Phase Calibration Of Interferometric Stacks
Mancon, Simone1; Monti Guarnieri, Andrea1; Giudici, Davide2; Tebaldini, Stefano1; Mapelli, Daniele2
1Politecnico di Milano, ITALY; 2Aresys srl, ITALY

Phase calibration has been discussed since the early SAR literature, but hardly implemented due to the difficulty in separating the various contributions. The aim of this work is to define a phase calibration method which allows to remove unwanted phase terms from each SLC (Single Look Complex). In particular, this work focuses on the phase artifacts due to: sensor orbit and DEM errors, atmosphere phase screen and stack coregistration, in case of TOPSAR acquisition mode.
Concerning the error in system geometry, the technique proposed in this paper exploits both the Phase Linking algorithm described in [1] and the multi-squint presented in [2]. In [2] the multi-squint technique is exploited to retrieve the phase screen, whereas we intend to use the same technique to recover system geometry (i.e.: orbit errors). So far, multi-squint has been applied only to estimate the phase artifacts of an interferometric pair (relative phase artifacts). We propose to apply multi-squint to an interferometric stack to estimate the phase artifacts on SLC. Eventually, the absolute position of sensor (orbit) and targets (DEM) for each SLC are retrieved (up to a roto-translation [6]). Moreover, the phase linking technique allows to identify the absolute phase artifacts from repeated revisits over both PS (Permanent Scatters) and distributed targets subjected to geometrical and temporal decorrelation. In order to derive the Atmospheric Phase Screen (APS) numerical weather models are used. In particular in this work we account for APS exploiting the European Centre for Medium-Range Weather Forecasts (ECMWF) zenith path delay as described in [3]. In the end third unwanted phase term is the TOPSAR stack coregistration artifacts.TOPSAR acquisition mode [4] is already investigated by TerraSAR-X [5] and will be implemented by Sentinel-1. TOPSAR mode features a forward steering of the antenna beam during image acquisition. This operation makes interferograms’ phase prone to artifacts due for example to a non perfect image coregistration. In this work we show how mis-registration artifacts are estimated as a phase fringe and simple removal.

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[3] Xiaoying Cong; Balss, U.; Eineder, M.; Fritz, T.; , "Imaging Geodesy-Centimeter-Level Ranging Accuracy With TerraSAR-X: An Update," Geoscience and Remote Sensing Letters, IEEE , vol.9, no.5, pp.948-952, Sept. 2012
[4] De Zan, F.; Guarnieri, A.M.; , "TOPSAR: Terrain Observation by Progressive Scans," Geoscience and Remote Sensing, IEEE Transactions on , vol.44, no.9, pp.2352-2360, Sept. 2006
[5] Prats, P.; Marotti, L.; Wollstadt, S.; Scheiber, R.; , "Investigations on TOPS interferometry with TerraSAR-X," Geoscience and Remote Sensing Symposium (IGARSS), 2010 IEEE International , vol., no., pp.2629-2632, 25-30 July 2010
[6] Stefano Tebaldini; Mauro Mariotti d'Alessandro; Francesco Banda; Claudio Prati; Fabio Rocca;, "Tomographic-quality phase calibration via phase center double localization" submitted to Geoscience and Remote Sensing Symposium (IGARSS) 2013.