himwich also gave a presentation, "Field System Near Term Future Plans", about plans for Field System development, including collaborations among various groups. Finally, Himwich led "Topics in FS Station Software Coding", a group discussion and demonstration that allowed participants to ask advice about implementing specific features in the Field System.
2011.05.06: Chopo Ma gave an invited talk at the Wegener session of the EGU 2011 General Assembly held in April in Vienna, Austria. "The IVS and Its Impact on Geodesy and Geophysics" discussed the International VLBI Service for Geodesy and Astrometry and its products and services (e.g., ICRF2 and its monitoring of Earth orientation). The talk included some of the science behind VLBI (the geophysical effects on Earth orientation) and some specific results (a 24 year series of Earth orientation estimates). Finally, the talk discussed the need to upgrade the VLBI technique and equipment to meet challenges such as 1-mm accuracy in the estimation of station coordinates, and it discussed the IVS’ response--- the new generation of VLBI, VLBI2010---including general characteristics of a VLBI2010 system.
2011.05.06: Members of the GSFC VLBI group presented three posters at the EGU 2011 General Assembly. Dan MacMillan and Dirk Behrend presented "VLBI2010: Next Generation VLBI System for Geodesy and Astrometry", along with Bill Petrachenko (Natural Resources Canada), Arthur Niell and Brian Corey (MIT Haystack Observatory), Harald Schuh (Vienna University of Technology), and the 17 member Broadband Development Team. The poster described VLBI2010, compared it to the current VLBI system, and reported on the progress of NASA’s VLBI2010 development. Dirk Behrend, John Gipson, Chopo Ma, and Jan McGarry (GSFC SLR) presented "GGAO as an Integrated Geodetic Site". This poster discussed progress towards the next generation VLBI and SLR systems at GSFC’s GGAO station, which is one of only two stations with four co-located space geodetic techniques, making it important as a test bed for co-locating techniques. Finally John Gipson and Karen Baver, along with Kerry Kingham and Merri Sue Carter (both of USNO) presented "Better Scheduling of the IVS-Intensives for Improved UT1 Estimates". This poster presented results from the analysis of a series of R&D sessions that tested a new strategy for scheduling IVS’ INT01 sessions, as well as results from the analysis of the first operational sessions that were scheduled with the new strategy.
2011.05.06: On April 11, 2011, John Gipson gave a talk at the Vienna Technical University about improving VLBI estimates through the inclusion of station dependent noise and correlated noise. The talk gave evidence for station dependent noise and correlation between observations, presented methods for correcting the noise and correlation, and discussed the effect of implementing these corrections on statistical measures such as baseline scatter and repeatability.
2011.04.08: Several members of the GSFC VLBI group attended or supported the 20th EVGA Meeting held March 29-30 at the Max-Planck-Institut für Radioastronomie, in Bonn, Germany. Group members gave several presentations, including "Assessing the Accuracy of Geodetic Measurements for the VLBI2010 Observing Network" (Dan MacMillan), "Strategy to Improve the Homogeneity of Meteorological Data in CALC/SOLVE Databases" (Karine Le Bail and John Gipson), and "Current Status of Development of New VLBI Data Analysis Software" (Sergei Bolotin, John Gipson, David Gordon, and Dan MacMillan). In addition Dirk Behrend chaired session 7 of the meeting.
2011.03.11: Several members of the GSFC VLBI group attended the 2011 East Coast Geodetic VLBI Workshop held at the MIT Haystack Observatory on February 23 and 24. The attendees discussed several observing, correlation, analysis, and VLBI2010 issues. In addition, GSFC VLBI group members gave presentations, including a presentation about the importance of met data for VLBI processing (Karine Le Bail), the results of a VLBI2010 survey of the IVS Network Stations conducted by the IVS VLBI2010 Project Executive Group (Dirk Behrend), and a demonstration of an analysis software package being developed within the group (Sergei Bolotin).
2011.02.09: On January 27, Chopo Ma gave an invited presentation, "The ICRF, ITRF, and VLBA", at a workshop about the future of the Very Long Baseline Array at NRAO headquarters. The presentation discussed the International Celestial and Terrestrial Reference Frames and the importance of the VLBA for supplying data for them.
2011.01.06: Karine Le Bail gave an oral presentation at the 2010 Fall AGU on "Using the Singular Spectral Analysis Method to Analyze VLBI Time Series". Le Bail and co-authors Erik Nilsson (Chalmers University of Technology) and John Gipson analyzed with the Singular Spectral Analysis method a UT1-UTC time series (1979-2010) obtained with VLBI. This permitted them to decompose the time series into a tendency and periodic signals of different amplitudes (annual, semi-annual, 14-year and 2.4-year). The Allan variance was used to detect white noise.
2011.01.06: Chopo Ma presented a poster at the 2010 Fall AGU on "VLBI 2010’s Role in an Integrated Geodetic Site". This presented the rationale for a network of Integrated Geodetic Stations, described the layout of such a station, and gave recommendations for the size of such a network.
2011.01.06: Dan MacMillan, Arthur Niell (MIT Haystack Observatory), and John Gipson presented a poster at the 2010 Fall AGU. "Assessing the Accuracy of Geodetic Measurements from the VLBI2010 Observing Network" investigated the effect of several systematic errors on the accuracy of VLBI2010 measurements. Biases in site position at the 1-2 mm level can arise from troposphere mapping function error, gravitational antenna deformation, or site pressure errors. Errors caused by troposphere turbulence have latitude dependence that leads to vertical precision errors of 1-3 mm, but no significant biases.
2011.01.06: Sergei Bolotin, John Gipson, David Gordon, Karine Le Bail, and Dan MacMillan presented a poster at the 2010 Fall AGU. "Validation of Tropospheric Parameters Estimating from VLBI Data Analysis" reported that a comparison of wet zenith delay estimates obtained with two independent packages of VLBI data analysis software, water vapor radiometer measurements, and GPS-derived results showed good agreement, with WRMS residuals of mutual differences on the level of 5-10 mm.
2011.01.06: John Gipson, Karine Le Bail, Sergei Bolotin, David Gordon, and Dan MacMillan presented a poster at the 2010 Fall AGU on the "Impact of Erroneous Meteorological Data on VLBI Processing". Bad or missing pressure data at a station results in errors in the estimation of local Up. The poster explored the feasibility of using ECMF data to replace missing pressure data. This approach works, but care must be taken to make sure there is no offset between the pressure data from local met sensors.
2011.01.06: Dirk Behrend, Dan MacMillan, and several co-authors presented a poster, "VLBI Observations of the 2010 Chilean Earthquake". The poster described the available VLBI data prior to and after the earthquake. Five dedicated sessions were added to the regular IVS observing program in order to densify the data points in the VLBI time series. The VLBI data indicate that the Up and North components of the position time series can be modeled as a co-seismic offset. The East component, however, needs to be modeled using, for instance, a transient decay model for the post-seismic effect. Additional co-authors are John Gipson, Hayo Hase (BKG TIGO Observatory), Jim Lovell (University of Tasmania), Mike Poirier (MIT Haystack Observatory), and Ronald Curtis and Mark Evangelista (both from Honeywell Technology Solutions, Inc.).

