Empirical anisotropic spectral reflectance model for snow derived from

Modeling the anisotropic reflectance of snow will be important for various applications, like climatology, meteorology and water management. Accurate climatic and meteorological modeling of energy balance needs to take the anisotropic effect into account. This is also the case for accurate snow-cover mapping for water management. This paper describes the development of an empirical model for the anisotropic spectral reflectance of snow based on airborne DAIS-7915 spectrometer data covering the spectral range 0.4-12.6 micrometer. The data set used is from the Jotunheimen mountain area in Norway. Flight lines were in the solar plane and orthogonal to this, and a swath angle range of ±26 degrees was obtained. Combined with the effect of terrain slopes, an actual terrain incidence angle range of ±40 degrees was obtained. An accurate terrain model was derived from digital aerial photographs. Areas without snow were masked out based on another infrared high-resolution digital aerial orthophoto. Field measurements confirmed homogeneous conditions allowing a large area of data to be used. Field measurements were also applied for calibration. The raw angle-to-reflectance data were smoothed and represented in a 3D data storage model for further applications. The observation angles varied between –45o and 36o and the solar zenith angle varied between 24o and 55o. A hot-spot region representing forward scattering showed about 8% increase in radiance values. This anisotropy remained constant up to wavelengths of about 1700 nm. No anisotropic effects were detectable beyond this wavelength.