A Semianalytical Approach to the Calibration of AVIRIS Data to Reflectance over Water: Application in a Temperate Estuary

Calibration of at-sensor radiance to reflectance is a critical step for the use of remotely sensed hyperspectral data of water to determine the concentrations of optically active components. Because water has such a low reflectance, sources of radiance other than the water-leaving radiance contribute significantly to the at-sensor radiance and vary with wavelength and spatially. While radiative transfer models have improved significantly, there are still large uncertainties in prescribing the spatial and spectral properties of aerosol scattering. In addition, errors in the sensor calibration of radiance can lead to additional uncertainty. An atmospheric correction method based entirely on scene information, but not in situ data, is described. This approach accounts for nonuniform aerosol scattering, glint from the water surface, and reflected skylight. Normalization by an estimate of the direct solar irradiance reaching the surface, also derived from scene information, then provides an estimate of reflectance. This method is applied to AVIRIS data acquired over a temperate estuary. The resultant reflectance estimates are shown to be consistent with field observations. While the method is empirical, it is based on physical principles that allow it to be applied under a wide range of conditions.