Semi-analytic algorithm for retrieving pigment concentrations in the red tides areas of the east china sea

Red tides cause the serious problems in the East China Sea (ECS). Environmental and economic impacts of red tides have increased in the recent years. Thus, considerable efforts have been spent on red tides research. Ocean color remote sensing is one of the useful techniques, and the research of retrieving the concentrations of the water components has been applied in the areas. Because of the complex of the water properties, the pigment concentrations are hard to retrieve. Some algorithms, including of experiment algorithms and semi-analytic algorithms, have been developed or used to retrieve pigment concentrations. However, no suitable algorithm can be used directly to retrieve pigment concentrations in the red tides areas of the ECS now. In this paper we present a semi-analytic algorithm to retrieve the chlorophyll-a concentrations in the red tides areas of the ECS. Based on the measurements of the red-tide cruises in the ECS during 2002-2005, we have developed a spectral simulation model. Then the semi-analytic algorithm with MODIS wavelengths has been developed based on the simulation data. Different bands combinations have been trained to make the algorithm the best performance. The in situ measurements have been applied to validate the algorithm. When the concentrations of the total suspended matters are lower than 7 gm-3, the relative mean error of the algorithm is 38.34% and the correlative coefficient between the retrieved chlorophyll-a concentrations and in situ data is 0.8. The results show that the retrieved data agree well with the in situ ones. The algorithm can be used to retrieve the chlorophyll-a concentrations in the red tides areas of the ECS.