Chronic, Anthropogenic Hydrocarbon Discharges in the Gulf of Mexico

Satellite-borne Synthetic Aperture Radar (SAR) was used to obtain more precise estimates of the magnitude of the chronic hydrocarbon discharges described in qualitative pollution reports associated with the production and transportation network of the U.S. coast of the Gulf of Mexico. The National Response Center (NRCen) oil pollution reports were collected and filtered for the period of 2001 to 2012 to determine which of the reports coincided with archived SAR images. Some of the images covered multiple reports and some of the oil discharges described in one report could be observed in more than one image. In all, 177 reports could be investigated from 137 SAR images collected on or near the corresponding report dates. Further analysis found that oil slicks observed in 66 of these SAR images could be attributed to 67 of the reported incidents. Objective measurements indicated that the area of these transient oil slicks visible in SAR images was, on average, significantly larger than what was reported to the NRCen. The only recurring point source for oil slicks was the former site of the Taylor offshore platform. Here chronic, oil slicks were observed that were consistently much larger than other anthropogenic discharges. The SAR images of floating oil discharged from the Taylor site were verified by visual inspection from a boat and aerial photography. For some of the oil slicks discharged from the Taylor site, the accuracy of SAR images for detecting oil slick areas was validated by comparing SAR results to Landsat 7 Enhanced Thematic Mapper Plus (ETM+) and Moderate Resolution Imaging Spectroradiometer (MODIS) images. These results show that surveillance by SAR would improve accuracy for estimates of chronic anthropogenic oil pollution, particularly where continuous discharges are on-going.