HY-1C COCTS and CZI observation of marine oil spills in the South China Sea

An ocean color satellite of China (Haiyang-1C, HY-1C) was launched on September 7, 2018, equipped with several optical sensors, such as the Chinese Ocean Color and Temperature Scanner (COCTS), Coastal Zone Imager (CZI), and ultraviolet imager. These instruments were tested in orbit for 6 months and used in ocean and coastal zone environmental monitoring in June 2019. The 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 on February 20, 2019 was used as a case study. COCTS and CZI captured the oil spill, and the oil spill area was scanned using the Visible Infrared Imager Radiometer Suite (VIIRS) and Moderate Resolution Imaging Spectroradiometer (MODIS Terra & Aqua) on the same day. The angles (between the viewing direction and the direction of mirror reflection, θm) of COCTS, CZI, VIIRS, and MODIS Terra and Aqua images were extremely small, indicating that sunglint reflectance in these images can be ignored. Therefore, the light absorption and backscattering characteristics of oil spills and surrounding oil-free seawater account for the differences among the images. In other words, these light signals can only weakly detect marine oil spills compared with strong sunglint reflection. However, if backscattering can be distinguished, it can be useful in the identification of various types of weathered oil. COCTS, CZI, and VIIRS capture marine oil spills with high radiometric resolutions and signal-to-noise ratios. Moreover, oil spills form oil emulsions and non-emulsified oil slicks, which can be distinguished by CZI due to its high spatial resolution (~50 m). Uncertainty analysis of COCTS and CZI shows that the difference between an oil spill and the oil-free seawater of COCTS or CZI is obvious, implying that CZI can be used in estimating the volumes of oil spills. In the near future, the same sensors in the HY-1D satellite will be available, and a network observation system of the HY-1C/D satellite will provide global images daily. This resource will likely play an important role in future ocean color remote sensing. © 2020, Science Press. All right reserved.