Remote Sensing of Sea Surface Wave by Using CW X-Band Microwave Doppler Radar at Sagami-Bay

Abstract

Sea surface waves had been observed remotely by using a continuous wave (CW) X-band microwave Doppler radar at the off Hitatsuka of Sagami-bay in Japan. A new algorithm was applied to retrieve sea surface elevation from radar output Doppler signals. The sea surface waves observed by the microwave Doppler radar had been compared with the waves measured by a supersonic wave height meter. There were good correlations in both the wave height and the wave period between the waves observed by the microwave Doppler radar and that measured by a supersonic wave height meter. The correlation of wave heights was better than that of wave periods. The microwave irradiation width on sea surface does a role of space filter. It seems that the filtering effect is a kind of aliasing, the energy of short wavelength waves moves to low wave number region. The algorithm to retrieve a sea surface elevation is described by the relation of the water surface elevation and the orbital velocity of water particle on water surface that generated by water surface waves. A linear superposition method has been used to retrieve sea surface elevation. No empirical parameters are used in the algorithm, because the water surface elevation can be obtained from the water particle velocity on water surface by using the mathematical relation of the water surface elevation and the orbital motion of water particle. Water particle motion on sea surface is affected by sea surface wind, currents, and sea surface waves. Water particle motion generated by sea surface waves can be separated by the difference of the fluctuation scale of each physical process.