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2010

2010.12.28: The latest official GSFC VLBI ITRF quarterly solution (2010a, June 2010), quarterly intensive solution (2010a_int) and their associated earth orientation (eop) products can now be accessed through this web site's Data and Results page.
2010.12.11 Chopo Ma accompanied John LaBrecque, NASA program manager for Solid Earth and Interior, on a visit to the Norwegian Mapping Authority (NMA) and the Norwegian Ministry of the Environment to support the NMA's proposal for an integrated space geodesy station at its Ny-Ålesund site. Ma also discussed with NMA staff their plans for VLBI analysis using the GEOSAT software developed at the Norwegian Defense Research Establishment.
2010.11.09 John Gipson gave an invited talk on ``High Frequency Tidal EOP from Space Geodesy and Ocean Modeling’’ at the October 2010 GGOS/IAU Workshop held in Shanghai, China. Gipson and co-author Richard Ray (GSFC) compared high frequency (i.e., diurnal and semi-diurnal) variations in EOP derived from VLBI and GPS with predictions derived from two tidal models of the oceans based on Topex/Poseidon data. The presentation built upon a presentation that Gipson and Ray gave on this topic at the June 30, 2010 IGS Workshop. (See the 2010.07.28 news release.)
2010.10.15 The Journal of Geodesy recently accepted "Monte Carlo Simulations of the Impact of Troposphere, Clock, and Measurement Errors on the Repeatability of VLBI Positions" by Andrea Pany, Johannes Böhm, Dan MacMillan (GSFC), Harald Schuh, Tobias Nilsson, and Jörg Wresnik. The paper discusses simulations carried out by the IGG/University of Technology, Vienna and the Goddard VLBI group to design the next generation VLBI2010 system. Some of the results from the paper are that 1) the troposphere delay modeled here with a turbulence model is the dominant error source, 2) the simulated 3D RMS site precision for the CONT05 experiments is close to the observed precision, 3) the 3D RMS site position precision is not improved significantly with clocks more accurate than current operational masers, and 4) the 3D RMS site position error increases roughly linearly with the tropospheric structure constant, which can depend on latitude, station height, and tropospheric water vapor variability.
2010.10.15 Chopo Ma made two presentations at the IAG Reference Frames for Applications in Geosciences Symposium. The first talk was "Effects of ICRF2 on the TRF, CRF and EOPs" by David Gordon, Chopo Ma, Dan MacMillan, Sergei Bolotin, Karine Le Bail, and John Gipson. It discussed the effects of using the second International Celestial Reference Frame on the terrestrial and celestial reference frames and on the estimation of earth orientation parameters. The second presentation, entitled "Comparison of Realizations of the Terrestrial Reference Frame" by Ma, MacMillan, Bolotin, Le Bail, Gipson, and Gordon, compared the IGN and DGFI realizations of ITRF2008. This presentation also discussed the effect on EOP estimates when the TRF was fixed to the IGN or DGFI TRF in VLBI solutions. In addition, Le Bail was a co-author of "IDS Evaluation of ITRF2008", by Frank Lemoine et al.
2010.10.15 The Main Astronomical Observatory (MAO) of the National Academy of Sciences of Ukraine has published the proceedings of the 6th Orlov Conference, including four papers to which two GSFC VLBI group members contributed. Dirk Behrend was a co-author of "The IVS on its Way to the Next Generation VLBI System", which discusses some of the IVS’ goals for the next generation VLBI system (VLBI2010) and the next steps for achieving these goals. The other authors are first author Harald Schuh (IGG), Bill Petrachenko (Geodetic Survey Division, NRCan), Arthur Niell and Brian Corey (MIT Haystack), and Jörg Wresnik (IGG). The second GSFC VLBI group member, Sergei Bolotin, was a co-author of the other three papers: "Individual and Combined Solutions of Celestial Reference Frame" (Bolotin et al.), "Investigation of the EOP Data Sets" (Bolotina et al.), and "High Frequency Nutation from GRGS Multi-technique Combination" (Bizouard et al.). These papers present work Bolotin did while at the MAO.
pointer to July 28, 2010 news item
2010.07.28 On June 30, 2010, John Gipson gave an invited talk on ``High Frequency Tidal EOP from Space Geodesy and Ocean Modeling’’ at the 2010 IGS Workshop in Newcastle upon Tyne, England. In this talk Dr. Gipson compared high frequency (i.e., diurnal and semi-diurnal) variations in EOP derived from VLBI and GPS with predictions derived from two tidal models of the oceans based on Topex/Poseidon data. His main conclusions were that: 1) The empirical results agree well with each other, as do the two tidal models. 2) There are significant differences between the space geodesy estimates and the tidal model predictions. 3) Including libration reduces, but does not eliminate, the difference between the tidal models and the space geodesy estimates. Much of the remaining difference is due to the `ortho-tide’ assumption used in the tidal models.
2010.07.02 Ed Himwich gave a presentation about the Field System, the system that operates VLBI antennas, at the European VLBI Network Technical and Operations Group (EVN TOG) meeting held at the Metsähovi Radio Observatory (MRO) in Helsinki, Finland on June 21-22. "Field System Topics" reviewed the current status of the Field System and reported plans for its future development.
2010.07.02 Chopo Ma gave a presentation at a meeting that was held on June 1 at the Canadian Geodetic Survey for the purpose of promoting North American GGOS collaboration. A primary goal of GGOS is to integrate geodetic techniques, and NASA is building a prototype of a space geodetic observatory intended to integrate the techniques of VLBI, GNSS, SLR, and DORIS. Ma’s presentation, "NASA’s Prototype Integrated Observatory" described the SGP (Space Geodesy Program) prototype and reported on its status.
2010.06.11 The GSFC VLBI analysis center recently released its latest Calc/Solve software version, the 2010.05.21 release. Major improvements include the generation of nutation in the X/Y coordinate system and the generation of Vienna Mapping Function (VMF) troposphere files. For a description of all improvements and bug fixes, as well as important information, including Calc/Solve files that must be updated in order to use the new version, please go to the 2010.05.21 release notes. To obtain the new version itself,i please contact the GSFC VLBI group.
2010.06.11 Chopo Ma (GSFC), Arthur Niell (Haystack Observatory), Harald Schuh (TU Vienna) and Dave Boboltz (USNO) were invited to the National Astronomy and Ionosphere Center Arecibo Observatory for a workshop on "Science with the New Arecibo 12-m" Ma gave a review presentation on the celestial reference frame. Ma and Niell also visited the 12-meter antenna being assembled on a hill near the observatory entrance.
2010.04.06 Previously, the Astronomical Journal accepted a paper that presents the results of a collaboration between members of GSFC, JPL, NRAO, USNO and the Bordeaux Observatory. "The Celestial Reference Frame at 24 and 43 GHz. I. Astrometry" by G. E. Lanyi et al. presents and discusses the celestial reference frames at K and Q bands. The Astronomical Journal has now published this paper online, and it is available here. (Please note that this paper should be cited as "The Astronomical Journal 139 (2010) 1695-1712".) Two members of the GSFC VLBI group, Chopo Ma and David Gordon, are members of the collaboration group and are co-authors of this paper.
2010.04.05 Earlier this year, the Astronomical Journal accepted a paper that presents the results of a collaboration between members of GSFC, JPL, NRAO, USNO and the Bordeaux Observatory. "The Celestial Reference Frame at 24 and 43 GHz. II. Imaging" by P. Charlot et al. presents images and structure information for several hundred sources at K and Q bands. The Astronomical Journal has now published this paper online, and it is available here. (Please note that this paper should be cited as "The Astronomical Journal 139 (2010) 1713-1770".) Two members of the GSFC VLBI group, Chopo Ma and David Gordon, are members of the collaboration group and are co-authors of this paper.
2010.03.29: The latest official GSFC VLBI ITRF quarterly solution (2009a, November 2009), quarterly intensive solution (Int24) and their associated earth orientation (eop) products can now be accessed through this web site's Data and Results page.
2010.03.08 The Astronomical Journal has accepted two papers that present the results of a collaboration group that was formed between members of GSFC, JPL, NRAO, USNO and the Bordeaux Observatory to extend the celestial reference frame to higher frequencies (K and Q bands at ~24 and ~43 GHz, respectively). "The Celestial Reference Frame at 24 and 43 GHz. I. Astrometry" by G.E. Lanyi et al. presents and discusses the celestial reference frames at K and Q bands. A companion paper, "The Celestial Reference Frame at 24 and 43 GHz. II. Imaging" by P. Charlot et al., presents images and structure information for several hundred sources at K and Q bands. Two members of the GSFC VLBI group, Chopo Ma and David Gordon, are members of the collaboration group and are co-authors of both papers.
2010.03.08 In conjunction with the IVS 2010 General Meeting, which was held in Hobart, Tasmania, Australia, some members of the GSFC VLBI group visited the new 12 meter VLBI2010 antenna at Hobart and attended its formal dedication. Group members also visited the Auckland University of Technology's new 12 meter VLBI2010 antenna at Warkworth, New Zealand.
2010.03.02 The 10 members of the GSFC VLBI group contributed to a total of 20 talks, posters, and reports at the February 2010 General Meeting of the International VLBI Service for Geodesy and Astrometry (IVS). Group members were first authors of 14 of the 20 presentations, and one of the remaining six presentations described work done by the first author while he was a member of the GSFC VLBI group in 2009. The group presented work in all five sessions of the meeting, and the work covered a variety of topics including IVS plans and activities, scheduling, technology, analysis techniques, analysis results, data formats, and new software. Due to space limitations, only the following, partial sample of the presentations will be mentioned here, with an emphasis on newer work.

