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 over
the 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 the
phase difference between two satellites radar images acquied at distinct overflight passes to produce
an 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, various
methods have been developed using empirical formulas based on the phase-elevation correlation or
global atmospheric models provided by the ECMWF. However, these methods are not well suited to
the context of Reunion Island, which features significant topography and highly variable atmospheric
conditions.
Here, we propose a GPS tomography algorithm specifically adapted to the island’s context in terms
of orography, spacial distribution of the GPS stations and inversion method, in order to reconstruct a
reliable 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 specific
SAR geometry.
Finally, local delays maps and the associated corrected interferograms at Reunion Island will
be compared to those obtained from the common approaches (empirical, global models) in order to
quantify the benefits of our approach.