Removing Path-Scattered Radiance from Over-Ocean Spectrometer Images for Water Vapor Estimation

Analysis and interpretation of high-altitude, optical observations of the marine environment requires compensation for atmospheric effects. However, some of these effects, such as water vapor absorption, are difficult to compute due to the significant atmospheric scattering relative to surface reflection and upwelling radiance. We separate atmospheric path-scattered radiation from surface reflectance using ocean wave-induced spatial modulations in the at-sensor radiance image. A new spectrum is constructed from the amplitude of the spatial modulations found in each wavelength band. Water vapor absorption is computed using the modulated spectra employing standard techniques applicable to bright targets (such as are incorporated in the atmospheric removal code ATREM). The algorithm can be extended to retrieve water vapor per pixel by removing an effective atmospheric reflectivity from the radiance field. This effective reflectivity is computed from differences in absorption features between the modulated and original spectra. These techniques are demonstrated using Airborne Visible/Infrared Imaging Spectrometer hyperspectral data acquired over the Santa Barbara Channel.