A joint method to retrieve directional ocean wave spectra from SAR and wave spectrometer data

Abstract

This paper proposes a joint method to simultaneously retrieve wave spectra at diff erent scales from spaceborne Synthetic Aperture Radar (SAR) and wave spectrometer data. The method combines the output from the two diff erent sensors to overcome retrieval limitations that occur in some sea states. The wave spectrometer sensitivity coeffi cient is estimated using an eff ective signifi cant wave height (SWH), which is an average of SAR-derived and wave spectrometer-derived SWH. This averaging extends the area of the sea surface sampled by the nadir beam of the wave spectrometer to improve the accuracy of the estimated sensitivity coeffi cient in inhomogeneous sea states. Wave spectra are then retrieved from SAR data using wave spectrometer-derived spectra as fi rst guess spectra to complement the short waves lost in SAR data retrieval. In addition, the problem of 180° ambiguity in retrieved spectra is overcome using SAR imaginary cross spectra. Simulated data were used to validate the joint method. The simulations demonstrated that retrieved wave parameters, including SWH, peak wave length (PWL), and peak wave direction (PWD), agree well with reference parameters. Collocated data from ENVISAT advanced SAR (ASAR), the airborne wave spectrometer STORM, the PHAROS buoy, and the European Centre for Medium-Range Weather Forecasting (ECMWF) were then used to verify the proposed method. Wave parameters retrieved from STORM and two ASAR images were compared to buoy and ECMWF wave data. Most of the retrieved parameters were comparable to reference parameters. The results of this study show that the proposed joint retrieval method could be a valuable complement to traditional methods used to retrieve directional ocean wave spectra, particularly in inhomogeneous sea states.

A Joint Method for Wave and Wind Field Parameter Inversion Combining SAR with Wave Spectrometer Data

“…Based on the merit and demerit of SAR and the wave spectrometer, Ren Lin et al used SAR and airborne Real Aperture Radar (RAR) to conduct a simulation study on detecting the direction spectrum with a low incidence angle, and the results show that RAR could detect waves that can be measured by SAR [19]. Ren Lin et al also proposed a method for retrieving the wave spectrum from SAR and wave spectrometer data [20].…”