Comparative Study on the Optical Properties of Inland Lakes using IOP and AOP Profiler: A Hyperspectral Remote Sensing and QAA Approach

The inherent optical properties (IOP) and apparent optical properties (AOP) were studied using IOP (AC-S sensor-Seabird Scientific Instrument) and AOP profiler (Satlantic free falling optical profiler) in two different lakes from Tamil Nadu and Kerala. The optically active substances, such as total suspended matter (TSM), Secchi disc depth (SDD), chlorophyll-a (chl-a), the absorption coefficient of chromophoric dissolved organic matter (CDOM), non-algal particulate matter, and phytoplankton, were analyzed in our research laboratory. The quasi-analytical algorithm (QAA) (inversion model)-derived absorption coefficient from AOP profiler measured reflectance was compared with the absorption measured from the AC-S sensor instrument, and the shifting of reference wavelength from 670 to 710 nm was done on the QAA steps for attaining the accuracy of the retrieved dataset. A scatter matrix was developed between the optically active constituents (OACs) to study the association between total absorption coefficient, CDOM, phytoplankton, detritus, TSM, and turbidity. The result shows that the absorption coefficient (1.757-3.649 m(-1)) is high in Vembanad Lake where the chl-a concentration is high (168.37 & mu;g/L). In Kolavai Lake, it is found that chl-a concentration is less (53.96 & mu;g/L) and the absorption coefficient (0.947-2.552 m(-1)). This is high due to its ecological conditions (decaying of macrophytes, houseboat effluent discharges, domestic wastes, etc., causing aquatic ecological imbalances that stimulate the eutrophication level and increase the absorption coefficient at Vembanad Lake). The backscattering coefficient b(bp) decreased with increasing wavelength and had a positive relationship with chl-a in Vembanad Lake and a negative correlation with TSM in Kolavai Lake.