Impact of satellite wave measurements on wave modelling

Through the launch of ocean observing satellites, wave modellers are now for the first time receiving detailed wave data on a global, continuous basis. This can be expected to have a profound impact on wave modelling. The first us ocean satellite SEASAT demonstrated in 1978 that wave heights could be accurately measured with a radar altimeter and that a SAR (synthetic aperture radar) was capable of imaging ocean waves. Unfortunately, SEASAT failed after three months, and further satellite wave measurements were not made until the radar altimeter aboard GEOSAT was put into orbit in 1985. This changed with the launch of the first European Remote Sensing Satellite ERS-1 in July 1991. Since then, both radar altimeter and SAR wave data have been produced again globally in a continuous, near-real-time mode (cf. table 1.1).

Even before satellite wave data became available on a quasi-operational basis, the recognized potential of these data had a strong influence on wave modelling. One of the principal motivations for developing the third generation wave model WAM was to provide a state-of-the-art model for the assimilation of global wind and wave data from satellites for improved wind and wave field analysis and forecasting. Prior to the development of the WAM model, wave modellers had available only first and second generation wave models. The former were known to be based on incorrect physics, while the latter contained essentially correct physics but were restricted numerically through an artificial separation of the spectrum into a wind sea component of prescribed spectral shape and a swell spectrum, with rather arbitrary parametrizations of the coupling between the two spectral regimes.