Improving Tropospheric Corrections of InSAR Observations on Reunion Island using 3D GPS Water Vapor Tomography

Differential radar interferometry (dInSAR) enables to derive ground displacements maps all overthe globe. This method is particularly revelant on high active volcanoes such as the Piton de la Four-naise (Reunion Island) for monitoring volcanic unrest. The dInSAR method consists of computing thephase difference between two satellites radar images acquied at distinct overflight passes to producean interferogram showing cumulative displacements during the time period.Nevertheless, atmospheric variability between the txo epochs, especially water vapor in the tro-posphere, introduces a significant bias in the calculation of interferograms. To correct this, variousmethods have been developed using empirical formulas based on the phase-elevation correlation orglobal atmospheric models provided by the ECMWF. However, these methods are not well suited tothe context of Reunion Island, which features significant topography and highly variable atmosphericconditions.Here, we propose a GPS tomography algorithm specifically adapted to the island’s context in termsof orography, spacial distribution of the GPS stations and inversion method, in order to reconstruct areliable 3-D water vapor field above Reunion Island, (See corresponding abstract in Session G5.2).Hence, this water vapor field is then used to provide atmospheric corrections to individual Sentinel-1 interferograms by tracing each delays through the 3D tomographic grid according to the specificSAR geometry.Finally, local delays maps and the associated corrected interferograms at Reunion Island willbe compared to those obtained from the common approaches (empirical, global models) in order toquantify the benefits of our approach.