Research On Retrieval And Temporal Changes Of Chlorophyll Concentration In Hong Kong Sea

With the development of coastal areas in China,human activities increase and a large amount of sewage is discharged into the sea,which leads to the occurrence of red tide in offshore eutrophication,and Hong Kong sea area is also a high red tide area.Therefore,the monitoring of phytoplankton is urgent.The most representative factor is chlorophyll concentration.This paper uses Gao Si process regression(GPR)model and C2RCC model based on machine learning algorithm to retrieve chlorophyll concentration in Hong Kong sea area from 2017-2018 and verify the inversion accuracy by precision analysis.The spatial variation and quarterly difference of chlorophyll concentration in Hong Kong sea area in 2017-2018 were analyzed by inversion results.The findings are as follows:(1)The average correlation R~2between the 2017-2018 GPR model and the measured data is 0.68,and the average correlation R2 of the C2RCC model is 0.51,which the GPR model is better than that of the C2RCC model.(2)A GPR model is used to retrieve and analyze the monthly chlorophyll concentration in the surface,middle and bottom layers of Hong Kong in 2017-2018.According to the inversion results,it can be found that the highest value in two years appears in the surface sea area,The lowest values appear in the bottom waters,The spatial distribution characteristics of chlorophyll in Hong Kong sea area show obvious vertical decline from month to month.There were two obvious peaks in chlorophyll concentration during the year,Show a low-high-high-low trend.Average chlorophyll concentration in the surface was 8.7?g/L,in August 2017 Average chlorophyll concentration was 0.8?g/L.in October 2018 In the two years,the high chlorophyll concentration in Hong Kong sea area was concentrated in the sea area of the Aberdeen,The waters of Tolo Harbour and Chimen Strait and the Southern District,The main reason is that the water pollution is more frequent and the chlorophyll concentration is higher.(3)According to the GPR model,the seasonal difference of chlorophyll concentration in Hong Kong sea area can be obtained by inversion of spring,summer,autumn and winter in 2017-2018.The season of overall chlorophyll concentration change is about autumn>summer>spring>winter.In 2017-2018,the average chlorophyll concentration of the whole season showed a low-high-high-low trend,with obvious peak in summer and autumn,and low value in spring and autumn.The average chlorophyll concentration in the surface layer in autumn 2017 is higher than 7.2?g/L,and the lowest chlorophyll concentration is 1.4?g/L.in the middle and bottom of spring 2017 This phenomenon is mainly due to the higher temperature of the sea surface in summer and autumn,and is more suitable for the growth of phytoplankton,resulting in the increase of chlorophyll concentration.