Oil spill detection in the Kazakhstan sector of the Caspian Sea with the help of ENVISAT ASAR data

Abstract

Oil pollution in the world’s oceans is predominantly caused by operational discharges from tankers (predominant oil dumped during cleaning operations). These discharges result in over 2 million tons of oil which are introduced annually comparable to one full-tanker disaster per week. Land-based sources such as urban waste and industrial discharges, which compass the ocean via rivers, are also a major contamination factor. The Caspian Sea is the largest inland water body on Earth without a direct connection to the world’s oceans, which makes it a unique water reservoir. This fact makes the Caspian Sea particularly vulnerable and subject to human influence, for example, pollution from shipping activities and oil transports by ships. The research study shows results from a monitoring campaign in northern and central parts of the Caspian Sea (Kazakhstan sector) for the period from 2005 to 2012 (April–October), based on visual interpretation of radar images from ASAR ENVISAT. Radar data (529 radar images) such as ASAR_WSM_1P and ASAR_IM_1P were obtained from the archives of the European Space Agency. In 529 ASAR ENVISAT images, 160 images were selected, on which 329 oil spills were detected. Examples of individual slicks were analyzed by visual image interpretation. The total surface of contamination for the entire study period was estimated by 822.66 km2. The average size of the oil spills ranged from 1.09 to 10.62 km2, in different years. The monitoring of oil spills over the Kazakhstan sector of the Caspian Sea could show that it is possible to state with certainty that the main source of oil pollution is shipping (confirmed by analysis of slicks form and clusters along shipping routes) and the most contaminated area is its southern part, where there is more intensive navigation in the direction of Aktau–Baku (Azerbaijan), Aktau–Turkmenbashi (Turkmenistan), and Aktau–Neka (Iran). In the northern part of the Caspian Sea, it was determined that a low number of spills could have been caused by fishing and marine activities in the development area of the Kashagan oil field. The result is based on comparing the contamination map and the map of navigation, as well as through an analysis of the geometry of the slicks. Monitoring results largely coincided with the results of work carried out in the region, and at different times for some of its sites. These findings based on the radar data showed advantages of ASAR ENVISAT satellite monitoring for the control of oil pollution on the sea surface.