Detection of oil spill frequency and leak sources around the Oil Rocks Settlement, Chilov and Pirallahi Islands in the Caspian Sea using multi-temporal envisat radar satellite images 2009–2010

Abstract

The main goal of this research was to detect oil spills, to determine the oil spill frequency, and to approximate oil leak sources around the Oil Rocks Settlement, the Chilov and Pirallahi Islands in the Caspian Sea using multi-temporal ENVISAT Advanced Synthetic Aperture Radar Wide Swath Medium-resolution images acquired in the period of 2009–2010. The processing of ENVISAT satellite images for oil spill detection included the following stages: filtering of images for noise reduction and imagery enhancement, preliminary segmentation for detection of dark features, interactive visual interpretation for the discrimination among other oil spill look-alikes, computation of oil spill frequency, and approximation of oil leak sources. The analysis showed that the appearance of the oil slicks in the radar imagery significantly depends on the Caspian Sea wind speed. The best wind speed conditions for the detection of oil spill were determined to be 2.5–14 m/s. The hot spot areas of detected oil spill frequencies for 2009–2010 were the following: 2–25 (4,658.83 sq. km.), 26–45 (302.83 sq. km.), 46–75 (77.95 sq. km.). The most critical oil leak sources were observed around the Oil Rocks Settlement. The exponential regression analysis between wind speeds and oil slick areas in 2009 with R2 equal to 0.61 showed that larger oil spill areas were observed with lower wind speeds. The spatiotemporal patterns of currents in the Caspian Sea explained the multi-directional spatial distribution of oil spills around the Oil Rocks Settlement.