``Coordinating, Scheduling, Processing and Analyzing IYA2009'' by John Gipson, Dirk Behrend, David Gordon, Ed Himwich, Dan MacMillan, Mike Titus (MIT Haystack), and Brian Corey (also MIT Haystack) described the life cycle and challenges of the largest geodetic experiment in the history of VLBI, which was observed in November 2009 as part of the International Year of Astronomy. ``Strategies for Improving the IVS-INT01 UT1 Estimates: Results of RD0907 through RD0910'' by Karen Baver, John Gipson and Dan MacMillan gave a preliminary evaluation of a new strategy proposed by Gipson for scheduling the IVS-INT01 Intensive sessions. ``RDV77 VLBA Hardware/Software Correlator Comparison'' by David Gordon compared the performance of the VLBA's new software correlator to its current hardware correlator based on their processing of the RDV77 session. ``Use of GPS TEC Ionosphere Maps for Calibrating Single Band VLBI Sessions'', also by David Gordon, presents the K/Q Collaboration Group’s evaluation of the usefulness of GPS total electron content maps for reducing biases in source positions from data collected at various bandwidths. ``Time-dependent Selection of an Optimal Set of Sources to Define a Stable Celestial Reference Frame'' by Karine Le Bail and David Gordon updates previous source time series studies done by Martine Feissel-Vernier (Paris Observatory) and proposes an alternate method of analyzing source time series. ``Development of a New VLBI Data Analysis Software'' by Sergei Bolotin, John Gipson and Dan MacMillan introduced a new analysis software system being developed by Bolotin to implement new models and data analysis techniques. Finally, ``The Composition of the Master Schedule'' by Cynthia Thomas, Dan MacMillan, and Dirk Behrend explained the way in which Thomas and Behrend determine the IVS sessions and observing networks each year as part of their work for the IVS Coordinating Center.
2010.01.09 Dan MacMillan gave a poster presentation entitled “VLBI-SLR Combination Solution using GEODYN” with co-authors Despina Pavlis, Frank Lemoine, Doug Chinn, and Dave Rowlands at the Fall 2009 AGU meeting. The goal of this work is to combine all of the geodetic techniques at the observation level. The poster gave the results of comparisons between Calc/Solve and GEODYN VLBI solutions, as well as the results of a VLBI+SLR combination solution.
2010.01.09 Chopo Ma and Dan MacMillan attended the Second GGOS Unified Analysis Workshop held on December 11-12, 2009 before the AGU meeting. A primary goal of GGOS is to combine and integrate the different geodetic techniques, and the purpose of the workshop was to address 1) products of the geodetic services, 2) modeling deficiencies, 3) combination strategies, and 4) network simulations and analyses. Ma reported on the present and future status of IERS products.
2010.01.09 Chopo Ma gave two presentations at the December 16, 2009 meeting of the GGOS Bureau on Networks and Communications (BNC). One presentation was a condensed report on work done by a recent GSFC VLBI group member, Benno Schmeing, on the automation of VLBI antenna surveying. The second presentation was a report on the activities of the International VLBI Service for Geodesy and Astrometry (IVS) since the initial BNC meeting in April 2009.

