Large‐and small‐scale spatial evolution of digitally processed ocean wave spectra from SEASAT synthetic aperture radar

Abstract

Precision digitally processed and corrected synthetic aperture radar (SAR) image spectra along a large portion of SEASAT orbit 1339 (September 28, 1978) have revealed a number of unique potentials, but also some substantial limitations of spaceborne SAR for global ocean wave monitoring. SAR appears to be capable of monitoring the spatially evolving ocean wave number spectrum with high statistical reliability. The large‐scale (few hundred kilometer) spatial evolution of the spectrum is generally consistent with the location (in time and space) of wave‐generating sources, even when multiple wave systems are present. On a more local scale of just a few tens of kilometers, the nearshore wave number spectrum responds to local depth changes but is too noisy to respond reliably to local current changes. The SEASAT SAR was severely restricted in its ability to sense azimuthtraveling (along‐track) waves in high sea states. Azimuth waves corresponding to ocean wavelengths shorter than about 200 m were either undetected or severely attenuated in the higher sea states (Hs≥2 m); azimuth waves shorter than 100 m are not detectable in even the lowest sea states. Moreover, there is a tendency for attenuated wave systems to be shifted toward the range direction. This effect will significantly impede studies of spatial evolution of SEASAT SAR spectra without some additional correction strategy.