| The first ocean color satellite of China(HY-1C)was launched on September7,2018,equipped with several optical sensors,including the Chinese ocean color and temperature scanner(COCTS),Coastal Zone Imager(CZI),and ultraviolet imager.These instruments were used in ocean and coastal zone environment monitoring in June2019.Tht optical remote sensing of oil spills is a key research direction in marine environmental monitoring.Significant progress has been made in recent years,demonstrating its ability to detect,classify,and estimate the volumes of various oil spills.In this paper,the marine oil spill incident near Dongsha Island in the South China Sea in 2019 was used as a case study,the ability of HY-1C to detect oil spills and the uncertainty in the signal are evaluated systematically.And then,for CZI data,sunglint reflectance difference between spilled oils and oil-free seawater has been considered,the method for oil spills extraction was studied;Finally,the method for oil spills extraction was tested on many CZI data over different rigions.The main research contents are as follows:(1)According to the oil spill incident near Dongsha Island in 2019,both HY-1C satellite data(COCTS and CZI)and other data(VIIRS and MODIS Terra&Aqua)were obtained,they were compared with each other on the ability of oil spills detection,and the performance of COCTS and CZI for oil spills identification was evaluated.(2)The near infrared band of CZI(825nm)was the optimal band for detection of spilled oils.Based on the difference of sunglint reflectance and features of oil-free seawater,a method is designed to realize extraction of oil spills under different sea environment and different sunglint condition.(3)The CZI data covering different oil spill areas were collected to test the universality and accuracy of the method for oil spills extraction,and some MODIS data were used to test if the method can perfect well on satellite data with lower resolution.Based on the above research,the main conclusions are as follows:(1)Even in the weak sunglint reflectection area,COCTS,CZI and VIIRS can identify the oil spills in Dongsha Island.The recognition ability of COCTS is not weaker than that of VIIRS;CZI can not only identify the oil spills,but also distinguish the oil slicks and oil emulsions,to provide useful information.On the CZI data,the dispersion of radiance of oil spills is larger than that of surrounding oil-free seawater,implying that optical remote sensing has the potential for the quantitative estimation of oil spills.(2)Based on testing of CZI data covering different areas,the method was proved to be effective in removing interference information caused by sunglint,image details and so on.This method can distinguish oil slick and oil emulsions under weak glint,and the Kappa coefficient shows it has high accuracy in extracting oil spills using CZI data.It is also applicable to be used in images with lower resolution,but the effect is not better than CZI due to the influence of mixed-pixel.(3)The HY-1C satellite has excellent radiometric resolution and high S/N.With the launch of HY-1D satellite,a network observation system of the HY-1C/D satellite will provide global images daily.They will play a more important role in future optical remote sensing of marine oil spills. |
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