In: Remote Sensing of Environment, Volume 45, Issue 2, August 1993, Pages 225-231.
by John W. Salisbury a, Dana M. D’Aria a and Floyd F. Sabins Jr.b
aDepartment of Earth and Planetary Sciences, Johns Hopkins University, Baltimore U.S.A.
bChevron Oil Field Research Company, La Habra, California U.S.A.
With all the interest on the Gulf Oil spill and recent accounts of the use by British Petroleum and others of Infrared Thermal Imaging to search for surface oil slicks, it seemed very timely to be sure we had included some links and summaries of articles dealing with the thermal Infrared optical properties of crude oil on seawater.
“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 ?m 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 ?m 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 ?m 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.
“Crude oil samples and analyses were kindly provided by D. K. Baskin of Chevron Oil Field Research Company. Seawater samples were provided by Doug Nash of the San Juan Capistrano Research Institute. Financial support was provided by the Solid Earth Science Branch of the National Aeronautics and Space Administration
.Address correspondence to John W. Salisbury, Dept. of Earth & Planetary Sciences, Johns Hopkins Univ., 3400 N. Charles St., Baltimore, MD 21218-2681.
Received 17 August 1992; revised 8 November 1992. Available online 7 April 2003.