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NASA NTRS2001

International VLBI Service for Geodesy and Astrometry

This volume of reports is the 2000 Annual Report of the International Very Long Base Interferometry (VLBI) Service for Geodesy and Astrometry (IVS). The individual reports were contributed by VLBI groups in the international geodetic and astrometric community who constitute the components of IVS. The 2000 Annual Report documents the work of these IVS components over the period March 1, 1999, through December 31, 2000. The reports document changes, activities, and progress of the IVS. The entire contents of this Annual Report also appear on the IVS web site at http://ivscc.gsfc.nasa.gov/publications/ar2000.

Vandenberg, Nancy R.↗
NASA NTRS2002

The VSOP-2 Space VLBI Mission

Following the success of the VLBI Space Observatory Program (VSOP), a next generation space VLBI mission, VSOP-2, is currently being planned. Higher observing frequencies, cooled receivers, increased bandwidths and larger telescope diameters will result in gains in resolution and interferometer sensitivity by factors of 10 over the VSOP mission. The use of phase-referencing by fast switching between a calibrator source and the target source is now being studied as this technique allows sources 50-150 times weaker to be observed depending on the frequency band. Such a capability would greatly enhance the VSOP-2 mission. Several other enhancements to the VSOP-2 mission are also presently under investigation including the VSOP-2 spacecraft operating at the same time as a US spacecraft to form what has come to be known as the iARISE (international ARISE) mission.

Hirabayashi, Hisashi↗
NASA NTRS2002

Structure Corrections in Modeling VLBI Delays for RDV Data

Since 1997, bimonthly S- and X-band observing sessions have been carried out employing the VLBA (Very Long Baseline Array) and as many as ten additional antennas. Maps of the extended structures have been generated for the 160 sources observed in ten of these experiments (approximately 200,000 observations) taking place during 1997 and 1998. This paper reports the results of the first massive application of such structure maps to correct the modeled VLBI (Very Long Baseline Interferometry) delay in astrometric data analysis. For high-accuracy celestial reference frame work, proper choice of a reference point within each extended source is crucial. Here the reference point is taken at the point of maximum emitted flux. Overall, the weighted delay residuals (approximately equal to 30 ps) are reduced by 8 ps in quadrature upon introducing source maps to model the structure delays of the sources. Residuals of some sources with extended or fast-varying structures improve by as much as 40 ps. Scatter of 'arc positions' about a time-linear model decreases substantially for most sources. Based on our results, it is also concluded that source structure is presently not the dominant error source in astrometric/geodetic VLBI.

Sovers, Ojars J.↗
NASA NTRS2002

The Goddard VLBI SINEX Files

The Goddard VLBI group generates SINEX files for individual 24-hr sessions and multiyear TRF solutions. Each 24-hr file includes the reduced normal matrix for the station positions, EOP, and EOP rates. A global Terrestrial Reference Frame (TRF) SINEX file has the reduced normal matrix for station positions and velocities but no EOP parameters. Both types of normal matrix are free from any datum constraints and are designed for combination solutions that will later apply the necessary datum constraints. The SINEX files also contain blocks that provide the constraints and covariance of well-defined 24-hr or global TRF solutions. These blocks are not yet part of the SINEX 2.0 specification. For the TRF solutions the Goddard VLBI group also generates the corresponding EOP time series. SINEX files and EOP time series are distributed through the IVS. The algorithms for generating the various blocks and the proper use of such SINEX files will be discussed.

Ma, Chopo↗
NASA NTRS2003

VLBI Data Longevity

The current cache of S/X-band geodetic/astrometric VLBI data accumulated since 1979 is approx.4.2 million observations and is increasing by approx.300,000 observations per year. The long time interval and access to all such VLBI data for re-analysis have contributed to their usefulness for the terrestrial and celestial reference frames, Earth orientation parameters, tidal and nontidal loading, and troposphere. While data access and integrity have been maintained through the Mark III data base system as storage devices and media have evolved, past transitions have been major projects. A new format and retention concept to ensure eternal archiving and access should make use of self-documentation, generalized media, network connectivity and multiple redundancy. Similarly permanent organizations or sequences of organizations are also necessary.

Ma, Chopo↗
NASA NTRS2004

International VLBI Service for Geodesy and Astronomy

This volume of reports is the 2003 Annual Report of the International VLBI Service for Geodesy and Astrometry (IVS). The individual reports were contributed by VLBI groups in the international geodetic and astrometric community who constitute the permanent components of IVS. The IVS 2003 Annual Report documents the work of the IVS components for the calendar year 2003, our fifih year of existence. The reports describe changes, activities, and progress of the IVS. Many thanks to all IVS components who contributed to this Annual Report. The entire contents of this Annual Report also appear on the IVS web site at http://ivscc.gsfc.nasa.gov/publications/ar2OO3

Vandenberg, Nancy R.↗
NASA NTRS2004

JPL VLBI Analysis Center IVS Annual Report for 2003

This report describes the activities of the JPL VLBI Analysis Center for the year 2003. We continue to do celestial reference frame, terrestrial reference frame, and spacecraft navigation work using the VLBI technique. Tracking the two Mars Exploration Rover spacecraft was the highlight for the year. We continued improvements in the first sub-milliarcsecond global celestial reference frames at K-band (24 GHz) and Q-band (43 GHz). The K-band catalog more than doubled in size from 108 to 230 sources.

Jacobs, Chris↗
NASA NTRS2004

Postseismic Transient after the 2002 Denali Fault Earthquake from VLBI Measurements at Fairbanks

The VLBI antenna (GILCREEK) at Fairbanks, Alaska observes in networks routinely twice a week with operational networks and on additional days with other networks on a more uneven basis. The Fairbanks antenna position is about 150 km north of the Denali fault and from the earthquake epicenter. We examine the transient behavior of the estimated VLBI position during the year following the earthquake to determine how the rate of change of postseismic deformation has changed. This is compared with what is seen in the GPS site position series.

