Oil Spill Detection by SAR Images: Dark Formation Detection, Feature Extraction and Classification Algorithms

Abstract

This paper provides a comprehensive review of the use of Synthetic Aperture Radar images (SAR) for detection of illegal discharges from ships. It summarizes the current state of the art, covering operational and research aspects of the application. Oil spills are seriously affecting the marine ecosystem and cause political and scientific concern since they seriously effect fragile marine and coastal ecosystem. The amount of pollutant discharges and associated effects on the marine environment are important parameters in evaluating sea water quality. Satellite images can improve the possibilities for the detection of oil spills as they cover large areas and offer an economical and easier way of continuous coast areas patrolling. SAR images have been widely used for oil spill detection. The present paper gives an overview of the methodologies used to detect oil spills on the radar images. In particular we concentrate on the use of the manual and automatic approaches to distinguish oil spills from other natural phenomena. We discuss the most common techniques to detect dark formations on the SAR images, the features which are extracted from the detected dark formations and the most used classifiers. Finally we conclude with discussion of suggestions for further research. The references throughout the review can serve as starting point for more intensive studies on the subject.

Dark-spot detection from SAR intensity imagery with spatial density thresholding for oil-spill monitoring

“…The main sources of marine oil pollution are discharges coming from ships or offshore platforms, which can be accidental or deliberate (Topouzelis, 2008). On August 4, 2006, oil leaking from M/V Westwood Anette at Squamish dock terminal, just north of Vancouver, British Columbia, Canada, costs $1 million to cleanup.…”

“…Usually, for oil spill detection, large swath widths are chosen at the expense of lower resolution because it is in our interest to cover a large area even if very small oil spills cannot be detected. The commonly used SAR sensors for oil spill monitoring from literature include RADARSAT-1, ENVISAT, ERS-2 (Brekke & Solberg, 2005;Topouzelis, 2008). Table 1.1 presents satellite SAR sensors that have been commonly used for oil spill monitoring.…”

Incidence angle normalization of Wide Swath SAR data for oceanographic applications

“…For example, the first crucial step for mesoscale oceanographic phenomena detection and classification (e.g. oil spills, eddies, currents, or fronts) is the identification of dark objects in SAR images [4,9,10]. This step is extremely difficult in wide swath images due to backscatter decrease from near to far range.…”

Dark Spot Detection Using Intensity and the Degree of Polarization in Fully Polarimetric Sar Images for Oil Polution Monitoring

“…Due to the speckle effects, intensity values may show considerable variability, even in a uniform region (Oliver and Quegan 2004). (2) Based on the local sea state, the type of the oil spill, the resolution and incident angle of the SAR imagery, the contrast between the oil spills and sea clutter can vary (Topouzelis 2008). These difficulties can interrupt getting to the comprehensive and fast solution.…”

“…Due to the fact that oil spills reduce backscattering from the sea surface, oil slicks appear as dark regions on SAR imagery which contrast with the surrounding water surface (Topouzelis 2008). However, other phenomena which are known as look-alikes such as low-wind areas, rain cells and so on can generate dark patches on the sea clutter (Alpers et al 1991).…”