High resolution satellite measurements of coastal wind field and sea state

Abstract

Methods to derive wind speed and the sea state by simple empirical models from SAR data are presented and applied for use in high resolution numerical modeling for coastal application. The new radar satellite TerraSAR-X (TS-X) images the sea surface with a high resolution up to 1m. So not only the wind information, integrated sea state parameters but also individual ocean waves with wavelengths down to 30m are detectable. Two-dimensional information of the ocean surface retrieved using TS-X data is validated for different oceanographic applications: derivation of fine resolved wind fields (XMOD algorithm) and integrated sea state parameters (XWAVE algorithm). Both algorithms are capable to take into account fine-scale effects in the coastal areas. The wind and sea state information retrieved from SAR data are applied as an input for a wave numerical spectral model (wind forcing and boundary condition) running at fine spatial horizontal resolution of 100m. Results are compared to collocated buoy measurements. Studies are carried out for varying wind speed and comparison against wave height, simulated using original TS-X derived wind, show sensitivity of waves on local wind variation and thus the importance of local wind effects on wave behaviour in coastal areas. Examples for the German Bight, North Sea are shown. The TS-X satellite scenes render well developed ocean wave patterns of developed swell at the sea surface. Refraction of individual long swell waves at a water depth shallower than about 70m is caused by the influence of underwater topography in coastal areas is imaged on the radar scenes. A technique was developed for tracking of wave rays depending on the change of swell wavelength and direction. We estimate the wave energy flux along the wave tracks from deep water to the coastline based on SAR information: wave height and wave length are derived from TS-X data