Airborne passive polarimetric measurements of sea surface anisotropy at 92 GHz

The potential for remote sensing of ocean wave direction using passive polarimetric microwave observations was investigated. A fixed-beam 91.65 GHz polarimetric radiometer was mounted on the NASA DC-8 aircraft during the Tropical Ocean Global Atmosphere/Coupled Ocean Atmosphere Response Experiment (TOGA/COARE January-February 1993). Several experiments were performed during which the DC-8 was flown in constant bank-angle turns at /spl sim/1.5 km altitude to obtain azimuthal scans of the sea surface at fixed observation angles. Data at 650 from nadir are consistent with previous findings using 19- and 37-GHz Special Sensor Microwave Imager (SSM/I) satellite observations and support the claim that a broadband emission mechanism is responsible for the azimuthal brightness signatures. Accordingly, a tilted-facet geometrical optics (GO) model of the surface was developed to investigate emission from deterministic and random striated surfaces. Laboratory measurements of polarimetric emission at 92 GHz from small-amplitude water-waves corroborate this model.<>