Quantitative analysis of chlorophyll-a reflectance spectrum in red spectral region of water

Abstract

The chlorophyll-a concentration in waters is one of the main parameters of water color remote sensing in case II waters. There is a reflectance peak in red band region because of inherent optical properties. Based on the coefficients of absorption and backscattering of waters, colored dissolved organic matter (CDOM), tripton and chlorophyll-a, the reflectance of remote sensing was simulated according to the forward radiation transfer model without the consideration of fluorescence peak. The reflectance peak intensity and reflectance peak position at different wavelengths in red band region were analyzed with different chlorophyll-a concentration. There is a good linear relationship between the red reflectance peak intensity and chlorophyll-a concentration when the chlorophyll-a concentration is 1-50 microg x L(-1). But the linear relationship between the reflectance peak intensity and chlorophyll-a concentration will decrease with the increasing chlorophyll-a concentration. When chlorophyll-a concentration is up to 1 000 microg x L(-1), the logarithm relationship between the reflectance peak intensity and chlorophyll-a concentration is better than linear relationship. The wavelength position of reflectance peak in red band region will shift towards larger wave-length at logarithmic growth rate with increasing chlorophyll-a concentration, and the logarithm relationship will be more apparent with the inoreasing chlorophyll-a concentration. The same trend happens to the reflectance peak intensity and the wavelength position of peak in red region with different in-water constituents, such as CDOM, tripton and so on. Furthermore, according to the comparison with fluorescence peak, the authors also found that the reflectance peak intensity and the wavelength position of peak in red region are different from those of the fluorescence peak.