A lightweight Spectrasat concept for global ocean wave monitoring

For more than two decades, spaceborne SAR has been advocated as a practical means of monitoring directional ocean wave spectra. Seasat, ERS-1 and -2, JERS-1, Almaz, the Shuttle Imaging Radars A, B, and C, and most recently Radarsat have all carried SARs that have been or are being used to monitor the spatial evolution of wind-driven waves, with the hope (or promise) of improving storm prognosis. Yet it has been well known for more than a decade that all the higher altitude platforms (Seasat, ERS-1 and -2, JERS-1, and Radarsat) suffer serious imaging problems caused by the moving ocean scatterers, which effectively act to filter along-track waves shorter than about 300 m wavelength. Nevertheless, substantial effort has been expended toward the problem of understanding the SAR transfer function, and toward optimally assimilating the SAR wave estimates into operational wave forecast models. Unfortunately, these efforts at assimilation are unlikely to yield their intended results (i.e., improved wave forecasts) without a much lower altitude operational SAR platform. The authors present the details of a possible small, low-altitude satellite remote sensing system.