Global tracking of swell with complex ERS-2 wave mode data

Complex synthetic aperture radar (SAR) data acquired by the European remote sensing satellite ERS-2 are used to analyze the propagation of swell on a global basis. The study is based on complex SAR wave mode imagettes, which were processed from ERS-2 SAR raw data using the DLR BSAR processor. Complex imagettes allow to apply the so called cross spectra technique globally for the first time. In contrast to conventional SAR intensity images, cross spectra provide information on ocean wave propagation without 180° ambiguity. A test data set of three weeks of complex imagettes (≈36000) is used to measure ocean swell. Distribution of swell is studied based on maps showing swell direction, wave height and wavelength. Temporal swell dynamics is analyzed using data acquisitions with small spatial distance and a time gap of ≈12 h. Apart from providing information on ocean swell the study is a preparation for the coming ENVISAT era where cross spectra will be a standard product of the European Space Agency (ESA)