Detecting oil on water using polarimetric imaging

Integrity Applications Incorporated (IAI) collected electro-optical polarimetric imagery (PI) to evaluate its effectiveness for detecting oil on water. Data was gathered at multiple sun angles for vegetable oil and crude oil to demonstrate PI sensitivity to different liquids and collection geometries. Unique signatures for oil relative to water were observed. Both oils consistently displayed higher degree of linear polarization (DOLP) values than water, which was expected based on the lower index of refraction of water (1.33) relative to vegetable oil and crude oil (1.47 and 1.47-1.57, respectively). The strength of the polarimetric signatures was found to vary as a function of collection angle relative to the sun, with peak linear polarizations ranging from 40-70% for crude oil and 20-50% for vegetable oil. IAI found that independently-scaled DOLP was particularly useful for discriminating these liquids, because it demonstrated the least sensitivity to collection angle, compared to other PI products. Specifically, the DOLP signature of vegetable oil was approximately 20% lower than for crude oil, regardless of collection angle. This finding is consistent with the lower index of refraction values for vegetable oil compared to crude. Based on the promising results presented here, IAI recommends further testing and development of PI for oceanic remote sensing applications such as oil spill/leak detection and for supporting oil cleanup efforts. With additional work, PI may also be applicable to other oceanic environmental issues such as detection of agricultural runoff or effluent from industrial facilities or watercraft.