Cross-validation of MERIS and ASAR-InSAR water vapor observations

Abstract

During the ERS-1 and ERS-2 missions, the application of synthetic aperture radar interferometry (InSAR) become known as a very important method for topographic mapping and high accuracy surface displacement measurements. Further investigations, however, showed that the expected accuracy could not be achieved in practice. It appeared that radiowave propagation heterogeneities through the atmosphere cause significant distortion to the observed signal and consequently to the derived topography and/or deformation signal. Inversely, it was shown that if topography is known and deformation is absent, the InSAR observations can be used to derive very accurate information on the state of atmosphere at the time of measurements. Due to the co-existence of MERIS (Medium Resolution Imaging Spectrometer) and ASAR (advanced synthetic aperture radar) on board of ENVISAT and the fact that their acquisitions can be collocated both in time and space, there are unique opportunities for complementary analysis. In this work we compare MERIS water vapor products and the integrated precipitable water vapor as observed with ASAR. Three complementary applications of the sensors are discussed. First, this is the correction of the atmospheric phase screen in InSAR products using the MERIS-derived water vapor signal. Second, we discuss the possibility for validating the MERIS water vapor product using InSAR data. Finally, we comment on the joint estimation of water vapor above and below the top of the cloud layers.