A Semi-analytical Approach to Understand Remote Sensing-based Backscattering Characteristics for Kerala Coast Using In Situ Observation
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A quasi-analytical algorithm (QAA)-based distribution and variability of particulate backscattering coefficient (bbp) was studied for Kerala coast, India. A total of 28 observations were made in the coastal stretch of about 410 km from Kasaragod to Ernakulam for up to 50 m depth. Optical data were collected using a hyperspectral underwater radiometer to evaluate the bbp, water-leaving radiance (Lw) and chlorophyll-a (Chl-a) concentration. We aimed to achieve three objectives, i.e. (1) QAA-based bbp calculation using underwater radiometer and its sensitivity to downwelling irradiance (Ed) and surface radiance (Es), (2) validation of the relationship between bbp and Chl-a concentration for inshore and offshore coastal waters and (3) the relationship of Lw with QAA-based bbp and in situ Chl-a. We observed that the range of bbp values varied between 0.07 and 0.002 m−1, with a maximum bbp value between 1200 and 1400 h for inshore waters. Ed and Es are independent variables and were placed at the denominator to calculate bbp, where Ed is found relatively more sensitive than Es. The correlation between bbp and Chl-a found growing with depth (< 20 m R2: 0.067, > 20 m R2: 0.487), due to the increasing complexity of coastal waters (Case II). While relating the Chl-a and bbp with Lw, showed a poor corleation with a low R2 value of 0.229 and 0.203, respectively, signifying the maximum scattering due to other suspended matters with less contribution from Chl-a pigment in highly turbid coastal waters.
KeywordsQuasi-analytical algorithm Hyperspectral radiometer Remote sensing reflectance Backscattering coefficient Chlorophyll-a
The authors are thankful to Project Director of ICMAM in facilitating the work.
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