LAUSR

The decoupling of aerosol signals from the at-sensor reflectance measured through a space-borne sensor is a complex task due to the involved coupling mechanism of the interaction of light with the Earth's surface and the atmosphere. Specifically, the retrieval becomes more challenging over the land surface due to appreciable reflectance from the target. This paper presents a simplistic physics-based approach to retrieve Aerosol Optical Depth (AOD) (at a spatial resolution of 0.01°) over the land surface from the top-of-atmosphere (TOA) signals measured from an Indian space-borne sensor, Ocean Color Monitor-2 (onboard OCEANSAT-2 satellite). The estimated AOD from OCM-2 has been compared with that from Moderate Resolution Spectroradiometer (MODIS) onboard AQUA satellite (Collection 6.1 Deep Blue/Dark Target product). The comparison is illustrated for two different conditions prevalent over the Indian region, i.e., smoke-dominated (post-monsoonal) and dust-laden (pre-monsoonal) periods. A case study is also illustrated for the pre- and post-COVID-19 lockdown time period for two different zones of the Indian region. The validation (comparison) of OCM-2 AOD is performed with respect to the data from AERONET stations (MODIS), and we found a correlation coefficient (R2) of 0.84 (0.83) with root mean square error (RMSE) of 0.14 (0.20). Also, ∼87% (70%) of the retrieved OCM-2 (MODIS) AOD values were observed within the expected error (EE) envelope. The sensitivity of the retrieval algorithm with respect to the input parameters is also presented.