Research On Inversion Algorithms Of Chlorophyll Concentration About Red Tides Monitoring In Bohai Sea

In this paper, an overview of the Bohai Sea and its red tide characteristics were described and analyzed. It showed that red tides had an increasing trend, especially in the21st century. Red tides mainly occurred between May and October. The variations of red tides in Bohai Sea were characterized by a large area, expanded distribution and increased dominant species.In this paper, chlorophyll inversion models were estabilished using SeaWiFS MODIS and TM with in-situ chlorophyll concentration in order to establish suitable inversion algorithm in red tide monitoring for the Bohai Sea. Then spatial and temporal distribution of chlorophyll concentration based on MODIS and SeaWiFS data were analyzed. Statistical methods were used for the analysis, including anomalies, running average, discrete-time power spectrum and so on.SeaWiFS1A data were used to to do the remote sensing reflectance ratio of443nm,490nm,510nm and555nm. The maximum R2is0.789and the average relative error was89.8%; TM data was used with1,2,3,4-band and for various combinations. The maximum R2was0.372and the average relative error was6.11%; MODIS1B of1～7bands through the atmospheric corrected reflectance data were used. The ratio of7-band with4-band plus5-band had the best correlation. The maximum R2was0.610. The r average relative error for modeling group and test group were47%and24%, respectively.Seasonal changes of chlorophyll concentration represented bimodal shape. The peaks were in early spring in March and the fall in September and the lowest in July. Annual variation was characterized by higher concentrations in the year of1998and2006. Spatial distribution showed concentration gradually descended from coastal waters to out of the Bohai Sea, and the lowest concentrations were in the Bohai Strait and near the mouth of the North yellow.Finally, the established inverse model with MODIS successed to retrieve3typical large area red tides occurred in the Bohai Sea from2004to2005. The retrieved results are good. However, the retrieved chlorophyll concentrations were lower than in-situ chlorophyll concentrations when using histogram minimum method for the atmospheric correction. In the future, the development of more appropriate atmospheric correction methods and high spatial resolution satellite data to establish inversion algorithms of chlorophyll concentration are very important in the Bohai Sea.