Detection and monitoring of Trichodesmium blooms in the coastal waters off Saurashtra coast, India using IRS-P4 OCM data

Abstract

Trichodesmium blooms have been observed in the coastal waters off Saurashtra coast, Gujarat, India using Indian Remote Sensing satellite IRS-P4 Ocean Colour Monitor (OCM) data. Bloom-forming features were identified using false colour composites of channels 8, 6 and 5 (865, 670, 555 nm). Several bloom features of Trichodesmium like spiral eddies, stripes, slicks and parallel bands were detected in satellite images during 29 April to 7 May 2002. A strong backscattering signal was observed in the near-infrared band of OCM data, indicating the surface manifestation of Trichodesmium bloom. The chlorophyll images have been analyzed during the bloom period; overestimation of pigments has been observed and the bloom patches appear darker. Subramaniam’s protocol for Trichodesmium bloom study has been evaluated utilizing IRS-P4 OCM data for the waters off Saurashtra coast and appeared to be relevant in detection by ocean color remote sensing. The in situ information confirmed the presence of the bloom as coastal waters turned dark brown in color with an appearance of sawdust spray.