The Detection of Oil in and with Ice Using Sar

The release of oil into the oceans represents an environmental hazard to wildlife, namely fish, birds and marine mammals, and can adversely affect humans that depend on the sea. Therefore considerable resources have been spent in cleaning up spills due to accident or design. To reduce the environmental impact it is important that spills be detected early so that remediation can be started. In temperate and tropical latitudes, volatile components of a spill evaporate rapidly and even the heavier components tend to disappear within months or a few years through breakup mechanisms involving solar UV, wind and wave actions, solubility, accretion to particulate matter with subsequent descent to the ocean floor and bacteriological processes. However, in arctic regions the natural processes are slowed down by the low temperature so that oil may persist for much longer and, over time, can have a much greater impact. Efficient remediation requires knowledge of the spill. If the offender is a ship discharging oily bilge water, the name of the ship must be determined unambiguously and its association with the spill established unequivocally; otherwise litigation will not succeed. Therefore timely detection is needed. Also an estimate of the size and nature of the spill is desirable to determine the extent of the cleanup resources to be allocated. The detection of oil in the open ocean is becoming operational. Appropriate sensors are available that can be located on satellites and aircraft to provide wide area and local surveillance respectively. There have been several review articles dealing with the various aspects of sensors and operations, such as Fingas [1], Fingas and Brown [2], Dickins [3] and Mahr and Chase [4]. Typically satellite borne Synthetic Aperture Radar (SAR) and/or Electro Optics (EO) sensors [5] are used for wide area surveillance and Maritime Patrol Aircraft (MPA) are used for verifying spills and, where necessary, for identifying ships and oil platforms. Aircraft may carry laser sensors to detect fluorescence from oil [6]. However, there are significant sources of false alarms and an operational system typically requires an operator trained in discrimination. Active sensors, such as radar and fluorosensors [4], [7] can operate in darkness. This is particularly important in the high arctic during the winter when it may be dark for the entire day. On the other hand, because an individual sensor may not be reliable and give rise to false alarms, a mixture of sensors is desirable and this includes arctic surveillance. During arctic winter months, a passive sensor may not be useful. A list of potential sensors for oil on open water and ice is provided in Table 1. The ground resolution of the sensors is important. In some cases the resolution cell is kilometers in size and small spills simply cannot be resolved. For open water there have been many studies of spills and some of these that utilize SAR are described in [8], [9], [10] and [11].