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

Abstract

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 τ_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.

Acknowledgements

This work was supported under the Meteorology and Oceanography Programme (MOP) of the Indian Space Research Organisation (ISRO). Ms Nivedita Sanwlani and Dr Prakash Chauhan are thankful to Dr Ajai, Group Director, Marine and Planetary Sciences Group (MPSG), and Dr J. S. Parihar, Deputy Director, Earth Ocean Atmosphere and Planetary Sciences Applications Area (EPSA) of the Space Applications Centre (ISRO), Ahmedabad, for their valuable advice and encouragement.