TRF Accuracy Improvement from Better Atmosphere Modeling for VLBI and GPS
Abstract
Significant improvements in the Terrestrial Reference Frame (TRF) have been attained through better modeling of the atmosphere. Each advance in mapping function for the azimuthally symmetric component of the troposphere has resulted in better definition of the local vertical component of the geodetic measurements and thus in the scale of the TRF. Studies of the azimuthally asymmetric contribution of the atmosphere to the delay model have indicated the need to estimate the magnitude and direction of such an effect. Incorporation of a gradient model has improved the accuracy of the horizontal component of site positions and has reduced systematic declination-dependent errors in the Celestial Reference Frame. A major step in modeling the azimuthally symmetric atmosphere was the separation into hydrostatic and wet components, based on recognition that the different vertical distributions require different mapping functions for the best modeling accuracy. Implementation of such a model is possible because the hydrostatic zenith delay can be calculated accurately apriori from surface pressure measurements, leaving the wet delay to be estimated. As the precision of geodetic GPS and VLBI measurements has improved, so has the need for better modeling of the azimuthally asymmetric contribution of the atmosphere. We have developed a means of correcting for the hydrostatic gradient using information from a global numeric weather model, thus allowing the estimation of the wet gradient with its significantly different mapping function. The data set required for the hydrostatic gradient information is the same as that to be used for a new time- and site-dependent azimuthally symmetric hydrostatic mapping function. We will describe the derivation and give the results of testing the new hydrostatic gradient model with VLBI data. The use of a re-analysis of the global weather data (e.g., by the Goddard Space Flight Center Data Assimilation Office) will ensure that the atmosphere model contribution to the TRF is consistent over the entire span of VLBI data.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2001
- Bibcode:
- 2001AGUFM.G32A..08N
- Keywords:
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- 1229 Reference systems;
- 1247 Terrestrial reference systems;
- 1294 Instruments and techniques