Inversion And Distribution Characteristics Of Red Tide In The Bohai Sea

Since 2000,red tides have been reported in the Bohai Sea every year,which often made coastal waters of the Bohai Sea suffering from red tides.Satellite remote sensing technology and the ocean color observation satellite images have been successfully used to identify and observe the initiation,evolution,and dissipation of red tide.However,due to different water bodies,remote sensing data and modeling methods,a specific model of red tide inversion should be established for the water characteristics of the Bohai Sea.The world's first Geostationary Ocean Color Imager(GOCI)has a distinct advantage in monitoring the distribution and short-term movement of red tides in the Bohai Sea.Therefore,this paper used GOCI remote sensing data to establish a red tide inversion model based on an improved red tide index,and proved the validity of the red tide in the turbid waters.On May 15,26 and 28 of 2014,eight RI images showed the change of increase first and then decrease in the red tide area.Using the RI threshold of 3.8,4 or 4.2,although the area of red tide changed,the relative changes in one day remained consistent.The chlorophyll concentration in the red tide region reached a maximum at 11:30 on May 15,26 and 30,but the red tide is not positively proportional to the chlorophyll concentration.Therefore,GOCI can effectively carry out the short-term and long-term monitoring of red tides in the Bohai Sea.In this paper,the correlation analysis between MODIS spectral reflectivity data and measured concentration of chlorophyll a in the Bohai Sea was carried out.The expression(B10-B8)/(B13-B8)was chosen as the indicator of red tide inversion in Bohai Sea,the correlation coefficient reached 0.7815,showing significant correlation results.The study found that the variability of the maximum occurrence area of red tides during the period from 2000 to 2015 was obvious,with large areas of red tides and small areas of red tides appearing at intervals.The occurrence period of red tide is from April to November,and the peak season of red tide is from May to July.The maximum value of red tide coverage in the Bohai Sea mostly occurs from mid-June to early July.The main areas of red tide in the Bohai Sea are the offshore waters of the Bohai Bay,the waters near Qinhuangdao in the western part of Liaodong Bay,the waters near Yingkou Bayuquan.and the offshore waters of the Huanghekou of Laizhou Bay,and most of them occur in coastal waters.Among them.the occurrence frequency of red tides in the waters around Qinhuangdao has been increasing year by year since 2000.From 2009,the large-scale brown tide of Aureococcus anophagefferens has been occurring every year in the sea near Qinhuangdao.which may be closely related to local aquaculture activities.In the late spring and early summer,the concentration of dissolved inorganic nutrients in the sea near Qinhuangdao,the increase of organic carbon and nitrogen concentration,and the suitable seawater temperature may be the important reason for the annual outbreak of brown tide in the sea area.The large-scale outbreak of red tides in the Bohai Sea since 2000 has been mainly caused by the poor water exchange caused by its semi-closed geographic shape and the input of large amounts of nutrients from coastal runoff.River input is the major source of terrigenous pollution into the sea.