Sea truth validation of sea WiFS ocean colour sensor in the coastal waters of the eastern Arabian Sea
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In this paper we report bio-optical measurements made during an ocean colour validation cruise SK 149C in November 1999 of the research vessel Sagar Kanya in the coastal waters of the Eastern Arabian Sea. The chlorophyll concentration in these waters was in the range 0.2 to 4 mg/m3. Although the matchups between in situ and satellite data from SeaWifs were sparse, it indicates that direct application of the standard SeaWifs algorithm – the OC2-V4 algorithm – in the coastal waters of the Arabian Sea will underestimate chlorophyll by up to 30%. Comparison of our in situ normalized water-leaving radiance [Lwn] and chlorophyll measurements at sea with that derived from the SeaWifs colour sensor shows that SeaWifs overestimates both Lwn and chlorophyll. Various authors have earlier reported under and over estimation of SeaWifs water-leaving radiances, speculated as arising from variable errors when correcting atmospheric effects in coastal regions. These errors are produced most probably by absorbing aerosols and also from increases in water-leaving radiance caused by enhanced particle backscatter effects from sea water constituents other than chlorophyll. Further studies are required to resolve the problem of validating satellite sensors in coastal waters.
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