Microwave measurement of sea surface velocities from pier and aircraft

Illumination of the ocean surface with coherent microwave radiation allows one to measure the mean velocity of the surface area via Doppler shifts. If the illuminated area is small compared to dominant ocean waves then in addition to mean currents, fluctuating surface velocities due to the waves can be detected. In this paper we present such measurements made during the ARSLOE experiment both from the CERC Field Research Facility pier at Duck, N.C. and from aircraft flying over the ocean east of Duck. Time averaged velocities determined from microwave Doppler measurements from the pier showed good agreement with currents measured by following dye tracers. Fluctuating parts of these signals were used to infer wave height spectra which were compared with spectra from standard Baylor gauges and found to agree well. Similar Doppler shift fluctuations were observed in signals obtained from aircraft measurements and were shown to agree well with surface wave data from an underlying buoy. These techniques promise to produce new methods for measuring waves and currents from stationary and moving platforms.