Estimation of spectral reflectance of snow from IRS-1D LISS-III sensor over the Himalayan terrain

The sensor onboard the satellite views the earth as a plain surface and consequently the satellite-obtained spectral radiances cannot represent true values over a mountainous terrain. The rela-tive magnitudes of terrain slope and its aspect with respect to the sun’s position will determine the amount of direct solar radiation incident on an undulating surface. Estimation of spectral reflectance from satellite data forms an important component in many of the snow and glacier studies. The spectral reflectance of snow is influenced by its various parameters. The changes in snowpack characteristics as a result of various metamorphic processes, with age, can cause varia-tions in its spectral reflectances. Since, the terrain geometry also modies the amount of reflected radiation from a rugged surface, one has to correct the estimated spectral reflectances for ter-rain topography so as to use them in deriving the snowpack characteristics accurately. Also, the amounts of melt runo originating from glaciers having dierent slopes and orientations will not be the same. Considering these aspects, a model has been developed to estimate the terrain corrected spectral reflectances over the Himalayan terrain using the Linear Imaging Self Scanner-III data of the Indian Remote Sensing Satellite. The model computes spectral reflectances from satellite-based radiance measurements and includes the eect of the terrain topography on the incident solar radiation. The terrain slope and its aspect are generated from the digital elevation model of the region. The analysis carried out over the Beas Basin, Himachal Pradesh, India, indicated a variation of 22 % in the amount of incident solar radiation for an increase of 10 in terrain slope. Further, the terrain with south-east aspect received maximum amount of solar radiation. The large dierences observed between the uncorrected and terrain corrected reflectances in the shortwave infrared band (B5), which is not saturated over the snow covered region, suggest that the terrain slope and its aspect cannot be neglected in estimating the accurate spectral reflectances over the Himalayan terrain. 1