Empirical relationships for remote sensing reflectance and Noctiluca scintillans cell density in the northeastern Arabian Sea

Abstract

A dinoflagellate under the ambit of Harmful Algal Blooms (HAB), the bioluminescent Noctiluca scintillans (NS), has been infesting the northern Arabian Sea increasingly over the last few decades during late winter. Their occurrence is found to be due to seasonal oscillations in the coastal currents. The physical and biogeochemical parameters associated with the seasonal blooms are reasonably well known. But accurate quantitative estimation capability using remote sensing sensors over the extensive oceanic regime is still lacking. This is especially due to a lack of information on bio-optical properties associated with cell density measurements. We attempted to show that remote sensing reflectance and chl-a show significant relationship e.g., R_rs(531)/R_rs(510) = 0.8261 + 6.06 × 10^-6NS + 0.02323chl-a (N = 19, R²_adj = 0.99, p = 2.5 × 10^-17, RMSE = 0.1083) which is applicable over diverse areas of the northeastern Arabian Sea e.g., coastal, shelf and offshore regions. The model is supported by a second dataset with an RMSE of 0.022893 (N = 8) for the R_rs(531)/R_rs(510) ratio. The NS cell densities were derived from the Rrs(510)/Rrs(531) band ratio within reasonable error and accuracy limits. Including sensor capability at 510 nm is suggested in future satellite launches.

Keywords: Bioluminescence; CDOM; Cell density; Chlorophyll-a; Dinoflagellate; Harmful algal blooms; TSM.