Possible Near-II? Channels for Remote Sensing Precipitable Water Vapor from Geostationat-y Satellite Platforms

Remote wssing of tropospheric water vapor profiles from current geostaticmary writher satellites are made using a few broadband infrared (IR) channels in the 6-13-pn~ region. Uncerminties greater than 21N0 exist in derived water vapor values just above the surface from the IR emission measurements. [n this paper, we propose three near-[R channels. one within the O.94-jMr1 water vapor band absorption region. and the other two in nearby atmospheric windows. for remote sensing of precipitable Water Vapor over land areas. excluding lakes and rivers, during daytime from future geoslationary satellite platforms. The physical principles are as follows. The reflectance of most surface targets vanes approximately linearly with wavelength near I pm. The solar radiation on the sun-surface-smsor ray path is attenuated by atmospheric water vapor. The ratio of the radiance from the absorption channel with the radiances from the two window channels removes the surface reflectance etTec[s and yields approximately the mean atmospheric water vapor w~nsmiltance or the absorption channel. The integrated waler vapa amount from ground to space can be obtained with a precision of kttter than 5% from the mean transmittance. Because surface retlec[ances vary slowly with time. Lempcml variation ofprecipitable wa[er vapor c~n be determined reliably. tiigh SPJLK II resoluti cm. prcc!pl table water “,opor images are derived t’rom spectral dtita collected by [he A(rhorne Visible-lnl’rared lrnag!ng Sp+xlrometcr. wh)ch memures solar radiation retlected by the surface In the 1)4-2 .5-pn] rcgmn In 10-nn] channels and h~s a ground lns[~ntaneous tield ol’view of N m from Its platform on ~n ER-2 aircraft at 20 km. 1 he proposed neitr-l R rctlecmnce technique would complement the [R emission tcchrslques for remote sensing of wa[er vofmr prolilcs from geosta[io nary wtclll[e platforms, especmlly In the boundary layer where mosl of the water vapor IS Ioca[ed.