Supplementary file 1_Optical measurement of oil slick thickness using active interferometry.docx

Spills of liquid petroleum hydrocarbons are a growing concern worldwide, posing great risks to marine life and community services. Identifying and treating oil spills is operationally and scientifically challenging and compounded by the difficulty in accurately obtaining real-time measurements of the oil thickness slicks. Here, we present a method that allows precise real-time measurement of oil slick thickness, based on active optical interferometry. A series of laboratory experiments with common hydrocarbon pollutant types, namely crude oil and gas condensate, showed that our method yields precise thickness measurements for slicks in the thickness range 0.382 - 23.3 (μm), with an accuracy of 95%. The proposed spectral-domain active interferometric system enables direct and physically grounded retrieval of oil film thickness without mechanical scanning and without reliance on ambient illumination. In principle, the system can be adapted for deployment at sea, opening the way for real-time, in situ thickness measurements that will improve oil-spill mitigation efforts and contribute to a deeper understanding of processes at the ocean-atmosphere interface.