Estimation of spectral reflectance of snow from IRS-1D LISS-III sensor over the Himalayan terrain |
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| Authors: | J Srinivasulu A V Kulkarni |
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| Institution: | (1) Marine and Water Resources Group, Space Applications Centre, 380 015 Ahmedabad, India |
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| Abstract: | The sensor onboard the satellite views the earth as a plain surface and consequently the satelliteobtained spectral radiances
cannot represent true values over a mountainous terrain. The relative 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 variations in its spectral reflectances. Since, the terrain geometry also modifies
the amount of reflected radiation from a rugged surface, one has to correct the estimated spectral reflectances for terrain
topography so as to use them in deriving the snowpack characteristics accurately. Also, the amounts of melt runoff originating
from glaciers having different 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 satellitebased radiance measurements
and includes the effect 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 differences 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. |
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| Keywords: | Snow reflectance IRS Himalaya |
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