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Comparison between SAR atmospheric phase screens at 30' by means of ERS and ENVISAT data

Daniele Perissin(1)

(1) Politecnico di Milano, Via Ponzio 34/5, 20133 Milano, Italy

Abstract

SAR interferometry is theoretically capable of measuring millimetric displacements of radar targets that are coherently imaged by the radar at different times. However, phase delays induced by the water vapour content in the atmosphere can prevent from reaching the theoretical accuracy. Thus, atmospheric effects must be removed from interferograms in order to fully exploit the potentiality of InSAR. At the moment, no instrument can estimate the atmospheric delay with spatial resolution comparable to that of spaceborne SAR. The atmospheric delay can be estimated only from long series of SAR images (as in the Permanent Scatterers (PS) technique), by exploiting its statistical behaviour in space and time. The Atmospheric Phase Screen (APS) estimated by the PS technique gather then all phase delays that do not depend on the target elevation and on the adopted deformation model. Thus, APS can also include e.g. orbital errors or unknown (or not considered) spatially-dependent phase terms. In this work, for the first time, the estimated APS is compared to an independent measurement. In particular, the APS estimated from ERS data is analysed together with an APS retrieved with Envisat data at 30' time delay. The goal of the comparison is to highlight the effective dependence of the APS to the physical water vapour content of the troposphere. To this aim, the analysis is carried out by taking into account the wind effects, which can shift the estimated water vapour clouds in the time interval between the two acquisitions. Two methods will be considered: (1) a comparison between corresponding interferograms couples (ERS-ERS and Envisat-Envisat data at 30' in the same days) and (2) a comparison of APSs estimated in a coherent ERS-Envisat PS analysis (with a common ERS Master image). Interesting real data results will be shown over the city of Milan.

 

Workshop presentation

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry