ESTIMATION OF DIRECTIONAL SURFACE-WAVE SPECTRA FROM A TOWED RESEARCH CATAMARAN

During the High-Resolution Remote Sensing Main Experiment (1993), wave height was estimated from a moving catamaran using pitch-rate and rol l-rate sensors, a three-axis accelerometer, and a capacitive wave wire . The wave spectrum in the frequency band ranging roughly from 0.08 to 0.3 Hz was verified by independent buoy measurements. To estimate the directional frequency spectrum from a wave-wire array, the Data-Adapt ive Spectral Estimator is extended to include the Doppler shifting eff ects of a moving platform. The method is applied to data obtained from a fixed platform during the Riso Air-Sea Experiment (1994) and to dat a obtained from a moving platform during the Coastal Ocean Processes E xperiment (1995). Both results show that the propagation direction of the peak wind waves compares well with the measured wind direction. Wh en swells and local wind waves are not aligned, the method can resolve the difference of propagation directions. Using the fixed platform da ta a numerical test is conducted that shows that the method is able to distinguish two wave systems propagating at the same frequency but in two different directions.