Application of Spectral Signatures and Colour Ratios to Estimate Chlorophyll in Singaporeʹs Coastal Waters

In this paper, a study of the spectral signatures of coastal surface waters in the Johor and Singapore Straits and the application of colour ratios to estimate chlorophyll is presented. In general, the spectral signatures of coastal waters in Singapore could be represented by two profiles. The first was characterized by a high major reflectance peak at 577 nm which decreased toward the blue and near infra-red (NIR) bands. Such a profile was obtained when chlorophyll levels were low (less than 5 g l 1). The second profile, which was obtained during periods of high chlorophyll (greater than 10 g l 1), was characterized by an overall lower reflectance over the visible spectrum, with a distinct absorption trough at 672 nm and reflectance peak at 695 nm. In general, suspended solids (ranging from about 4 to 100 mg l 1) increased reflectance in the green wavebands relative to the red/NIR region. The effect of dissolved organic carbon on the reflectance spectra was generally considered small due to its low concentration (<3 mg l 1). Blue-Green and Red-Near Infrared colour ratios were correlated with chlorophyll a, with the latter generally producing better correlations (R2=0·63).