Floating Oil on Seawater, In Situ Thermal Structure, Thickness, and Remote Sensing—Part 1: Laboratory Study

Thermal infrared (TIR) remote sensing shows potential for oil spill response. Most TIR remote sensing uses the brightness temperature contrast, ΔT_B, between oil and oil-free water. This study evaluates the potential of remotely sensed ΔT_B to quantify oil thickness through a series of lab experiments that measured actual surface temperature contrast, ΔT, for a Denver/Julesburg Basin crude oil. Specifically, TIR and visible video cameras imaged oil layers of different thicknesses, h, floating on seawater. Also, fast thermocouples collected high resolution (to ∼10 μm) vertical profiles. A novel deconvolution approach corrected for thermocouple time response. Slope changes in the profiles indicated the oil–water interface location. Experimental illumination was for full sunlight (outdoors) and incandescent light (indoors) for emulsified and unemulsified crude oils. Oil slicks were classified by distinct behaviors with a transition at h∼1 mm. Thinner than this transition, ΔT was strongly sensitive to h, with oil temperatures decreasing monotonically with depth in the slick. In contrast, oil slicks thicker than this transition featured an internal temperature peak with ΔT weakly sensitive to h. This peak isolates the oil below the peak from affecting surface temperatures. Thicker slicks also were associated with a thin warm air layer that increasingly developed with h. This study highlights the potential for deriving oil slick thickness from ΔT_B and the need for an improved understanding of solar insolation absorption and heat transfer for a range of oil and oil emulsion slicks.