Visible Near-Infrared Reflection Spectrum Characteristics and Angular
Effects of Sea Ice Contaminated by Ship Oil Spills
XU Jian-kang1, LIU Bing-xin1, 2*, DU Yu-long1, LI Ying1, 2, LIU Peng1, 2, CHEN Peng1, 2
1. School of Navigation, Dalian Maritime University, Dalian 116026, China
2. Environmental Information Research Institute, Dalian Maritime University, Dalian 116026, China
Abstract：With the opening of the Arctic shipping route, the number of vessels traveling to and from polar ice regions has been increasing yearly, leading to an increased risk of oil spills in the ice zone. Difficulties in cleanup and long-lasting pollution characterize oil spills in icy areas. Therefore, the development of fast and accurate monitoring methods has become an important approach to improving cleanup efficiency and reducing pollution hazards. Remote sensing technology has been widely applied in monitoring oil spills in open waters, but there is relatively less research on monitoring oil spills in ice-covered seas. In particular, there are few reports on the reflection spectral characteristics of oil-contaminated sea ice and their variations with viewing angles.In this study, through simulated experiments of oil spills on sea ice, visible-near-infrared reflection spectra of oil-contaminated sea ice were measured at different observation zenith angles and relative azimuth angles. Measurements were taken at intervals of 10° for zenith angles ranging from -50° to 50°, and relative azimuth angles included 0°, 90°, 180°, and 270°. Analyzing the spectral standard deviation before and after ice pollution, the wavelength of 560 nm with the most significantdifference was selected as the characteristic wavelength for identifying oil-contaminated sea ice. This study constructed a kernel-driven model to explore the relationship between the reflectance difference of the characteristic wavelength and the geometric variations of observations. This Ross Thick-Roujean-r-RPV model considered the forward scattering characteristics of sea ice. The model was tested using measured data, and the fitting errors in the principal plane and vertical principal plane were 0.004 62 and 0.004 16, respectively, showing better fitting performance than commonly used kernel-driven models such as Ross Thick-Li sparse, Ross Thick-Li sparse R, Ross Thick (QU)-Roujean, and Ross Thick (QU)-Li sparse R-r-RPV. Using this model, the study further simulated the angular effects of the reflectance difference in the characteristic wavelength of sea ice before and after oil pollution under different observation geometries. The results showed that under the same observation geometry, there were differences in the reflectance spectra of sea ice before and after pollution, with polluted sea ice having lower reflectance than clean sea ice. Additionally, clean sea ice peaked in the wavelength range of 1 013~1 196 nm, disappearing after pollution. When the azimuth angles of observation were different, there were also differences in the reflectance of sea ice, characterized by an increase in the forward direction with increasing observation angles and a decrease in the backward direction with increasing observation angles. In the principal plane direction, the reflectance increased initially and then decreased with increasing observation angles. The largest spectral difference was observed at a zenith angle of 50° and a relative azimuth angle range of 250°~290°, which is most favorable for extracting oil spills in sea ice. The research findings of this study can provide a reference for the selection of bands and observation geometries for monitoring sensors of oil spills in icy regions for ships.
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