Blue Algae Extimation Based On MERIS Data In Taihu Lake

Taihu Lake is one of the five largest freshwater lakes in China's Yangtze River. Over the last decade, with the surrounding area of Taihu Lake to accelerate the pace of urbanization and population growth, water pollution, eutrophication is serious; there has been a very serious phenomenon of algal blooms. Remote sensing technology can be used to provide timely distribution of the entire lake algae very quickly.In order to obtain more accurate information on cyanobacteria, the semi-analytical model retrieved phycocyanin pigment concentration was established, using field measured data spectral data and the indoor water parameter data. And a remote sensing quantitative retrieval phycocyanin pigment concentration method was offered based on MERIS data. At the same time, retrieved chlorophyll a and phycocyanin pigment concentration using MERIS data, analyzed differences in the ratio of two different pigments and discussed the relationships between different pigments ratio and the algae bloom. The major achievements are as follow:1. Optical Properties of Taihu Lake and sensitive wave band of phycocyanin pigment.According to comprehensive analysis of relationship between phycocyanin pigment and remote sensing reflectance, remote sensing reflectance and phycocyanin pigment is in negative correlation at 400～700nm range and in positive correlation at 700～900nm range. Phycocyanin pigment and remote sensing reflectance has some negative correlation at 620m, but the relationship is not very obvious.According to analysis of absorption coefficient of water constituents and ratio of algae pigment and non pigment particles, phycocyanin pigment has strong absorption at 620nm. But because its absolute absorption ability is not stronger and other pigments also have absorption ability at 620nm, the correlation is not very noticeable. Therefore, we should take consideration of the influence of other pigments when the model build.2. The establishment of the semi-analytical model retrieved phycocyanin pigment concentration.Establish the semi-analytical model retrieved phycocyanin pigment concentration with measured data; when compare the accuracy of the results among the newly established model and the other three models, the new modle performed better than the others. In addition, a semi-analytical model retrieved phycocyanin pigment concentration was established based on MERIS data, from the field measured data model. 3. Retrieved the water pigment which contains chlorophyll-a and phycocyanin pigment concentration of the Taihu Lake based on MERIS data and the research about the pigment relationships.Phycocyanin pigment concentration and chlorophyll-a were retrieved using MERIS data.Two issues were discussed when the retrieved results of chlorophyll-a for remote sensing was testing:Observation point scale is inconsistent with the measured point and the image is consistent with synchronization in transit. And the results are:Variations of the water quality parameters is limited in a 300 X 300 meter pixel. Meanwhile, Relationship between the field measured data time of every point and transit time of the satellite and relative error should be considered when verify the accuracy of the retrieved water quality parameters. In other words, the bigger the interval is,the higher the accuracy of the retrieved water quality parameters is.Because all algae has chlorophyll-a pigment, only Cyanophytes has phycocyanin pigment, the radio of PC and chla can express relative biomass of Cyanophytes. At the same time, algae outbreak of algal and PC/chla has significant relationship. Sometimes, though chlorophyll-a pigment and phycocyanin pigment concentration were not very high, but PC/chla was very high in the waters of some areas. The areas of the lake has more dangerous algal bloom.There is a great possibility that algal bloom will break out in this kind of lake areas.