S K Singh
Articles written in Journal of Earth System Science
Volume 120 Issue 2 April 2011 pp 321-328
Snow is a highly reflecting object found naturally on the Earth and its albedo is highly influenced by the amount and type of contamination. In the present study, two major types of contaminants (soil and coal) have been used to understand their effects on snow reflectance in the Himalayan region. These contaminants were used in two categories quantitatively – addition in large quantity and addition in small quantity. Snow reflectance data were collected between 350 and 2500 nm spectral ranges and binned at 10 nm interval by averaging. The experiment was designed to gather the field information in controlled conditions, and radiometric observations were collected. First derivative, band absorption depth, asymmetry, percentage change in reflectance and albedo in optical region were selected to identify and discriminate the type of contamination. Band absorption depth has shown a subtle increasing pattern for soil contamination, however, it was significant for small amounts of coal contamination. The absorption peak asymmetry was not significant for soil contamination but showed a nature towards left asymmetry for coal. The width of absorption feature at 1025 nm was not significant for both the contaminations. The percentage change in reflectance was quite high for small amount of coal contamination rather than soil contamination, however, a shift of peak was observed in soil-contaminated snow which was not present in coal contamination. The albedo drops exponentially for coal contamination rather than soil contamination.
Volume 122 Issue 4 August 2013 pp 957-966
Indian National Satellite (INSAT) 3A was launched in the year 2003 with communication and remote sensing payloads. The later payloads contain very high resolution radiometer (VHRR) and charge coupled devices (CCD) camera. In this paper, post-launch calibration of INSAT 3A CCD is discussed. A cross radiometric calibration was carried out with well calibrated advanced wide field of view sensor (AWiFS) of Indian Remote Sensing Satellite (IRS P6). Three concurrent scenes of December, January and February were used in this study. Calibration was carried out under different land cover classes such as snow, vegetation, forest, water and cloud. Regression analysis suggests correlation coefficient of 0.95, 0.92 and 0.60 for Red, NIR and SWIR channels with slope values 1.839, 1.589 and 2.232, respectively. New calibration coefficients were used to estimate at-sensor radiance and reflectance in all the three channels. Dynamic range of reflectances was found to be improved by using new calibration coefficients. Normalized difference snow index and vegetation index (NDSI and NDVI) have shown an improvement with new coefficients and were found closer to represent