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Thickness estimates and classification of surface oil using passive sensing at visible and near-infrared wavelengths

Passive optical sensing can provide information which complements that from other sensors routinely used in monitoring oil pollution. Greater reflection of sky radiance usually leads to thin oil appearing brighter than seawater. This positive sheen-water contrast is reduced when seawater reflectance is high. Absorption of light by thicker layers of oil suppresses water-leaving radiance, giving increasingly negative contrast. By exploiting this effect oil thickness has been estimated based on optical data from field experiments. Red to near-infrared radiance increases with oil thickness for light crudes, but not for heavier oils. This difference has been used to distinguish a light crude from two heavier oils during field experiments, and can also be seen in data from the Sea Empress oil spill.