Abstract
This study is devoted to a generalization of C-band Radarsat-2 and X-band TerraSAR-X synthetic aperture radar (SAR) data in the form of a diagram serving to easily identify mineral oil slicks (crude oil and emulsions) and separate them from the other oil slicks. The diagram is based on the multi-polarization parameter called Resonant to Non-resonant signal Damping (RND) introduced by Ivonin et al. in 2016, which is related to the ratio between damping within the slick of the short waves and wave breakings. SAR images acquired in the North Sea during oil-on-water exercises in 2011–2012 containing three types of oil spills (crude oil, emulsion, and plant oil) were used. The analysis was performed under moderate sea conditions (wind speeds of 2–6 m/s and sea wave heights of less than 2 m), the incidence angles of 27°–49°, and the signal-to-noise ratio (SNR) of −3 to 11 dB within slicks. On the diagram plane, created by the RND parameter and the Bragg wave number, the mineral oil samples form a well-outlined zone, called a mineral oil zone. For C-band data, the plant oil samples were clearly distinguished from the mineral oils in the diagram. Determination of the confidence level for the detection of mineral oils versus plant oil was proposed using the mineral oil zone boundaries. The mineral oil data with SNR within slicks better than 2 dB lay within this zone with a confidence level better than 65%. The plant oil data with the same SNR lay outside this zone with a confidence level of better than 80%. For mineral oil with SNR of −3 dB, the confidence level is 55%.
Highlights
Oil spill detection on the sea surface using remote sensing is important for operational surveillance of the oceans
This study was devoted to the generalization, in terms of the polarization parameter resonant signal Damping (RND), of the description of experimental slicks of mineral oil and plant oil observed in a wide range of incidence angles in different frequency ranges (C- and X-band) from the Radarsat-2 and TerraSAR-X satellites, at both relatively low and relatively high levels of the instrumental noise
One of the most valuable qualities of the polarization parameter RND is its connection with the theoretical model of electromagnetic scattering from the sea surface, and the co-pol HH-VV data only are needed to construct the RND parameter
Summary
Oil spill detection on the sea surface using remote sensing is important for operational surveillance of the oceans. SAR images obtained in single-polarization HH (horizontal transmit and horizontal receive) or VV (vertical transmit and vertical receive) mode are widely used in operational services. Natural phenomena, such as biogenic films (formed as a result of the activity of plankton and fish), thin ice, low wind zones, and rain cells can form a variety of look-alikes [1,2,3,4], frequently resulting in false detections. The statistics published by the CleanSeaNet organization for 2007–2011 show that 8866 general warnings of possible oil spills were produced after processing of single-polarization satellite SAR images, 2828 of which were checked by plane or ship, and only 745 were confirmed [5,6]. No more than 30% of the checked warnings were confirmed
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