IVS 2007 Annual Report
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U.S. Naval Observatory VLBI Analysis Center

David A. Boboltz, Alan L. Fey, Jennifer L. Bartlett, Zachary Dugan, Kerry A. Kingham, David M. Hall

United States Naval Observatory

Abstract:

This report summarizes the activities of the VLBI Analysis Center at the United States Naval Observatory for calendar year 2007. Over the course of the year, Analysis Center personnel analyzed biweekly 24-hour experiments with designations IVS-R1 and IVS-R4 for use in-house and continued timely submission of IVS-R4 databases for distribution to the IVS. During the 2007 calendar year, the USNO Analysis Center produced three periodic global Terrestrial Reference Frame (TRF) solutions with designations usn2007a, usn2007b, and usn2007c. Earth orientation parameters (EOP) based on these solutions, updated by the latest 24-hour (IVS-R1 and IVS-R4) experiments, were submitted to the IVS.

Other activities in the 2007 calendar year included the generation of a new Sinex solution, usn2007b, and the continued submission of Sinex files based on new 24-hour experiments to the IVS. In support of the Celestial Reference Frame (CRF), Analysis Center personnel continued a program designed to increase the sky density of ICRF sources, especially in the southern hemisphere. Activities included scheduling, analyzing and submitting databases for IVS-CRF experiments and the production of global CRF solutions designated crf2007a, crf2007b, and crf2007c. In addition, Analysis Center personnel performed research into the next generation ICRF-2 and a future high-frequency reference frame based on the VLBA K/Q-band experiments. Activities planned for the 2008 calendar year include the continued production of EOP/TRF/CRF global solutions and continued research into future reference frames.

1. Introduction

The USNO VLBI Analysis Center is supported and operated by the United States Naval Observatory (USNO) in Washington, DC. The primary services provided by the Analysis Center are the analysis of 24-hour experiments, the production of periodic global Terrestrial Reference Frame (TRF) and Celestial Reference Frame (CRF) solutions, and the submission to the IVS of intensive (EOP-I) and session-based (EOP-S) Earth orientation parameters based on USNO global TRF solutions. Analysis Center personnel maintain the necessary software required to continue these services to the IVS including periodic updates of the GSFC CALC/SOLVE software package. In addition to operational VLBI analysis, USNO personnel engage in research aimed at developing the next generation ICRF. Information on USNO VLBI analysis activities may be obtained at:

http://rorf.usno.navy.mil/vlbi/.

2. Current Analysis Center Activities

2.1 Experiment Analysis and Database Submission

During the 2007 calendar year, personnel at the USNO VLBI Analysis Center continued processing of 24-hour (IVS-R1 and IVS-R4) experiments for use in internal USNO global TRF and CRF solutions. USNO is also responsible for the timely analysis of the IVS-R4, and the resulting databases are submitted within 24 hours of correlation for dissemination by the IVS. In addition, Analysis Center personnel continue to be responsible for the analysis and database submission for the periodic IVS-CRF experiments. The primary goal of these experiments is the densification of ICRF sources in the southern hemisphere. In 2007, USNO scheduled and analyzed 15 CRF experiments including IVS-CRF43 through IVS-CRF48, CRF-S11, and IVS-CRDS34 through IVS-CRDS41. The analyzed databases were submitted to the IVS. In the 2007 calendar year, Analysis Center personnel also continued analyzing IVS intensive experiments for use in a USNO EOP-I time series.

  
Figure 1: Distribution of RMS delay and rate for the 3666 24-hour sessions in the latest USNO global TRF/EOP solution usn2007c.
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2.2 Global TRF Solutions, EOP and Sinex Submission

USNO VLBI Analysis Center personnel continued to produce periodic global EOP/TRF solutions (usn2007a, usn2007b and usn2007c) over the course of the 2007 calendar year. All USNO global EOP/TRF solutions including the most recent solution may be found at:

http://rorf.usno.navy.mil/solutions/.

An example of the information available on the Web site is shown in Figure 1. It shows the distribution of the RMS delays and rates for the 3666 24-hour experiments in the latest USNO solution, usn2007c. Session-based Earth orientation parameters derived from our solutions are routinely compared to those derived from GSFC periodic TRF solutions and to the IERS-C05 time series prior to submission to the IVS.

Analysis Center personnel continued to produce an EOP-S series based on the global TRF solutions and continuously updated by new data from the IVS-R1/R4 experiments. This updated EOP-S series is submitted to the IVS twice weekly within 24 hours of experiment correlation and is included in the IERS Bulletin A. Analysis Center personnel also produced an updated Sinex series usn2007b and continued to submit Sinex format files based on the 24-hour VLBI sessions.

In addition to EOP-S and Sinex series, USNO Analysis Center personnel continued to produce and submit to the IVS an EOP-I series based on the IVS intensive experiments.

2.3 Celestial Reference Frame

During the 2007 calendar year, Analysis Center personnel continued work on the production of global CRF solutions for dissemination by the IVS including crf2007a, crf2007b, and crf2007c. These solutions are routinely compared to the current ICRF and are available through the previously mentioned Web site: http://rorf.usno.navy.mil/solutions/.

During 2007, Analysis Center personnel performed a variety of CRF related research activities with the purpose of improving the present ICRF and preparing for future VLBI-based reference frames. These activities included: the continued densification of the ICRF in the southern hemisphere through IVS-CRF and ATNF/USNO observations, investigations into the costs and benefits of adding the sources from the VLBA Calibrator Survey (VCS) to the CRF, time series analysis of source position variations for the purpose of source classification for ICRF-2, and production of a CRF based upon the 10 VLBA K-band experiments recorded as part of the K/Q-band high-frequency reference frame program. As an example, Figure 2 shows the sky distribution of the 266 sources with three or more delay observations at K-band (24 GHz). Although there have been only 10 K/Q-band experiments recorded from 2002 to present, the number of observations is 82,354, and the weighted RMS of the differences between the K-band CRF and the ICRF source positions is only a factor of $\sim$2.8 times worse than our latest X/S-band CRF with over 5 million observations.

  
Figure 2: The distribution of the 266 sources with three or more observations at K-band (24-GHz) plotted on an Aitoff equal area projection of the celestial sphere. Observations were taken with the VLBA under the K/Q-band high-frequency reference frame program.
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3. Staff

The staff of the VLBI Analysis Center is drawn from individuals in both the Astrometry and Earth Orientation departments at the U.S. Naval Observatory. The staff and their responsibilities are as follows:

Name Responsibilities
David Boboltz Periodic global TRF solutions and comparisons, Sinex generation and submission, Web page administration, VLBI data analysis.
Alan Fey Periodic global CRF solutions and comparisons, CRF densification research, Web page administration, VLBI data analysis.
Jennifer Bartlett VLBI data analysis, EOP and database submission.
Zachary Dugan VLBI data analysis, EOP and database submission.
Kerry Kingham Correlator interface, VLBI data analysis.
David Hall Correlator Interface, VLBI data analysis.

4. Future Activities

For the upcoming year January 2008-December 2008, USNO VLBI Analysis Center personnel plan to accomplish the following activities:


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IVS 2007 Annual Report