Improved regional algorithm to retrieve total suspended particulate matter using IRS-P4 ocean colour monitor data

Abstract

Data from seven validation campaigns in the coastal waters of the Bay of Bengal (BOB) were used to develop a regional SPM (suspended particulate matter) algorithm. The in situ data sets for this algorithm are obtained from 86 stations with optical and 68 stations with total SPM measurements encompassing SPM concentrations between 10 and 189 mg l⁻¹, where most of the observations are in shallow (case 2, average depth ~45 m) waters and a limited number of samples in open case 1 waters. From simple statistical analyses we found a close relationship between SPM concentration and diffuse attenuation coefficient at 555 nm (K555) in the BOB coastal waters. The linear regression to the fit has a coefficient of determination (r²) 0.96 with a standard error of estimates (σ)12.5 mg l⁻¹ for the above SPM range. The algorithm relating K555 to [L_wn443/L_wn670] has been evaluated through a regression analysis of radiometric profiles in the BOB. However, the new SPM algorithm overestimates in case 1 waters (SPM range 0.05–25.0 mg l⁻¹), where a spectral reflectance ratio algorithm (Tassan 1994 Appl. Opt. 33 2369–78) appears to produce better results. An integration of both the approaches performs better in generating the routine IRS-P4 OCM (ocean colour monitor) SPM mapped product.