MacMillan, Daniel↗
NASA NTRS2005

GSFC VLBI Analysis center

This report presents the activities of the GSFC VLBI Analysis Center during 2004. The GSFC Analysis Center analyzes all IVS sessions, makes regular IVS submissions of data and analysis products, and performs research and software development activities aimed at improving the VLBI technique.

Gordon, David↗
NASA NTRS1993

Prospects for VLBI Detection of Planets

The precision of astrometric VLBI measurements of radio-emitting stars has improved significantly during the past several years. For some stars whose radio flux density is only a few mJy the formal error and epoch-to-epoch scatter in position is approximately 200 - 600 micro-arcsec. The intrinsic signal/noise ratio in the data should allow a further order of magnitude improvement in astrometric precision as sources of systematic error are better understood and corrected. Wider bandwidth VLBI data recording systems currently under development will allow precisions of approximately 3 microarcsec if the measurements are limited by thermal noise. At this level planets with mass greater than or equal to 0.1 x M_(JUPITER) could be detected for the nearest radio-emitting stars.

Jones, D. L.↗
NASA NTRS1998

Geodetic VLBI Observations of EGRET Blazars

We present VLBI observations of the EGRET quasars 0202+149, CTA 26, and 1606+ 106, as well as additional analysis of VLBI observations of 1156+295 presented in Piner & Kingham (1997b).

blazars↗
NASA NTRS1995

Astrometry VLBI in Space (AVS)

This paper describes a proposal for a new space radio astronomy mission for astrometry using Very Long Baseline Interferometry (VLBI) called Astrometry VLBI in Space (AVS). The ultimate goals of AVS are improving the accuracy of radio astrometry measurements to the microarcsecond level in one epoch of measurements and improving the accuracy of the transformation between the inertial radio and optical coordinate reference frames. This study will also assess the impact of this mission on astrophysics astrometry and geophysics.

astrometry↗
NASA NTRS2006

International VLBI Service for Geodesy and Astrometry 2005 Annual Report

This volume of reports is the 2005 Annual Report of the International VLBI Service for Geodesy and Astrometry (IVS). The individual reports were contributed by VLBI groups in the international geodetic and astrometric community who constitute the components of IVS. The 2005 Annual Report documents the work of these IVS components over the period January 1, 2005 through December 31, 2005. The reports document changes, activities, and progress of the IVS. The entire contents of this Annual Report also appear on the IVS Web site at http://ivscc.gsfc.nasa.gov/publications/ar2005.

Behrend, Dirk↗
NASA NTRS2008

International VLBI Service for Geodesy and Astrometry 2007 Annual Report

This volume of reports is the 2007 Annual Report of the International VLBI Service for Geodesy and Astrometry (IVS). The individual reports were contributed by VLBI groups in the international geodetic and astrometric community who constitute the components of IVS. The 2007 Annual Report documents the work of these IVS components over the period January 1, 2007 through December 31, 2007. The reports document changes, activities, and progress of the IVS. The entire contents of this Annual Report also appear on the IVS Web site at http://ivscc.gsfc.nasa.gov/publications/ar2007.

Behrend, D.↗
NASA NTRS2008

The Global GNSS, SLR, VLBI, and DORIS Networks and their Support of GGOS: IGS+ILRS+IVS+IDS

The global network of the International GNSS Service (IGS), the International Laser Ranging Service (ILRS), the International VLBI Service for Geodesy and Astrometry (IVS), and the International DORIS Service (IDS) are part of the ground-based infrastructure for GGOS. The observations obtained from these global networks provide for the determination and maintenance of the International Terrestrial Reference Frame (ITRF), an accurate set of positions and velocities that provides a stable coordinate system allowing scientists ts to link measurements over space and time. Many of these sites offer co-location of two or more techniques. Co-location provides integration of technique-specific networks into the ITRF as well as an assessment/validation of the quality and accuracy of the resulting measurements. As of fall 2008, these networks consisted of 410 GNSS sites, 42 laser ranging sites, 45 VLBI sites, and 58 DORIS sites. This poster will illustrate the global coverage of these networks, highlighting inter-technique co-locations, and show the importance of these networks 60 the underlying goals of GGOS including providing the observational basis to maintain a stable, accurate, global reference frame.

Noll, Carey↗
NASA NTRS2009

International VLBI Service for Geodesy and Astrometry 2008 Annual Report

This volume of reports is the 2008 Annual Report of the International VLBI Service for Geodesy and Astrometry (IVS). The individual reports were contributed by VLBI groups in the international geodetic and astrometric community who constitute the components of IVS. The 2008 Annual Report documents the work of these IVS components over the period January 1, 2008 through December 31, 2008. The reports document changes, activities, and progress of the IVS. The entire contents of this Annual Report also appear on the IVS Web site at http://ivscc.gsfc.nasa.gov/publications/ar2008.

Behrend, Dirk↗
NASA NTRS2009

Estimating Accurate Relative Spacecraft Angular Position from DSN VLBI Phases Using X-Band Telemetry or DOR Tones

At present spacecraft angular position with Deep Space Network (DSN) is determined using group delay estimates from very long baseline interferometer (VLBI) phase measurements employing differential one way ranging (DOR) tones. As an alternative to this approach, we propose estimating position of a spacecraft to half a fringe cycle accuracy using time variations between measured and calculated phases as the Earth rotates using DSN VLBI baseline(s). Combining fringe location of the target with the phase allows high accuracy for spacecraft angular position estimate. This can be achieved using telemetry signals of at least 4-8 MSamples/sec data rate or DOR tones.

x-band telemetry↗