Bio-Optical Characterization of Chilika Lagoon Using Multispectral Remote Sensing Data

Chilika Lake is an optically complex water body experiencing circulations linked to the tidal influx from Bay of Bengal. These circulations causes seasonal variations in biophysical and chemical parameters of the lake, such as water nutrients, salinity and chlorophyll-a (Chl-a). In this study, bio-optical parameters (Chl-a concentration, absorption by colored dissolved organic matter detritus and backscattering by suspended particles) of Chilika Lake were estimated using multi-spectral remote sensing data of Oceansat-2 Ocean Color Monitor (OCM-2, spatial resolution ∼ 360 m) and Landsat-8 Operational Land Imager (OLI, spatial resolution ∼ 30 m) sensors. Spectral matching technique was implemented on the satellite derived remote sensing reflectance spectra ( R_rs(λ ) ) to estimate the bio-optical parameters. Both OLI and OCM-2 revealed that the southern and central portion of Chilika has a relatively higher phytoplankton productivity (8 mg m^-3 ≤ Chl-a ≤ 15 mg m^-3 ) when compared to the northern sector. Also, retrieval from both the satellites could capture the presence of a high sediment load in the northern sector. Application of spectral matching technique requires accurate estimation of R_rs(λ ) from a satellite image. For this purpose, atmospheric corrections were implemented on both OLI and OCM-2 level-1b data. Processing of OLI data was done using SWIR (short wave infrared) atmospheric correction algorithm with the help of ACOLITE software. For OCM-2, due to the absence of SWIR bands, we used the standard atmospheric correction algorithm with certain modifications to obtain accurate results over the turbid waters of Chilika Lake. R_rs from OCM-2 were compared with in situ measured reflectance. Both the shape and magnitude of the spectra compared well, with relative errors ranging from 8.75 to 32.78