THERMAL INFRARED REMOTE-SENSING OF CRUDE-OIL SLICKS

It is important to develop a remote sensing technique for reliable detection of oil slicks for reasons of both oil exploration and environmental protection. Yet, unambiguous detection has proven an elusive goal. This article presents new thermal infrared spectra of oil slicks made from five different crude oil samples with a wide range of API gravities and compositions. After a brief outgassing phase, all oil slick spectra are quite similar and little affected by thickness, extended exposure to air or sunlight, and even by emulsification with seawater (mousse formation). Thus, oil slicks provide a remarkably unvarying spectral signature as remote sensing targets in the thermal infrared compared to other regions of the spectrum. This spectral signature in the 8-14 mum atmospheric window is flat, with an average reflectance of 4%. Seawater, on the other hand, has a spectrum that varies in reflectance with wavelength in the 8-14 mum window from 0.90 to 3.65%. In addition, we show that sea foam displays a reflectance spectrum quite similar to that of seawater in the 8-14 mum region, because the very high absorption coefficient of water in this wavelength region prevents volume scattering in foam bubbles. This results in a relatively uniform spectral background, against which oil slicks can be detected, based on their different spectral signature. Thus, thermal infrared multispectral remote sensing appears to offer a simple and reliable technique for aircraft or satellite detection of oil slicks.