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2009

2009.11.16: As an activity for the International Year of Astronomy 2009 (IYA2009), the IVS is organizing a special astrometric session, IYA09, in which an unprecedented number of VLBI stations will participate. For 24 hours starting at November 18, UT 18:00, 35 stations will observe as many of the 295 sources in the newly adopted ICRF2 reference frame as possible. This will provide an initial baseline for monitoring the ICRF2. The session goes hand in hand with outreach activities at the stations and other places, and a press statement was released through the IYA2009. Members of the GSFC VLBI group have significantly contributed to the organization of this session; this includes general coordination, schedule creation, and media planning. The GSFC VLBI group will also play a major role in the analysis of the session. More information is available at http://ivscc.gsfc.nasa.gov/program/iya09.
2009.11.16: In October, Karine Le Bail gave a talk "Selection of an Optimal Set of Sources to Define a Stable CRF" to the VLBI group at GSFC. This work is an update of previous studies from Martine Feissel-Vernier (A&A, 2003) applied to ICRF2 sources (GSFC time series solution from David Gordon). In addition, it proposes an alternate method of analyzing VLBI source time series and evaluating the statistical time stability of VLBI sources using the Allan variance. Le Bail compared her selection of stable sources to the selection of Martine Feissel-Vernier (2003) and to the ICRF2 defining sources. The 295 defining sources show good stability, and the selection of Le Bail, which ranges from 106 to 128 sources depending on whether noise is taken into account, indicates a stable core of VLBI sources.
2009.11.09: A recent GSFC popular science news article, "New Celestial Map Gives Directions for GPS", explains the role of the ICRF (International Celestial Reference Frame) in establishing the positions of GPS satellites, as well as its role in assisting spacecraft navigation and mapping celestial objects. The article in turn describes the contribution of the VLBI technique to the generation of the ICRF. The efforts of the IAU and the IVS to produce the recently adopted second version of the ICRF, ICRF2, and future plans to update the ICRF are also mentioned. This article is based on an interview with Chopo Ma, and it is available here.
2009.11.09: John Gipson gave an invited presentation "HF-EOP derived from VLBI" at the October 2009 IERS Workshop on EOP Combination and Prediction in Warsaw, Poland. He presented the results of an HF-EOP model derived from VLBI data through March 2009. This is an update of work originally done in 1996. Gipson compared the new model with the earlier results, with the more recent empirical models of Steigenberger et al.(derived from GPS data) and Sigrid (derived from VLBI data), and with semi-empirical models based on satellite derived tidal models. There is good agreement among the empirical models and among the semi-empirical models. For most tidal constituents, there is also agreement between the empirical and the semi-empirical models. However, for a few constituents, the empirical and the semi-empirical models differ at the many-sigma level.
2009.11.09: In early October, Chopo Ma, John Gipson and Dan MacMillan participated in a workshop sponsored by NSF, NASA, and USGS and organized by UNAVCO to discuss Long-Range Science Goals for the Geodesy Community. During the one day session, the participants separated into splinter groups to discuss science questions that can be addressed by geodetic techniques in various areas such as natural hazards. The output from the discussions is expected to help to identify emerging questions in geodesy and to identify the workforce and the equipment needed to investigate them.
2009.10.07: Benno Schmeing gave a demonstration of the proof-of-concept automated site tie monitoring system. The demonstration consisted of showing the actual operations in the field and giving a presentation about the theory and obtained results. The proof-of-concept demonstration was attended by approximately 20 participants, including representatives of NASA HQ, NOAA/NGS, JPL, and UNAVCO. Slides from the presentation are available here.
2009.10.07: Chopo Ma gave three presentations at the IAU General Assembly held in August 2009. In his capacity as the chair of the IERS Directing Board, Ma presented reports on the IERS at the IAU’s Commission 19 and Division I business meetings. These reports discussed the activities of various IERS groups (e.g., product centers and working groups), as well as recent IERS workshops and publications. At the Division I business meeting, Ma also presented a report on the work of the IERS/IVS Working Group for ICRF2, in his capacity as its chair. This report summarized the Working Group’s efforts towards defining the second realization of the International Celestial Reference Frame in time for the General Assembly to consider approving it in resolution B3. In the Working Group’s final contribution to ICRF2, Ma seconded resolution B3, which established ICRF2 as the fundamental celestial reference frame for astrometry and geodesy effective January 1, 2010.
2009.08.06: Benno Schmeing recently presented preliminary results of proof-of-concept studies for an automatic monitoring system of local site ties. The system is based on the usage of robotic total stations. Schmeing performed tests with a Leica TCA2003 total station on the local network of Goddard's Geophysical and Astronomical Observatory (GGAO) and the 5-m VLBI antenna at this site. Both the TCA2003 and the VLBI antenna can be controlled from a Matlab-coded control program. Running specific observational programs, Schmeing was able to collect data that indicate that the reference point of the VLBI antenna can be automatically determined with an accuracy of 1 mm or better. The PowerPoint presentation file plus additional support files can be downloaded here.
2009.08.03: David Gordon, Dan MacMillan, Chopo Ma and Sergei Bolotin have participated in a major update of the International Celestial Reference Frame at radio frequencies, as part of an international working group from the IVS (International VLBI Service for Geodesy and Astrometry) and the IERS (International Earth Rotation Service). The new realization, called ICRF2, contains the VLBI positions of 3414 compact radio sources with a noise floor level of approximately 40 micro-arc-seconds and an axes stability of approximately 10 micro-arc-seconds. This represents a roughly 5-fold improvement in the number of sources and the noise level, and a 2-fold improvement in the frame stability over the previous realization. An IERS Tecnical Note final draft has been completed. The ICRF2 will be presented to the IAU for approval this month. The new reference frame will have an impact on both geodesy and astrometry applications, including improved measurement of Earth orientation parameters, studies of the Earth's interior, basic astrometry, and spacecraft navigation. The draft technical note, IERS Technical Note 35, can be found at http://hpiers.obspm.fr/icrs-pc.
2009.06.10: "The Kinematics of Ny-Alesund from Space Geodetic Data" by H. P. Kierulf, R. Pettersen, D. S. MacMillan (GSFC), and P. Willis has been accepted for publication in the Journal of Geodynamics. This paper investigates the agreement between the geodetic technique (VLBI, GPS, and Doris) measurements at Ny-Alesund (Svalbard). The geodetic rates are compared with the rates of different geophysical processes in the Svalbard region.
2009.05.04: Dan MacMillan and Tonie van Dam (University of Luxembourg) presented “Comparison of Observation Level versus 24-hour Average Atmospheric Loading Corrections in VLBI Analysis” at the April 2009 EGU meeting. This presentation concluded that using observation level loading is marginally better than using the 24-hour average corrections, but using either method is acceptable for most purposes, which is important because GPS software currently does not have the ability to handle observation level loading. MacMillan was also a co-author of “Hourly Earth Rotation Parameters and Atmospheric Angular Momentum Functions for CONT08”, presented by J. Boehm (TU Vienna) et. al. This presentation compared hourly Earth rotation parameters from VLBI and GPS observations from a 15-day period in August 2008 to atmospheric angular momentum functions derived from hourly 4V data from the European Centre for Medium-Range Weather Forecasts. Other co-authors were D. Salstein (AER), P. Steigenberger (TU Munich), M. Schindelegger (TU Vienna), and H. Schuh (TU Vienna).
