Inland Lakes Algal Blooms Remote Sensing Monitoring And Evaluation

In recent years，China’s inland water eutrophication is becoming more and moreserious，result in algal blooms large-scale outbreak，the monitoring of algal bloomshas become an important task of water quality governance. The traditional monitoringby ships cruise on lakes can’t be comprehensive，timely to grasp the outbreak of alarge area algal blooms，while the remote sensing technology with a wide range ofarea，high temporal resolution，low cost of manpower and resources to become theprimary means of water blooms monitoring. Based on ground measure of the spectralcharacteristics of the algal blooms，and combine with the features of exist satellitedata as well as the actual monitoring，this paper selects NDVI index as the mainmethod to extract algal blooms，and uses the method of atmospheric correction，radiometric correction，region of interest extraction，etc. to improve the extractionaccuracy of algal blooms. This paper selects the uninterrupted data by remote sensingmonitoring to analysis the time and space evolution of Taihu water，and analyzes thefactors affecting algal bloom by measured water quality and meteorologicalparameters.The main research results and conclusions are as follows:(1) Based on spectral analysis of algal blooms，this paper selected NDVI as extractionmodel for HJ-CCD and MODIS data，and improve the extraction accuracy bymethods of observations and atmospheric correction，radiometric correction，geometric correction，the analysis of interest region，water threshold analysis，and hierarchical the extraction results.(2) Taihu Lake，for example，select remote sensing monitoring datas from2009to2012show that the distribution evolution of algal blooms in the inter-annual ofroughly the same，the algal blooms start at the north of western coast region，andpresents the diffusion rule that from north to south，west to east，and thefrequency，duration of algal blooms also follow this rule. It’s distribution area，outbreak frequency render the trend increased at the begin and then decreasedover time.(3) Water temperature is a major factor that affect algal density and the erupt of algalblooms，algal blooms begin to reproduce at15℃，inhibit reproduction whengreater than30℃，water temperature affect the overall situation of algal blooms.The wind direction mainly affects the distribution，wind velocity mainly affectsthe diffusion extent of algal blooms，it’s beneficial for expand at about2m/s andinhibit the diffusion above4m/s. Algal blooms was inhibited when water levelincreases，there is a great possibility outbreak of a large area of water among theprocess of water level reduction. Chlorophyll a and algal density is stronglyrelated，algal density and distributed of algal blooms is related，but the error isinfluenced by many factors. Total nitrogen and total phosphorus is the mainnutrient of algal blooms，there exist a response time difference between theconcentration change of TP TN and the multiplication of algal blooms. PH valuechanges by scale concentration of algal blooms，the secretions produced by the algal blooms change the inherent PH value of the water body.