Estimation of tropospheric biases in SLR to Swarm, and LAGEOS satellites

Satellite Laser Ranging (SLR) is the only one space geodetic technique in which troposphere correction is calculated based on in situ measurements (pressure, temperature, and humidity) and used in the least square adjustment process as a fixed value measured at the epoch of observation.  In the past few years, we observe that the use of malfunctioning barometers for some of the SLR stations significantly affects the SLR-based global geodetic parameter estimates, such as station coordinates, geocenter coordinates, and terrestrial reference frame scale. Thus, we examine different handling of the SLR range tropospheric delay to LAGEOS by analysing the a priori zenith total delay from the standard Mendes and Pavlis (2004) model with a corresponding mapping function, the estimated tropospheric correction, and the range bias parameter. Moreover, we conduct a simulation study of artificial pressure bias, investigating the capability of tested approaches to properly reconstruct the tropospheric error. The new approach based on the estimation of the troposphere delay correction for SLR solutions, which is also widely used in microwave techniques, explicitly demonstrates more suitable handling of errors affecting the SLR station than solutions based on estimation of range biases.

The progress in precise orbit determination of low Earth orbiter (LEO) satellites using GPS demands improvements of the SLR procedures considering their orbit validation, determination of station coordinates, and global geodetic parameters from SLR to LEOs solutions. Within this study, we also consider including the proper handling of range errors in SLR to LEOs. We test solutions incorporating the estimation of tropospheric biases with and without horizontal gradients, range biases, and station coordinate corrections in an example of the SLR observations to LEO Swarm satellites. We discuss the values of estimated corrections and their impact on the solution quality, and dependency of residuals to different measurement conditions, such as elevation angle, azimuth angle, station-satellite distance, or satellite view from a station. Estimating tropospheric biases once-per-day and horizontal gradients, absorbs elevation- and azimuth-dependent errors, provides a reduction of solution statistics, and dependency of SLR residuals for almost all used SLR stations.