Research Developing Trend Of Chlorophyll-a Concentration In Chaohu Lake Based On Remote Sensing

The concentration of chlorophyll-a is one of the most important indexes evaluating eutrophication in lakes, the important contents of water quality monitoring of lakes. Therefore the investigation of chlorophyll-a concentration makes a significant contribution to understand eutrophication degree and its developing trend, it is of significance to control harm of the algae bloom. However, the conventional method is to measure the chlorophyll-a from point to point, with great expense in time and money, it only could obtain water quality parameters of partial representative area. These water quality parameters can't reflect distribution of chlorophyll-a in large lakes. This could be solved using remote sensing technology.In this paper, Multi-temporal images of TM/ETM+ were carried out atmospheric modification by the method of many dark pixels. The model of (B2+B4-B3)/ln(B3) was chosen finally by analysing water spectrum of inland lake and different combination of bands and different fitting forms. The images of TM/ETM+ were processed by the model of (B2+B4-B3)/ln(B3) and then the concentration of chlorophyll-a was calculated. Multi-temporal images of TM/ETM+ were classified into 5 scales and then obtain the distribution of chlorophyll-a concentration images.Through analyses on these images, the area of high chlorophyll-a concentration that over 200μg/L was mainly distributed around the mouth of NaiFeiHe river.The water quality of NanFeiHe River contributed more to algae bloom in Chaohu Lake. The area of high concentration had tendency of expanding to the east of Chaohu Lake. The change of temperature had greatly impact on the reproduction of algae. The algae bloom of Chaohu Lake represented regularity with change of seasons. The concentration of chlorophyll-a had changed from middle-low concentration mainly at 1995/8/1 to middle-high concentration mainly at 2006/7/30. Intensity and range of algae bloom in Chaohu Lake all present raise situation. Though many kinds of treatment measures had been taken, the trend of algae bloom unchanged fundamentally and the degree of eutrophication would be still aggravated.