Tropospheric delay estimates for InSAR derived from Vienna Mapping Function products

Michael Floyd, & Katherine A. Guns

Published September 10, 2023, SCEC Contribution #13274, 2023 SCEC Annual Meeting Poster #206 (PDF)

The Generic Atmospheric Correction Online Service for InSAR (GACOS) uses the method of Yu et al. (2017) to estimate tropospheric delay corrections to InSAR acquisitions. Their method includes estimating terms for the stratified portion of the troposphere, for which they use an exponential function of height, and an inverse distance weighting of residual delays, derived from tropospheric delays estimated from GNSS stations or, for GACOS currently, from numerical weather models, to estimate the turbulent portion. Accurate and consistent operational capability to correct the effect of tropospheric delay on InSAR is critical to the SCEC Community Geodetic Model products when studying low rates of motion and deformation. Here we present a potential improvement to the GACOS method by deriving the delay due to the stratified troposphere from physical equations rather than an empirical function, the coefficients for which are taken from the Vienna Mapping Function (VMF) products, which are derived from ray-tracing through the ECMWF numerical weather model through time. We then fix this stratified tropospheric term and estimate the turbulent part using the same inverse distance weighting method and a spline interpolation scheme, as opposed to GACOS's Iterative Tropospheric Decomposition (ITD) approach, which iterates to converge on coefficients for the two empirical terms. We see reductions in the differences (standard deviations) between the InSAR time series compared to GNSS time series projected into the InSAR line-of-sight over Southern California when applying our method compared to the GACOS correction, which improves the agreement between InSAR and GNSS in some areas while degrading it in others. The latter is observed particularly over regions of higher elevation so we conclude that our improved definition of the stratified tropospheric delay, and the application of VMF height-dependent mapping functions to the incidence angle of InSAR data, may be significant in this improvement. Our approach produces similar agreement between the two types of geodetic observations as produced by the method of Guns et al. (2022).

Key Words
InSAR, troposheric delay, GNSS

Citation
Floyd, M., & Guns, K. A. (2023, 09). Tropospheric delay estimates for InSAR derived from Vienna Mapping Function products. Poster Presentation at 2023 SCEC Annual Meeting.

Related Projects & Working Groups
SCEC Community Models (CXM)