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TerraSAR-X pixel localization accuracy: Approaching the centimeter level

The German satellites TerraSAR-X/TanDEM-X are high resolution imaging SARs with a resolution in the meter and even sub-meter range. The original product specification document stated an absolute geometric pixel localization accuracy in the same order of magnitude i.e. 1 meter. It was shown by several teams that this accuracy requirement is easily met and even surpassed [1] by the operational products. During the last years the remaining residual error sources could be further studied and attributed mainly to tropospheric delay variations [2] geodynamic effects such as solid earth tides [3] and plate tectonics to refraction in the ionosphere and to technical limitations in the satellite [4]. Our team investigated all these contributions developed correction and calibration methods and validated them in experiments with corner reflectors at different locations. Furthermore we explore novel applications of this high geolocation accuracy that range from classical earth surface displacement measurements to the localization of scatterers in 3D space with a precision comparable to GNSS. This paper provides a summary of latest measurement results of our globally distributed corner reflectors which show consistently a high accuracy better than 2 cm in range and azimuth. Furthermore we report on new developments concerning tropospheric correction using ECMWF and numerical weather models (WRF). Using the best available compensation techniques we can demonstrate accurate 3D localization of corner reflectors and of other objects. Current investigations aim to further improve the orbital accuracy to sub-centimeter level by improved modelling of air-drag and solar radiation pressure on the spacecraft.