| > 20 | ||
| 16 ~ 20 | ||
| 12 ~ 16 | ||
| 8 ~ 12 | ||
| 4 ~ 8 | ||
| 0 ~ 4 | ||
| 0 |
Poyang Lake is the largest freshwater lake in China, and it plays an important role in flood control regulation and storage and biodiversity protection. Chlorophyll-a concentration level can reflect the status of water primary productivity, and it is also an important indicator of evaluating the eutrophication degree. The knowledge service production process is as follows: First of all, water body spectral information of Poyang Lake was measured in the field, and the spectral index was constructed based on the water spectral characteristics analysis; Then, based on the least squares method and combined with measured chlorophyll-a concentrations data, sensitive band interval was calculated by regression analysis; MODIS data was used to build chlorophyll-a concentration estimation models of Poyang Lake by semi-empirical method and the accuracy of the results was verified; Finally, chlorophyll-a concentration distribution data of Poyang Lake in January, April, July and October from 2009 to 2012 was inversed using these models. Data analysis show that: chlorophyll-a concentration in Poyang Lake had increased slowly from 2009 to 2012; It had a lowest concentration of each year from December to February, then rapidly rose to peak from March to July and fell down from August to November; In terms of spatial distribution, the high value area of chlorophyll-a concentration were located in the coastal waters, five rivers estuary water area, and the higher the concentration value was, the more significantly the spatial characteristics changed. The temporal and spatial change characteristic of chlorophyll-a concentration in Poyang Lake is the results of the lake nutritional condition, water temperature, water level changes, storms and human activities affecting together. Its temporal variation is mainly affected by natural factors such as changes in water area and so on, while the differences in spatial distribution is mainly influenced by the surrounding human shipping, sand mining and agricultural activities.
