Geographic Extent, Temporal Persistence and Mapping of Floating Oil from the the Exxon Valdez Oil Spill: 1989

Information about this project comes from the original project proposal submitted in October, 1989. No Final Report is available.

The general mission of this Natural Resource Damage Assessment floating oil mapping effort was to document the extent, amount and persistence of oil resulting from the EXXON VALDEZ oil spill. Maps have been produced on a regular basis showing the location of oil from aerial surveys from the first day of the spill on March 24, 1989. While the aerial overflight mapping effort has been reduced since mid May, to one flight a day from two or three, there are still regular aerial overflights being performed to monitor the location and extent of oil in the water. Another source of information that yielded answers on the extent of floating oil was satellite imagery. The data source used here consists of imagery obtained from a variety of polar-orbiting satellites. The function of the satellite imagery portion of this study is to revise digital filtering techniques to remove noise and to perform digital enhancements to improve the identification of oil. In addition, the satellite imagery will be enhanced to provide oceanographic data useful in determining the oil's trajectory as well as its weathering, mixing with suspended sediments and related evolution. Finally, there is a possibility that some of the satellite imagery will yield information that will document the extent of oiled beaches.

The aerial overflights produce three basic data types. The first type is a hard copy of a nautical chart with observers notes and markings indicating the location and extent of the oil as well as the flight track taken by this crew. The second data type is video tape showing the oil on the water. The third data type is a written report from the observers with any other observations they may have as well as weather information indicating the observing conditions. In many instances still photographs also exist from the flight. All of this information is combined to ensure the accuracy and reliability of the information.

The satellites produce image format data of the earth's surface in a variety of wavelength bands ranging from blue visible light to the thermal infrared Some of these bands are useful for the identification of oil while others are useful for identification of suspended sediment, the thermal regime, and possibly large concentrations of plankton. The oil signature in most cases is only slightly different from that of the ocean, requiring sophisticated digital image enhancement techniques to separate the two. It is possible that the oil signature will be found to change over time as a result of its weathering. Other techniques are used to display the identified oil relative to regions of suspended sediment where the oil may have become sufficiently heavy to have become submerged.