Measurement of directional spectrum of sea surface waves by using a microwave pulse Doppler radar with two fixed antennas

A sea surface measurement system using an X-band microwave pulse Doppler radar has been developed. This system can measure sea surface waves, a sea level and wind-driven sea surface currents simultaneously. It consists of main body of radar, two to four fixed antennas and data acquisition-processing equipment. The system measures Doppler signals of backscattering microwaves at several sea surfaces in each antenna irradiation direction for a period of time. Properties of each sea surface wave component such as a wave period, a wave height, a propagation direction and a local phase are obtained from the time series of Doppler velocity. Wave propagation direction is obtained from the change of wave phase in space (wave number) in each irradiation direction. The directional spectra of sea surface waves have been measured successfully. The propagation direction of a wave component that progresses within 45 degrees to the radar irradiation direction could be measured accurately. The wave propagation directions measured at off Hiratsuka in Sagami-bay are affected to a large degree by the configuration of Sagami-bay and distributed widely and discretely.