Merging SAR interferometry and GPS tomography for high-resolution mapping of 3D tropospheric water vapour

Microwave sensing of the atmosphere with GPS data, particularly using GPS tomography, provides a unique opportunity to measure the 3D state of the atmospheric water vapor, since it acquires data in a high temporal sampling. However, this technique requires a full domain coverage which is not fulfilled by GPS data, leading to an ill-posed conditioning only solved by constraints. SAR interferometry can be used to get integrated water vapor maps with high spatial resolution, but with a temporal frequency depending on the SAR acquisitions. In this work we describe a methodology to include integrated water vapor maps provided by SAR interferometry into the GPS tomography processing scheme. The differential water vapor spatial distribution occurred between the acquisition time of master and slave images is used to constrain the GPS tomography solution. Results are obtained over Lisbon area using GPS and ENVISAT-ASAR data and validated with regional radiosonde data.