2009.05.01: John Gipson (GSFC VLBI) and Richard Ray (GSFC) presented “A New Model of Tidal EOP Variations from VLBI Data Spanning 30 Years” at the April 2009 EGU meeting. This update of work done in 1996 presented an improved empirical VLBI EOP model that used roughly three times as much VLBI data as in 1996. The model agrees well with semi-theoretical EOP models based on ocean tides. Gipson also attended a splinter meeting of the GGOS Bureau for Networks and Communications, at which he talked about the Terrestrial Laser Scanner Workshop hosted by the GSFC VLBI group in September 2008.
2009.04.14: A goal within the international astronomical community is the presentation of the second realization of the International Celestial Reference Frame (ICRF2) at the 2009 IAU General Assembly. Efforts are currently focused on selecting sources for the reference frame and developing a master solution that will be used to calculate the sources’ positions. At the 19th European VLBI for Geodesy and Astrometry (EVGA) Working Meeting, David Gordon presented “Preparations for the Next ICRF”, co-authored by Dan MacMillan, which described their work on selecting stable sources and testing various catalog solution options in support of the international efforts. Gordon, MacMillan, John Gipson, and Chopo Ma also attended a meeting of the IVS/IERS ICRF2 Working Group, which was held in conjunction with the EVGA Working Meeting and was chaired by Ma.
2009.04.14: Dan MacMillan presented a talk entitled “Recent Modeling Improvements in SOLVE Analysis”, co-authored by John Gipson, at the 19th European VLBI for Geodesy and Astrometry (EVGA) Working Meeting. This talk considered the effects of SOLVE analysis modeling improvements in the areas of the modeling of antennas’ thermal expansion and the modeling of the effect of the Earth’s troposphere on VLBI delays. The troposphere model improvements considered were the Vienna Mapping Function developed by the Institute of Geodesy and Geophysics of the Vienna University of Technology, elevation-dependent weighting, correlated station-dependent noise modeling developed by John Gipson (GSFC VLBI), and the slant-path delay model developed by Leonid Petrov as part of his work for the GSFC VLBI group. The antenna thermal expansion model uses antenna dimensions and expansion coefficients compiled for all of the VLBI antennas by Axel Nothnagel of the University of Bonn.
2009.04.14: John Gipson presented “Report of Working Group 4 on Data Structures” at the 19th European VLBI for Geodesy and Astrometry (EVGA) Working Meeting held March 24-25 at the University of Bordeaux. The report was a “straw-man” proposal from IVS Working Group 4 for the next-generation of VLBI data structures. The proposed structures have the following advantages: 1.) The data are stored in a format that is easily accessible across different languages and platforms; 2.) There is very little redundancy compared to the current scheme; 3.) The proposed scheme is flexible. Gipson also chaired a meeting of Working Group 4 that was held in conjunction with the EVGA meeting.
2009.04.14: A special session was held in conjunction with the EVGA Working Meeting to celebrate the 10th Anniversary of the International VLBI Service for Geodesy and Astrometry (IVS). By invitation, Tom Clark presented “Building the Geodetic VLBI Network”, a history of VLBI based on his personal recollections. The presentation focused heavily on the development of VLBI at GSFC, but it also mentioned recent developments within the IVS such as Mark-5A and e-VLBI technology.
2009.04.14: Tom Clark gave two presentations at the IVS VLBI 2010 Workshop on Future Radio Frequencies and Feeds held March 18-20 at the Wettzell Observatory. “Receivers for VLBI2010” discussed advances in receiver design, such as the new Haystack/GSFC receiver and the NRAO/EVLA receiver, as well as efforts to develop a new “digital” phase cal. “Useful RFI” proposed using Radio Frequency Interference for antenna calibration.
2009.03.06: During February, Chopo Ma, John Gipson, and Ed Himwich attended a meeting that was held at the Haystack Observatory and was devoted to VLBI2010 stations. In particular, the meeting focused on what can be done to make VLBI2010 stations less expensive to run and more robust. In addition to Haystack personnel, several people from NRAO participated remotely. There were several conclusions: 1.) You need a minimum of two people at remote sites. This is because you always need someone on call, and you need to provide coverage for vacations. In addition, for safety reasons, you need two people for some maintenance operations. 2.) The skill level of the on-site personnel can be lowered if you have someone who can remotely monitor and operate the equipment, the way the VLBA operates. 3.) To do this, you need to monitor and log as much information as possible. The remote operator needs to be able to see the status of all equipment on site, and to be able to troubleshoot remotely.
2009.02.09: The Journal of Geodesy has accepted “Precise Geodesy with the Very Long Baseline Array", which was written by a set of eight scientists that includes four current members and one recent member of the GSFC VLBI group. The paper reports on a 13 year program of geodetic measurements that used the VLBA with up to 10 additional antennas. The paper discusses the program’s goals and implementation, as well as the analysis of its data and several results. First author Leonid Petrov now works for ADNET Systems Inc. on another GSFC project, but he did part of his work on this paper while he was a member of the GSFC VLBI group. Co-authors from the GSFC VLBI group are David Gordon, John Gipson, Dan MacMillan and Chopo Ma. The remaining authors are Ed Fomalont (NRAO, Charlottesville), R. Craig Walker (NRAO, Socorro) and Claudia Carabajal (Sigma Space Corporation at GSFC).
2009.01.12: Dan MacMillan presented a poster, "Simulation Analysis of the Geodetic Performance of the Future VLBI2010 System", at the 2008 Fall AGU Meeting, with coauthors from the simulation group of the IVS VLBI2010 Committee. The poster summarized the group's investigation of strategies for improving geodetic performance, including optimized observing schedules, faster antenna slewing rates, and larger antenna networks. MacMillan’s coauthors included J. Gipson and seven other scientists representing the Geodetic Survey Division, Natural Resources Canada (B. Petrachenko), IGG, University of Technology Vienna (J. Böhm, A. Pany and J. Wresnik), MIT Haystack Observatory (A. Niell), and Onsala Space Observatory (R. Haas and T. Nilsson).
2009.01.12: In September 2008, an informal working group representing most of the space geodesy techniques met at the TLS workshop to address the problem of measuring and monitoring local site ties--that is, the ties between different techniques. At the 2008 Fall AGU meeting, John Gipson presented the group’s conclusions in “Report of Informal Working Group on Measuring and Monitoring Site Ties”. 14 authors from 10 institutions, including GSFC VLBI analysts Chopo Ma and Dirk Behrend, contributed to this report. By request, Gipson subsequently reprised the presentation at a splinter meeting in the AGU’s GGOS session.
2009.01.06: Dirk Behrend met with IVS Chair Harald Schuh (TU Vienna) and the editing team for the Progress Report of the IVS VLBI2010 Committee for an intensive, three-day editing session on December 11-13, 2008. During the three days, Schuh, Behrend, Bill Petrachenko (NRCan), and Brian Corey and Arthur Niell (both MIT Haystack Observatory) nearly finalized the report. The final version is expected to be available by the end of January 2009. The Progress Report constitutes a major step forward in defining the next-generation VLBI system.

