Spatial domain techniques to derive sea state parameters from ERS and ENVISAT SAR imagettes

So far mainly one dimensional wave measurements (e.g. buoy time series) have been collected and analyzed. Using new measurement techniques, like Synthetic Aperture Radar (SAR) based ones (e.g. using ERS-1/2 and ENVISAT SAR Imagettes), it is now possible to retrieve two dimensional sea surface elevations. New analysis techniques have been found to examine these data. As in time series wave crests and troughs follow each other simply as alternating maximum and minimum points, in two dimensions the situation is more complicated. A so-called ´Spider´ algorithm has been developed creating an assignment of corresponding crest and trough points on a two dimensional sea surface. This allows examination of individual wave parameters like individual wave height or steepness to be compared with global and statistical ones on the surface itself, like significant wave height and sea surface gradient. In addition, grouping parameters can be generalized in the spatial domain. Image analysis also allows parameters not available in one dimension like the crest/trough lengths. For statistical examinations, these parameters have been calculated on some 34,000 SAR imagettes, globally distributed in a 3 week period in the southern winter.