Aerosol Optical Depth Over Ocean From Ocean Color Monitor-3 Onboard the Earth Observation Satellite (EOS-06)

The continuance of satellite-based retrievals with series of space-borne sensors is essential to generate long-term climate quality data records. Indian Space Research Organization (ISRO) launched Ocean Color Monitor-3 (OCM-3), onboard the Earth Observation Satellite-06 (EOS-06, Oceansat-3), which is the third one in the series of OCM sensors. EOS-06/OCM-3 has potential for the retrieval of AOD at 555 nm ( $\tau _{555}$ ) over oceanic regions at pixel-level resolution of 366 m at nadir. Here, an algorithm for AOD retrieval based on lookup table (LUT) approach, employing radiative transfer (RT) computations to account for multiple scattering in the atmosphere, is presented. LUTs of top of the atmosphere (TOA) reflectance are generated with region and season specific aerosol models, based on the measurements of aerosol properties over the oceanic regions around India in premonsoon and winter seasons. Theoretically expected uncertainty in $\tau _{555}$ from OCM-3 ( $\tau _{\text {OCM3}}$ ) is estimated to be $\varepsilon _{\tau } = 0.1 \times \tau +0.02$ (correlation coefficient, $R \; = 0.95$ ). Validation of $\tau _{\text {OCM3}}$ with AERONET AOD shows a linear regression slope (m) 0.79, intercept (c) 0.02, and R $0.85. \; \tau _{\text {OCM3}}$ is in good agreement with MODIS AOD with m, c, and R values 0.996, 0.06, and 0.78, respectively, and thereby ensures continuity of climate quality AOD data for longer period. The retrieval of AOD from OCM-3 at a finer spatial resolution would significantly improve regional characterization of aerosol properties and assessment of aerosol climate impacts.