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2008

2008.12.12: Ed Himwich gave two presentations during November. Himwich gave the first presentation, “DBE FS Considerations”, at the 5th US VLBI Technical Coordination Meeting held at NRAO in Socorro, New Mexico on November 17 and 18. This presentation covered interface issues between control programs, especially the Field System, and the new Digital Back-end and Mark 5C equipment. Himwich gave the second presentation, “Antenna and Instrumentation Considerations”, at the 8th RadioNet Engineering Forum Workshop held at the Centro Astronómico de Yebes in Yebes, Spain on November 24 and 25. This presentation covered interface issues between control programs and new antennas and instruments.
2008.11.07: On October 27-28, 2008, Chopo Ma chaired a meeting of the IERS Directing Board at USNO. One of the chief topics was the Call for Participation to the space geodesy services for input to ITRF2008 early next year. The VLBI input from IVS is essential for ITRF scale and the adjustment of UT1 and nutation. The need for uniform modeling was highlighted, e.g., the application of atmosphere loading, as well as the desire to remove technique-dependent effects such as antenna thermal changes. Some VLBI software will need to be modified and tested to meet these goals.
2008.10.07: Ed Himwich gave a presentation at the European VLBI Network’s Technical Operations Group Meeting held in Bologna, Italy on 9/22. “Field System Topics” discussed the current and future status of the software that drives most VLBI antennas. John Gipson (also of the GSFC VLBI group) and Jonathan Quick of the Hartebeesthoek Radio Astronomy Observatory were co-authors.
2008.10.07: Chopo Ma gave a presentation at the Journées 2008 meeting held from 9/22 through 9/24 in Dresden, Germany. “Present and Future Radio Reference Frames” discussed the implications of VLBI2010 for radio reference frames.
2008.10.07: Dirk Behrend and Ed Himwich attended the IVS Directing Board meeting held on 9/13 at the Dominion Radio Astrophysical Observatory in Penticton, BC, Canada. Behrend and Himwich gave reports for their respective positions as IVS’ Coordinating Center Director and Network Coordinator. Behrend also reported on the activities of the IVS Observing Program Committee.
2008.10.07: The GSFC VLBI group hosted the TLS workshop from 9/8 through 9/10 at Goddard. Chopo Ma, John Gipson and Dirk Behrend organized the workshop, and Ma and Behrend each chaired a session. The purpose of the workshop was to address the problem of measuring and monitoring local site ties--that is, ties between different geodetic techniques. Each technique measures the position of an "invariant reference point" (intersection of axis for VLBI and SLR; antenna phase center for GPS). For generation of the ITRF, these invariant points must be referenced to local geodetic markers. This is complicated because the reference points are often not directly accessible, and instead their positions must be inferred through surveying.
2008.08.13: Dirk Behrend attended the 2008 FGS (Forschungsgruppe Satellitengeodäsie) Workshop held in Bad Kötzting, Germany from July 16-18, 2008. He was the official IVS representative at the retirement ceremony that took place in the middle of the workshop at the Geodetic Observatory Wettzell for former IVS Chair and Wettzell Observatory Director Wolfgang Schlüter. Behrend gave a small speech for the occasion.
2008.07.22: Chopo Ma gave a presentation, "The Role and Future of VLBI in Geodesy", to the NRC Committee on National Requirements for Precision Geodetic Infrastructure on June 11 in Boulder, Colorado.
2008.06.30: Ed Himwich gave a talk called "Field System Considerations" at the 4th U.S. VLBI Technical Coordination Meeting, which was held May 29-30 at the Haystack Observatory. The talk presented issues concerning how the Field System, the software that drives VLBI antennas, will interact with new hardware that is being developed.
2008.06.13: The latest official GSFC VLBI ITRF quarterly solution (2008a, June 2008), quarterly intensive solution (Int23) and their associated earth orientation (eop) products can now be accessed through this web site's Data and Results page.
2008.05.20: Dan MacMillan presented a poster and co-authored a second poster and two oral presentations at the mid-April EGU General Assembly 2008. MacMillan's poster, "Improvement in Stability and Accuracy of the VLBI Reference Frame Realized with the Next Generation of VLBI Stations", discussed how a proposed network of next-generation (VLBI2010) stations would improve the VLBI terrestrial reference frame. His second poster, "The Geodetic Observatory at Ny-Ålesund: Different Techniques - Different Results?", presented with first author H. P. Kierulf (Norwegian Mapping Authority) and B.-R. Pettersen, discussed discrepancies in the analysis of the Norwegian Ny-Ålesund station seen among and within the VLBI, GPS and DORIS space geodetic techniques. The solicited oral presentation "Subdaily Earth Rotation Observed by GPS and VLBI", presented with first author P. Steigenberger (Institut für Astronomische und Physikalische Geodäsie, TU München) and others, compared GPS and VLBI estimates of high-frequency Earth rotation variations and discussed the combination of GPS and VLBI estimates. Finally, the oral presentation "Next Generation Global Geodetic Networks for GGOS", presented with first author E. C. Pavlis (JCET/UMBC and NASA GSFC) and others, presented simulation studies aimed at designing geodetic networks to support the Global Geodetic Observing System. The presentation especially focussed on developing a well-distributed SLR and VLBI network to minimize systematic errors in the International Terrestrial Reference Frame, a key GGOS product. Another GSFC VLBI scientist, Chopo Ma, was also a co-author of this presentation.
2008.04.23: Leonid Petrov gave a talk at the mid-April EGU General Assembly 2008. "Modeling Slanted Path Delay using Numerical 4D Models of the Atmosphere" proposed a new model for correcting space geodesy data for atmosphere path delay. The traditional model assumes a uniform and spherically symmetrical atmosphere at each observing site. The proposed model allows more accurate, non-uniform modeling through the application of 3D wave propagation differential equations to the refractivity field from NCEP Reanalysis and GEOS-5 4D numerical atmosphere models. It was demonstrated that using the output from the GEOS-5 model allows the prediction of the slanted path delay with an rms error in the range of 1-4 cm for elevation angles between 20 and 90 degrees. Using the slanted path delay in VLBI analysis improves the baseline length repeatability by 10%.
2008.04.16: Dirk Behrend and Chopo Ma participated in the 2008 GGOS Retreat, which took place from March 25-28, 2008 in Bertinoro, Italy at the Bologna Congress and Residential Centre. The retreat focused on the implementation of the GGOS strategy as described in the GGOS2020 Reference Document with particular emphasis on the organizational structure. Behrend chaired the breakout session on the Coordination Office, and Ma was the rapporteur for the breakout session on the Bureau for Networks and Communication.
2008.03.12: At the IVS 2008 General Meeting held in early March 2008, the GSFC VLBI group presented some of its recent work in four oral presentations and a poster. D. Gordon, C. Ma, J. Gipson, L. Petrov and D. MacMillan presented ``Selection of `Defining' Sources for ICRF2'', and Ma presented ``Some Challenges in Developing the Second ICRF''. Gipson, MacMillan and Petrov presented ``Improved Estimation in VLBI through Better Modeling and Analysis'', and MacMillan presented ``Simulation Analysis of the Geodetic Performance of Networks of VLBI2010''. Finally, Gordon, Ma, MacMillan, Petrov, Gipson and K. Baver presented a poster that gave an overview of the group's activities as an IVS Analysis Center.

Some GSFC VLBI group members also worked with members of other VLBI groups on five additional presentations concerning their collaborations within IVS. In conjunction with IVS Chair Harald Schuh (Institute of Geodesy and Geophysics at the Vienna University of Technology), D. Behrend co-authored two reports in his capacity as the IVS Coordinating Center Director about the IVS' recent activities and future plans. J. Gipson reported on the plans of the multi-national ``IVS Working Group IV on VLBI Data Structures'' in his capacity as the group's chair. D. MacMillan co-authored a presentation titled ``VLBI2010 Antenna Slew Rate Study'' (Petrachenko et. al.) with members of Natural Resources Canada and the Vienna University of Technology. Finally, D. Gordon and C. Ma co-authored a poster on ``Astrometry from VLBA Observations at 24 and 43 GHz'' (Lanyi et. al.), with members of the Jet Propulsion Laboratory, the U.S. Naval Observatory, the Labratoire d'Astrophysique de Bordeaux, the National Radio Astronomical Observatory, the National Aeronautics and Space Administration, and Remote Analysis Systems.
2008.01.18: Dan MacMillan made a poster presentation at the Fall AGU meeting in San Francisco on VLBI2010 simulations as part of the design of a future geodetic VLBI network. He also presented many of these results at the GGOS (Global Geodetic Observing System) Working Group on Networks and Communications meeting during the AGU week. The simulations showed that reference frame scale and EOP repeatabilities improve from (1) increasing network size and/or (2) increasing the data recording rate. The presentations also discussed results on the improvement of repeatabilities with increasing antenna slew rate, which is a critical design parameter for VLBI2010 antennas.
2008.01.04: Dirk Behrend prepared a presentation on IVS activities for the second half of 2007. The presentation was given by Chopo Ma at the GGOS (Global Geodetic Observing System) Working Group on Networks and Communications meeting on December 12 during the AGU week in San Francisco. The talk outlined the recent meetings, working group and committee activities, operational changes and improvements, and the first fringes from the VLBI2010 hardware development.

