Polarimetric microwave brightness signatures of ocean wind directions

Abstract

'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.

Aquarius geophysical model function and combined active passive algorithm for ocean surface salinity and wind retrieval

“…The amplitudes of e 2v and e 2h are about the same although the sign of e 2h is negative. The characteristics of e p1 and e p2 are similar to those of higher-frequency (10-37 GHz) radiometer data [Yueh et al, 1999;Yueh et al, 2006;Yueh, 2008].…”

Wind direction over the ocean determined by an airborne, imaging, polarimetric radiometer system

“…Most experimental work has been performed employing a staring radiometer pointing toward the sea surface while the aircraft makes full 360 turns. Thus, the radiometric signatures as a function of azimuthal observation angle relative to the wind direction were investigated [1]- [4].…”

“…The incidence angle is 55 , and the frequency is 16 GHz. The curves are based on results from previous experiments [1]- [4]. The second Stokes parameter, , has a typical variation of 3 K around a mean value of 63 K. This mean value is dependent on frequency, wind speed, atmospheric attenuation, and other geophysical parameters.…”

Effects of air-sea interaction parameters on ocean surface microwave emission at 10 and 37 GHz

“…The effect of rotation of the polarization axes by an angle in the clockwise direction is a linear transformation as [4] (1) where , , , are the four modified Stokes parameters in brightness temperatures in the measured polarization basis, and , , , are the same parameters in the ideal polarization basis. Since the roll angle is small and is much smaller than or (aircraft measurements show that its value is less than 4 K peak-to-peak for the wind speeds encountered during FAIRS, e.g., [5]), the term was neglected to correct the first two modified Stokes parameters for roll angle variations.…”