X-Band Sea Surface Coherence Time Inferred from Bi-static SAR Interferometry

Kurzfassung

Coherence time plays an important role in ocean surface observation by means of synthetic aperture radar (SAR). For X-band, the auto-correlation function of the backscatter from the sea surface has been predicted using models. Up to now there exist only few experimental data and an empirical analysis of the sea surface coherence time based on a larger amount of data is missing. In this paper we show how space-based bi-static SAR along-track interferometry is used for the first time to measure the auto-correlation function. We achieve this by statistical analysis of the interferometric scene coherence as a function of the along-track interferometric time lag, instead of indirect estimation from the Doppler bandwidth. We use many data acquisitions of opportunity for that purpose, thereby exploiting the diversity of along-track baselines between the two SAR sensors of the TanDEM-X satellite formation. The auto-correlation function is related to the temporal decorrelation, which is not directly observable. We extract this component by quantifying and compensating for all other sources of decorrelation that contribute to the observed coherence.