AVHRR observations of Persian Gulf oil spills

Visible and infrared (IR) imagery taken by the Advanced Very High Resolution Radiometer (AVHRR) aboard the NOAA polar-orbiting satellites, and in-situ data from aircraft and field observations are used to examine oil spills during the 1991 Persian Gulf War. In AVHRR IR imagery from January 19 to February 10, 1991, several "hot spots" were detected in the vicinity of the center of the larger oil spill regions. These "hot spots", with apparent IR-skin temperatures of about 2-4°C above the surrounding sea surface temperature (SST) in daytime, were embedded in a region with IR temperatures 1-3°C below the surrounding SST. This is consistent with previous laboratory IR observations of varying oil layer thickness. The "hot spots" weakened and disappeared at night. The IR oil spill signal became very weak after February 15. Only under favorable ocean and weather conditions did the AVHRR visible channel show patches of contrasting albedos in the oil spill regions. Using specialized image enhancements, thick and thin oil layers and the oil/water boundary in the IR imagery could be inferred. The IR-detected oil spill areas corroborated well with surface observations.