Polarimetric microwave brightness signatures of ocean wind directions

‘1’hc smsitivitics of wind direction signals i)) ]Jassivc microwal’c brightness temperatures of sea surfaces to wind slwccl, incidcncc angle, polarization, and frequency are prwmted in this paper. ‘1’l)c cx]witncntal data were accluircd from ,a series of aircraft flights fro:n 1994 through 1996 by the Jet l’ropulsiorl Laboratory (JPL) using JP1i 19 and 37 G1lz polaritnetric radiometers (WINDRAI1). I’ouricr analysis of the data versus }vind dirwtiorl was carried out ancl the cocfficimts of Fourier scricx arc illustrated agaiust the wind speed at 45°, 55°, aud 65° incidmcc angles. Thm is a good agreement Mwccm the J1’L aimaft flight data and M’cntz’s SSIVI/1 geophysical mode] fuuction for the vertically polarized brightnms tcmpcraturcs, but Wmtz’s SSM/I wind direction model for horizontal polarization shows a significantly strollgcr upwind and clownwitld asymmetry than the aircraft flight data. Com~)ariso]l of the dual-frcqumcy WINI)RAIl data shows that, the wind direction signals arc similar at 19 and 37 GHz, although the 37 GIIz data have slightly strollgcr sigmds tllau the 19 GIIz data. in gmcral, tllc azimuthal variations of brightness tmn~m-aturcs irm-ease with increasing wind sped from low’ to lllOdC1atC willds, thml ]c’w] off and decrease at ]ligh wiuds. Tllc only mcq)tion is the t] mcasure]nmlt,s at 65° iucidcnce angle, which haw a st rongm than expected sigllal at lo}v winds. An cxponcmtial function was ~)roposcd to model the scnwitivitics of wind direction signals to wind S] MWCIS. The coefflcicllts of the em~)irical model are j)rovidcd ill this pa]mr and am useful for the simulation of ocean bright]lms tcm]maturcs ancl for the clcve.lopmmt of gmphysical retrieval algorithms.