Improved estimates of bio-optical parameters in optically complex water using hyperspectral remote sensing data

In this study, bio-optical parameters were derived from hyperspectral data of optically complex waters using spectrum matching technique (SMT). Models for inherent optical properties (IOPs) of the water column were tuned using in-situ dataset from the study area (i.e., Chilika lagoon). Constructed IOPs were used to simulate remote sensing reflectance (R-rs) spectra at 60 wavelengths (equally spaced between 400 and 700 nm) using radiative transfer solution provided by Hydrolight-Ecolight software (HE53). Results of the simulation were stored as a R-rs - IOP look up table (LUT). To check the accuracy, in-situ measured R-rs were compared with those from the LUT. Retrieved values of two bio-optical parameters i.e., chlorophyll-a concentration (Chl-a) and coloured dissolved organic matter (CDOM)+Detritus absorption coefficient at 440 nm (a(dg)(440)) were compared with corresponding in-situ measurements to get good statistical match. Coefficient of determination (R-2) and root mean squared error (RMSE) were 0.80 and 2.66 mg m(-3) respectively for Chl-a, whereas 0.77 and 0.23 m(-1) respectively for a(dg)(440). These parameters were also retrieved using two commonly used semi-analytical inversion algorithms (SAA)- (a) Linear matrix inversion (LMI) and (b) Garver-Siegal Maritorena (GSM). Both the SAA showed poor performance. R-2 for Chl-a from GSM and LMI were 0.13 and 0.41, respectively, with RMSE of 6.85 mg m 3 and 4.82 mg m(-3) respectively. For (dg)(440), the value of R-2 from GSM and LMI were 0.87 and 0.71, respectively, but with a high RMSE of 0.91 m(-1) and 0.81 m(-1) respectively. SMT was applied to airborne hyperspectral AVIRIS-NG (Airborne Visible/Infrared Imaging Spectrometer Next Generation) dataset of Chilika lake to derive pixel-wise chlorophyll-a concentration and the magnitude of CDOM+Detritus absorption coefficient at 440 nm (adgo440THORN). Spatial variability of these parameters in its different domains (i.e. Northern-, Centraland Southern-region of the lake) have been addressed.