Will the aerosol derived from the OCM satellite sensor be representative of the aerosol over Goa?
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Most of the ocean color satellite sensors such as IRS-P4 OCM, SeaWiFS and MODIS are sun synchronous and have pass over the regions during noon. From our measurements of aerosol optical properties using five-channel sunphotometer over the coastal regions of Goa, India, diurnal variations of the aerosol optical properties are observed. The usual patterns observed are high values during morning, which gradually decrease in the evening. These diurnal variations are attributed to land-sea breeze. This raises the question, if the aerosol properties derived from the satellite are representative of the aerosol variation over the region. Our analysis of the data for the period 2000-2006 show that the average absolute percent deviation of the mean value during the day from the mean value during the noon are 7,7.4,10, and 10.5 in the spectral channels of 440, 500, 670 and 870 nm. The variation in the Angstrom exponent is found to be 8.87 %. Most of the variations are observed to be within 10%, which is within a tolerable limit considering the error in the instrument, measurement and satellite-derived values. Seasonal variations are also observed of the variations of the aerosol data at noon from those in the morning and evening. Variations of data in the morning and evening were found to be large during summer compared to winter and post-monsoon period. The diurnal variations were relatively lower in the channel at 870 nm compared to other channels. The diurnal variations of Angstrom exponent indicate the variations in the size of the aerosol particles.
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