Post-launch calibration of the INSAT-3A-CCD geostationary satellite sensor

Post-launch calibration was carried out for red and near infrared (NIR) bands of an Indian National Satellite System (INSAT)-3A-CCD camera over the Bay of Bengal (BOB) region. For this purpose, a coupled ocean-atmosphere radiative transfer (COART) model constrained by in situ measurements was used to simulate top-of-atmosphere (TOA) radiance for red and NIR bands. Comparisons were made between the simulated radiance and the charge-coupled device (CCD)-measured radiance. Analysis shows that for clear deep ocean pixels, the CCD camera overestimates TOA radiance in the NIR band by 74.8%, while it underestimates the radiance in the red band by 20.6% with respect to simulated radiances. Calibration factors were computed for the red and NIR bands of the CCD camera. Differences in simulated radiance and satellite-derived radiance were limited to 2.6% for the red band and up to 2.25% for the NIR band by applying these calibration factors. Validation of the calibrated radiance was done by performing a comparative analysis of aerosol optical depth (AOD) at 550 nm calculated from the calibrated INSAT-3A-CCD radiance, with in situ measured AOD (550 nm) and MODIS-derived AOD (550 nm). It was also found that the difference in uncalibrated radiance for the red band overestimated AOD (550 nm) by 155.65% when compared with in situ measurements, which was brought down to 1.48% after calibration. A comparison of INSAT-3A-CCD-estimated AOD (550 nm) was also done with MODIS-TERRA-derived tau(a) (550 nm). Spatial distribution of AOD after this calibration process matches well with spatial distribution of MODIS-derived AOD products for 550 nm. A good correlation was observed with R-2 = 0.94 with root mean square error (RMSE) of +/- 0.036 between the INSAT- and MODIS-derived AODs.