Tropospheric delay estimation and analysis using GPS and SAR interferometry

Abstract

Spatially localized refractivity variations, mainly due to water vapor, are a major source of error in high-precision positioning techniques such as GPS and SAR interferometry. Refractivity induced delay variations can be misinterpreted as, e.g., crustal deformation signals or positioning biases. In this study, signal delay estimates based on SAR observations and simultaneous GPS time series are quantitatively compared. Wind speed and wind direction estimates are used to relate the temporal zenith delays derived from GPS with the spatial slant delays observed by SAR interferometry, assuming a static refractivity distribution transported by the wind. Five case studies show significant correlation between both techniques, mainly limited by the GPS epoch length, zenith averaging, and the degree of similarity in wind direction during the two SAR acquisitions. RMS differences varied between 2 and 10 mm, while the total delay variability spanned 15–60 mm. The results show that it can be possible, under suitable atmospheric circumstances, to approximate the amount of delay variation with wavelengths >5 km in a strip of a SAR interferogram using GPS, wind speed, and wind direction measurements.