Analysis of Two-dimensional Sea Surface Elevation Fields Using Spaceborne and Ground-Based Remote Sensing Techniques

Abstract

This study, which is performed in the framework of the European Project MAXWAVE, deals with both theoretical aspects of extreme waves description as well as new techniques to observe these waves using different remote sensing techniques. The final goal is to improve the understanding of the physical processes responsible for the generation of extreme waves and to identify geophysical conditions in which such waves are most likely to occur. Space borne Synthetic Aperture Radar (SAR) is capable to provide simultaneous high resolution measurements of ocean waves on a global scale. Due to their all weather capability SAR is still the only instrument providing directional information on waves on a continuous basis. In the present study a reprocessed data set of complex SAR images acquired by the European Remote Sensing satellite ERS-2 is used to estimate different ocean wave parameters. A new method is presented to derive two dimensional sea surface elevation fields from complex SAR data. The method allows to analyse wave fields in more detail than conventional SAR wave measurement techniques, which only estimate the wave spectrum, i.e. second order moments of the wave field. The technique provides parameters like maximum to significant wave height ratios and wave steepness. Global maps and statistics of the new parameters are presented. Complementing the SAR measurements a nautical radar operating at X-band near grazing incidence (WaMos II), which can be operated from both ships and ground based stations, is used to analyse the time-space structure of the wave field using temporal sequences of radar images. The data are, e.g. used to investigate the propagation of wave groups.