8 December 2006 Estimation of aerosol optical thickness over land using dual angle panchromatic data
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Estimation of atmospheric aerosols by remote sensing is very important because aerosols cool/warm the Earth atmosphere system through scattering/absorption of solar radiation. The information on aerosol optical thickness (AOT) is also essential in atmospheric correction of satellite imagery. Due to non-uniformity and extreme reflectivity of land targets, it is challenging to monitor aerosols over land-surfaces. This paper reports a new approach of estimating AOT over land using dual viewing angle observations (FORE: 26 degree and AFT: -5 degree) in panchromatic channel (0.50- 0.85μm) of Cartosat-1 satellite. Differential responses of targets observed in two atmospheric path lengths through Fore and Aft observations of Cartosat-1 were analyzed using atmospheric radiative transfer model (6S-code). A number of forward simulations over dark to bright targets (having 1-70% reflectivity) were carried out to derive top-of-atmosphere (TOA) reflectance for various AOT conditions to arrive at a particular reflectance condition called- cross over reflectance (ρco: a reflectance value for which the difference between TOAAft and TOAFore equals zero). The shift in position of ρco for dual look angle was modeled as a function of AOT. Using this method, AOT was estimated for two sites representing clear and turbid atmosphere conditions. A cross over reflectance of 11 percent and 13 percent was observed for clear and turbid atmospheres, respectively. Corresponding modeled AOT estimates were 0.32 and 0.78, respectively. Validation of these estimates with the MODIS AOT showed good agreement with 0.26 in clear and 0.68 in turbid atmosphere case. The present approach enables to retrieve single AOT value for a scene and for known aerosol meteorology. Initial results are encouraging, however further analyses are in progress to verify it in different atmospheric conditions.
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Mehul R. Pandya, Mehul R. Pandya, } "Estimation of aerosol optical thickness over land using dual angle panchromatic data", Proc. SPIE 6408, Remote Sensing of the Atmosphere and Clouds, 64080X (8 December 2006); doi: 10.1117/12.693948; https://doi.org/10.1117/12.693948

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