Using a Numerical Weather Model to Improve Geodesy

TL;DR

This study evaluates the use of Numerical Weather Models to improve atmospheric delay mapping in VLBI geodesy, showing significant improvements with hydrostatic functions but slight degradation with wet functions due to model resolution.

Contribution

It demonstrates that incorporating NWM data into VLBI analysis enhances baseline repeatability and reduces site position variations, especially with hydrostatic mapping functions.

Findings

Hydrostatic IMF improves baseline repeatability by up to 80% of the maximum expected.

Wet IMF slightly degrades baseline repeatability due to model resolution issues.

Hydrostatic mapping functions reduce residual harmonic site position variations.

Abstract

The use of a Numerical Weather Model (NWM) to provide in situ atmosphere information for mapping functions of atmosphere delay has been evaluated using Very Long Baseline Interferometry (VLBI) data spanning eleven years. Parameters required by the IMF mapping functions (Niell 2000, 2001) have been calculated from the NWM of the National Centers for Environmental Prediction (NCEP) and incorporated in the CALC/SOLVE VLBI data analysis program. Compared with the use of the NMF mapping functions (Niell 1996) the application of IMF for global solutions demonstrates that the hydrostatic mapping function, IMFh, provides both significant improvement in baseline length repeatability and noticeable reduction in the amplitude of the residual harmonic site position variations at semidiurnal to long-period bands. For baseline length repeatability the reduction in the observed mean square deviations achieves 80 of the maximum that is expected for the change from NMF to IMF. On the other hand, the use of the wet mapping function, IMFw, as implemented using the NCEP data, results in a slight degradation of baseline length repeatability, probably due to the large grid spacing of the NWM that is used.