THE DEVELOPMENT OF A REFLECTANCE SPECTRAL LIBRARY FOR CRUDE OIL AND REFINED PETROLEUM PRODUCT DETECTION on TERRESTRIAL SUBSTRATES

The Deepwater Horizon explosion and subsequent sinking produced arguably the largest oil spill in U.S. history. While the incident occurred in the Gulf of Mexico, one of the most prominent portions of the response is mapping the extent to which oil has reached thousands of miles of shoreline. Yet, the most common method of detecting oil remains visual spotting from airframes, supplemented by panchromatic/multispectral aerial photography and satellite imagery. While this imagery provides a synoptic view, it is unreliable.

Imaging spectroscopy provides more accurate petroleum detection and discrimination from water on terrestrial backgrounds. Utilizing spectral libraries, it can also perform material identification and discriminate some petroleum products from one another as a means of further classification and mapping spill extent. This effort collected spectral signatures of crude oils and refined petroleum products on a wide range of common terrestrial substrates and compared them to water on the same backgrounds. Crude oils consisted of a light, two intermediates, and a heavy crude. The refined products: E85 fuel, gasoline, diesel fuel, and a motor oil, were selected because they are common and because they span a wide volatility range. Substrates include concrete, asphalt, a calcite-dolomite crushed aggregate, grass with litter and underlying soil, bentonite, gypsum, a calcareous sand, a soil with high organic content, and two quartzic sands—Ottawa and a mid-Atlantic beach sand. They were selected for their ubiquity or the presence of absorption features that overlap hydrocarbon absorptions.

Liquid-substrate samples were left to age and regularly re-measured over the course of minutes, hours, and up to 100 days depending on volatility, establishing a relationship between evaporative loss for volatile and semi-volatile products and sample reflectance. The data outline temporal windows of opportunity and minimum detection thresholds for volatiles. The overall result is a publicly available spectral library in the reflective portion of the electromagnetic spectrum (400-2500 nm) for use in petroleum spill detection and response. The results establish a baseline for the use of imaging spectroscopy as a technique for confident, accurate petroleum detection in the terrestrial environment.