A derivative spectrum algorithm for determination of chlorophyll-a concentration in the Pearl River estuary

Abstract

Chlorophyll-a is the pigment presented in living plants or phytoplankton responsible for the photosynthesis, and it is a very important ecological and environmental parameter of waters, not only used for estimation of ocean primary productivity, but also for detection of red tides and for water quality. The chlorophyll-a concentration in coastal waters is generally overestimated from ocean color satellite data with common algorithm. In order to improve the remotely-sensed estimation of chlorophyll-a, many efforts have been made. In this study, six cruises for in situ data collection were conducted in lower reaches of the Pearl River and its estuary, the Lingdingyang, from 2003 to 2006. And the variables such as temperature, salinity, chlorophyll-a, total suspended matters (TSM), nutrients and gelbstoff absorption coefficient (Ag) were collected. The in situ remote sensing reflectance (Rrs) were measured from above waters with an ocean optics USB2000 spectrometer, which covers wavelength from 200 to 850 nm with spectral resolution of 0.38 nm. The original in situ Rrs data were processed to EO-1/hyperion bands (at resolution about 10 nm), and the derivative spectra with the different spectral resolutions were analyzed. The statistic analysis shows that the relative coefficient between derivative spectrum and chlorophyll-a is higher than that between original spectrum and chlorophyll-a. The band with highest relative coefficient to chlorophyll-a was employed for development of chlorophyll-a retrieval algorithm. A derivative spectrum algorithm was developed, and then applied to EO-1/hyperion data, which were acquired in December 16, 2006. The distribution image maps of chlorophyll-a concentration retrieved from EO-1/hyperion data were obtained. It shows that the derivative spectral method is an alternative approach for detection of water quality in coastal waters.