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2007

2007.12.27: The latest GSFC VLBI quarterly nuvel solution (2007dn) is now available on the 2007dn web page.
2007.11.28: The latest official GSFC VLBI ITRF quarterly solution (2007d, November 2007), quarterly intensive solution (Int22) and their associated earth orientation (eop) products can now be accessed through this web site's Data and Results page.
2007.11.14: On October 24, 2007, John Gipson made a presentation at a US-Norwegian bilateral science workshop at NOAA in Silver Spring, Maryland on improving UT1 predictions by reducing their latency using eVLBI to transfer the data. The time to produce UT1 measurements would be reduced from 2.25 days to 6 hours, and the uncertainty in predicted UT1 would be reduced from over 200 microseconds to about 40 microseconds. The GSFC VLBI group, together with the Norwegian Space Agency, is looking at a pilot program to demonstrate the feasibility of this approach using the Kokee-NyÅlesund baseline.
2007.11.06: Chopo Ma gave an invited talk at IAU Symposium 248, which was held at the Shanghai Observatory in mid-October. "The Second Realization of the ICRF with VLBI" updated and extended his September presentation at the Journées 2007 meeting, adding an overview of the roles various international groups are playing in developing the second ICRF realization for the benefit of the symposium's more general astronomical audience.
2007.10.10: During September, Chopo Ma presented two talks that reported the results of international efforts to enhance the ICRF (International Celestial Reference Frame). "Progress in the 2nd Realization of ICRF", presented at the Paris Observatory's Journées 2007 meeting, reported international progress towards the presentation of the second realization of the ICRF at the 2009 IAU General Assembly. Accomplishments include the establishment of a systematic program for monitoring astrometric sources and the development and improvement of information and tools, such as time series and source structure information to identify better "defining" sources for the reference frame. "Attributes of the ICRF", presented at the BIPM's IERS Workshop on Conventions, discussed the use of subsets of ICRF sources for various applications. The majority of the sources can be used for astronomical phase referencing. A small subset (the "geodetic catalog") is used for regular VLBI measurements that keep the ICRF and the ITRF (International Terrestrial Reference Frame) coupled. Another subset of sources is being developed for future use in spacecraft navigation at Ka band.
2007.10.10: During September John Gipson made a presentation to the IVS directing board about establishing a new working group, "Data Structures in VLBI". The board approved the formation of this group and appointed Dr. Gipson to chair the group. Dr. Gipson also participated in the Third VLBI2010 Working Meeting at the University of Bonn via conference call. Participants discussed scheduling strategies and issues.
2007.08.06: The latest official GSFC VLBI ITRF quarterly solution (2007c, July 2007), quarterly intensive solution (Int21) and their associated earth orientation (eop) products can now be accessed through this web site's Data and Results page.
2007.08.06: A major effort of the IVS is the design of the next generation VLBI system, VLBI2010. At the July 2007 XXIV IUGG General Assembly, part of the VLBI2010 development team, which includes four Goddard VLBI group members (Dirk Behrend, Tom Clark, John Gipson, and Dan MacMillan), presented a progress report in the form of a poster titled "VLBI2010". This poster summarized the recent advances and investigations in the VLBI2010 work: increasing the number of observations via faster antennas and improved scheduling algorithms, improving observation precision via broadband observing, determining optimal network configurations via Monte Carlo simulations, and improving source structure modeling via daily calculations of the structures from expanded data sets. A pdf copy of this poster is now available in the presentations section of the Papers and Presentations page .
2007.06.21: In April 2007, three GSFC VLBI analysts presented talks at the 18th Working Meeting of the EVGA (European VLBI Group for Geodesy and Astrometry). Pdf versions of these talks are now available in the presentations section of the Papers and Presentations page. John Gipson's "Incorporating Correlated Station Dependent Noise Improves VLBI Estimates" discusses his modeling of various types of correlated station dependent noise. Dan MacMillan's "VLBI2010 Simulations Using SOLVE" discusses simulations done for the VLBI2010 network design. Leonid Petrov's "Using Source Maps for Scheduling and Data Analysis: Approaches and Strategies" discusses his use of source structure maps to identify and evaluate candidate sources for geodetic processing. A proposal written by Petrov for updating the list of standard geodetic sources is also now available in the analysis section of the Memos page.
2007.05.16: Dirk Behrend (GSFC) and Heidi Johnson (Haystack) organized the IVS Technical Operations Workshop (TOW) that was held from April 30 through May 3 at Haystack Observatory. The TOW brought together about 60 people from stations, correlators, and the IVS Coordinating Center, as well as other operations-related persons. Many seminars, workshops, and lectures were given. Ed Himwich (GSFC) taught or co-taught classes about Pointing Models, the Field System, General Station Troubleshooting, and the Impact of Operations on Data Analysis. Behrend presented a lecture on the IVS.
2007.05.16: Chopo Ma presented a talk, "Ground Monitoring of Co-location Vectors", at the April 18 GGOS (Global Geodetic Observing System) Working Group on Ground Networks and Communications. Co-authored by Dirk Behrend (GSFC VLBI) and Erricos Pavlis (JCET), the talk was part of GGOS' effort to design a largely automated system to monitor local ties between various co-located space geodetic techniques. Specifically, this talk discussed the need for redundant monuments and pillars around each instrument, the realization of SLR/VLBI reference points by instrument motion, and the realization of GPS/DORIS reference points by physical geometry. The talk also summarized a recent presentation to the GSFC VLBI group of the Leica company's ideas for an automated VLBI/SLR station.
2007.05.07: Dan MacMillan presented three talks during April. MacMillan presented "Determination of Reference Frame Scale from VLBI" at the 2007 EGU (European Geosciences Union) General Meeting. This talk discussed sources of error that contribute to the VLBI scale and a resulting overall VLBI bias error that could explain much of the scale bias between VLBI and SLR in ITRF2005. MacMillan also presented "VLBI2010 Simulations Using SOLVE" at the 18th Working Meeting of the EVGA (European VLBI Group for Geodesy and Astrometry) and "VLBI Network Simulations" at the GGOS (Global Geodetic Observing System) Working Group on Ground Systems and Communication Meeting. These talks respectively discussed simulations done for the VLBI2010 network design and for the design of a global network for GGOS using collocated VLBI and SLR antennas.
2007.05.04: John Gipson presented his work on two topics during three April meetings. Gipson presented "Incorporating Correlated Station Dependent Noise Improves VLBI" as a poster at the 2007 EGU (European Geosciences Union) General Meeting and as a talk at the 18th Working Meeting of the EVGA (European VLBI Group for Geodesy and Astrometry). These presentations discussed Gipson's modeling of various types of correlated station dependent noise. Gipson also presented "Sked Issues" as a talk at the Second VLBI2010 Working Meeting of the IVS (International VLBI Service for Geodesy and Astrometry). This talk discussed the effects of varying antenna slew rates during the creation of experiment schedules through the Sked program.
2007.04.11: In early April, Dirk Behrend participated in a Director's meeting of the Federation of Astronomical and Geophysical Data Analysis Services at the ICSU (International Council for Science) in Paris. The participants discussed a possible restructuring of the federation.
2007.04.04: The latest official GSFC VLBI ITRF quarterly solution (2007b, March 2007), quarterly intensive solution (Int20) and their associated earth orientation (eop) products can now be accessed through this web site's Data and Results page.
2007.04.04: On March 20, Dr. John LaBrecque (NASA Headquarters), David Carter (GSFC SLR) and Dr. Chopo Ma (GSFC VLBI) presented the status of the Next Generation Satellite Laser Ranging (SLR) system to NASA Headquarters officials, including Dr. Michael Freilich, the recently appointed Director of NASA's Earth Science Division. Dr. LaBrecque presented a programmatic history and context of NASA's space geodesy efforts, Dr. Ma provided a technical overview of space geodesy and the importance of the geodetic networks to NASA, and Mr. Carter presented the status of SLR.
2007.03.22: Chopo Ma presented a talk at the February 2007 GGOS (Global Geodetic Observing System) Retreat. "IERS and GGOS", co-authored with Bernd Richter (Bundesamt für Kartographie und Geodäsie), discussed how the IERS (International Earth Rotation and Reference Systems Service) expects to contribute to and benefit from GGOS. Dr. Ma also attended the IVS (International VLBI Service for Geodesy and Astrometry) Directing Board Meeting in late February in his capacity as the board's IERS representative.
2007.03.16: Dirk Behrend presented two talks at the February 2007 GGOS (Global Geodetic Observing System) Retreat. "IVS View on GGOS: Contributions and Expectations", co-authored with Wolfgang Schlüter (Bundesamt für Kartographie und Geodäsie), discussed GGOS from the perspective of the IVS (International VLBI Service for Geodesy and Astrometry). "Ground Monitoring of Co-location Vectors" briefly summarized a conceptual design work for a co-location monitoring system to determine local tie information between the various space techniques in a largely automated fashion. Behrend also presented two reports at the February 24, 2007 IVS Directing Board Meeting. The reports summarized the activities of the IVS Coordinating Center and the IVS Observing Program Committee since the last board meeting.
2007.02.21: The Journal of Geodesy (JoG) has accepted and electronically published the article "Radio Source Instability in VLBI Analysis", by Dan MacMillan and Chopo Ma. This article will be part of the JoG Special Issue on VLBI and is available at: http://dx.doi.org/10.1007/s00190-007-0136-2. (A full-text download of the article requires an online subscription to the journal.)
2007.02.09: The Journal of Geodesy (JoG) has accepted and electronically published the article "The International VLBI Service for Geodesy and Astrometry (IVS): Current Capabilities and Future Prospects", by Wolfgang Schlüter (Bundesamt für Kartographie und Geodäsie) and Dirk Behrend (GSFC VLBI). This article will be part of the JoG Special Issue on VLBI and is available at: http://dx.doi.org/10.1007/s00190-006-0131-z. (A full-text download of the article requires an online subscription to the journal.)
2007.02.09: On February 5, the GSFC VLBI group hosted the 2007 East Coast VLBI meeting, which was attended by VLBI scientists from GSFC, the United States Naval Observatory and MIT's Haystack Observatory. The meeting focused on long-term goals and planning and on improving communications among the participating groups.
2007.01.24: The latest official GSFC VLBI ITRF quarterly solution (2007a, December 2006), quarterly intensive solution (Int19) and their associated earth orientation (eop) products can now be accessed through this web site's Data and Results page.
2007.01.12: Dan MacMillan presented "High Frequency Variations in Earth Rotation from VLBI Continuous Campaigns" at the Fall AGU Meeting in mid-December. Co-authored with David Salstein of Atmospheric and Environmental Research, Inc., this presentation discussed subdaily signals in Earth Rotation data from the CONT experiment campaigns, a series of two-week campaigns in which observations were made continuously.
2007.01.12: In early December, Ed Himwich presented "Field System Topics" at the European VLBI Network (EVN) Technical Operations Group (TOG) Meeting hosted by the National Institute for Astrophysics (INAF) of the National Research Council (CNR) of Italy. John Gipson (also of the GSFC VLBI group) and Jonathan Quick (Hartebeesthoek Radio Astronomy Observatory) were co-authors. The goal of the TOG meetings is the improvement of EVN station operations, and "Field System Topics" discussed new and future features of the Field System, the software that provides equipment control at VLBI stations. Himwich also presented a short tutorial on critical issues concerning the use of the "autoftp" and Mark 5 disk module label printing features.

