Abstract
Oil spill detection services based on satellite synthetic aperture radar (SAR) frequently detect oil slicks close to platforms due to legal releases of produced water. Separating these slicks from larger releases, e.g., due to accidental leakage is challenging. The aim of this work is to investigate the SAR characteristics of produced water, including the typical appearance in HH/VV data, possible variations with oil volume, and limitations on detectability. The study is based on dual-polarization TerraSAR-X data collected with constant imaging geometry over one platform in the North Sea. Despite the low oil content (volume percentage of 0.001%–0.002% in this data set), produced water is clearly detectable, with median damping ratios around 3–9 dB. Produced water is detected here in wind speeds of 2–12 m/s, with reduced detectability above ca 9 m/s. Hourly average release volumes with an oil component as low as 0.003 m 3 are detected. The damping ratio, polarization difference, and co-polarization power ratio are investigated and show no clear correlation with released oil volume. However, some indications of trends such as increasing signal damping with oil volume should be further investigated when data over larger release volumes are available. When comparing the properties of the entire slick with the most recently released part, similar or slightly higher damping ratios were found in the full slick case.
Highlights
Satellite synthetic aperture radar (SAR) has been used for operational surveillance of large sea areas and the detection of marine oil spills for decades
Single-polarization parameters related to geometry, shape, contrast, gradients, and contextual information have been used for oil spill detection and oil vs. look-alike discrimination [2]
Parameters are compared to in situ measurements in order to investigate the effect of increasing oil volume on the SAR signature, and in particular on the oil-sea contrast in damping ratio (DR) and polarization difference (PD) and to explore if there are any parts of the slick that affect the co-polarization power ratio (CPR)
Summary
Satellite synthetic aperture radar (SAR) has been used for operational surveillance of large sea areas and the detection of marine oil spills for decades. From Norwegian platforms alone, more than 133 million m3 of PW was released in 2018, with an average oil concentration of 11.2 g/m3 [1] Separating these slicks from other types of oil spills is difficult, the proximity to a platform can be used as an indication. The objective of this work is to investigate the characteristics of SAR signatures of PW, including their typical appearance in HH/VV SAR data, possible variations with oil release volume, and limitations on detectability in terms of oil releases and wind conditions. The study shows that even very small oil concentrations (volume percentage of 0.001%–0.002% in this data set) produce clearly detectable SAR signatures, with damping ratios around 3–9 dB, which is comparable to observations over high concentration oil releases.
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