A collocation approach for GNSS and InSAR combination, alternative 'tomographic' products and fusion in NWP models

Abstract

Global Navigation Satellite Systems (GNSS) and Interferometric Synthetic Aperture Radar (InSAR) are both subject to atmospheric delays. They can both sense the amount of water vapor in the atmosphere and be used as remote sensing techniques for its retrieval. Moreover, these techniques have complementary characteristics in terms of spatio-temporal resolutions. Indeed, GNSS and InSAR tropospheric products are dense in time and space, respectively. In this work, we use a collocation approach to combine these techniques with the aim to exploit their complementary characteristics for better atmospheric water vapor retrieval. The collocation software COMEDIE (Collocation of Meteorological Data for Interpretation and Estimation of Tropospheric Path Delays), developed at IGP-ETH, can combine GNSS zenith delays with InSAR slant delays. We display and discuss tropospheric products of the combination in terms of zenith delays with millimeter level accuracy. Furthermore, we use the collocation-estimated parameters to produce 'tomographic' like products, i.e. refractivity values. Finally, we assimilate our collocated products in the numerical weather prediction model WRF and investigate their impact. Our areas of investigation are the Alpine region in Switzerland, for which we use a set of simulated GNSS and InSAR measurements, and the URG (Upper Rhine Graben), where the GURN (GNSS Upper Rhine Graben Network) is located and InSAR data from Sentinel-1 are available. Some of the work presented is part of the AtmoWater project, a collaboration between ETH-IGP and several KIT institutes in the frame of better atmospheric water vapor fields' retrieval by GNSS and InSAR.