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2006

2006.12.18: The latest GSFC VLBI quarterly nuvel solution (2006dn) is now available. 2006dn makes site evolution data available from our web site for the first time, and six velocity plots display new sites. More details are available at the 2006dn web page.
2006.11.09: Chopo Ma and Leonid Petrov attended the GRF2006 (Geodetic Reference Frames) meeting held by the International Association of Geodesy (IAG) from October 9 through October 14 in Munich. The focus of this meeting was an extended discussion of ITRF2005. Ma presented "The Effects of the Celestial Reference Frame on Geodesy", which was co-authored by Dan MacMillan, another member of the GSFC VLBI group. Petrov presented ``Empirical Earth Rotation Model: a Consistent Way to Evaluate Earth Orientation Parameters''. Petrov also displayed a poster, "Approach to Integrated Analysis of VLBI and SLR Observations", which was co-authored by four members of NASA GSFC's Planetary Geodynamics Laboratory--Frank Lemoine, Dave Rowlands, Despina Pavlis and Doug Chinn. While in Munich, Chopo Ma also attended the Global Geodetic Observing System (GGOS) workshop "Towards a Consistent Geodetic Foundation for Earth Observations", which focused on the integration of all geodetic methods and data, especially gravity. Ma presented "Inconsistencies in IAG Data, Products and Services at the 0.1 ppb Level", which was co-authored by Steve Kenyon of the National Geospatial-Intelligence Agency.
2006.10.12: The latest official GSFC VLBI ITRF quarterly solution (2006d, October 2006), quarterly intensive solution (Int18) and their associated earth orientation (eop) products can now be accessed through this web site's Data and Results page.
2006.09.26: GSFC VLBI personnel attended a series of meetings at MIT's Haystack Observatory in mid-September. Chopo Ma, John Gipson, Dirk Behrend, Ed Himwich and Dan MacMillan attended the first VLBI2010 (V2C) Working Meeting, to discuss improvement of the VLBI technique, especially the definition of specifications for the VLBI2010 antenna. MacMillan presented "VLBI2010 Simulations at GSFC Using Solve", his investigation of the sensitivity of baseline length repeatabilities to the variances of input atmospheric and clock delays and observation noise. Behrend and Himwich also attended the fifth International e-VLBI Workshop, and Behrend, Himwich and Ma attended the IVS Directing Board meeting held on September 16.
2006.09.26: Chopo Ma attended the VLBI2012 meeting held at the Institute of Applied Astronomy of the Russian Academy of Sciences from September 11 through September 14. Ma presented "The Uses of VLBI for Reference Frames", a discussion of VLBI's role in defining the terrestrial and celestial reference frames, and new developments in VLBI networks, instruments and observing programs that are necessary to continue to maintain these frames.
2006.09.19: The latest GSFC VLBI quarterly nuvel solution (2005en) can now be accessed through this web site's Data and Results page.
2006.03.03: In January , the GSFC VLBI group announced the suspension of operations at the Gilmore Creek Observatory (Gilcreek) as of the end of 2005. The suspension will allow U.S. funds to be reallocated for technical studies and hardware development leading towards the development of a "VLBI2010" system. The future installation of a new VLBI system at Gilcreek will remain an important goal.
2006.01.31: The latest official GSFC VLBI ITRF quarterly solution (2005e, December 2005), quarterly intensive solution (Int15) and their associated earth orientation (eop) products can now be accessed through this web site's Data and Results page.
2006.01.31: Several members of the GSFC VLBI group presented talks and posters at the 2006 General Meeting of the IVS (International VLBI Service for Geodesy and Astrometry), which was held in Concepcion, Chile from January 9 through January 11.

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2005

2005.12: The first phase of the renovated GSFC VLBI web site has been posted. This phase has concentrated on reorganization and reformatting of the core pages. The next phase will concentrate on renovation of the remaining pages.
2005.10.17: The GSFC VLBI group hosted a three day "East Coast" meeting in which Canadian and American VLBI scientists met to discuss ways to improve stages of VLBI processing ranging from scheduling through analysis. Participants included GSFC, USNO, the Haystack Observatory and Natural Resources Canada.
2005.09.12: The CONT05 campaign began. Fifteen days of continuous measurements were taken at an 11 site network that included two GSFC VLBI sites, Kokee Park (Hawaii) and Gilmore Creek (Alaska). GSFC VLBI scientists will analyze the data to support VLBI research and to make comparisons between VLBI and related techniques (GPS, SLR and DORIS).

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2004

Renovation of this site began in 2004.
The 2004 renovation focussed on defining and developing content and structure.
Our efforts in 2005 will finish this task and develop a more aesthetic presentation.

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