Introduction: Remote sensing is useful in several modes of oil spill control, including large area surveillance, site specific monitoring and tactical assistance in emergencies. Remote sensing is able to provide essential information to enhance strategic and tactical decision-making, potentially reducing incidence of spills by providing a deterrent factor, decreasing response costs by facilitating rapid oil recovery and ultimately minimising impact. Marine oil spills can be separated into two categories of relevance to the type of remote sensing technology which might be used to detect and respond to the incident. A first category is non-accidental discharges, which can include incidental losses from vessels due to hull or equipment leaks, as well as oil discharged intentionally during deballasting and tank-cleaning activities. While these non-accidental discharges tend to be small in themselves, they are frequent and contribute much more to the overall introduction of oil to the marine environment than accidental spills, and are of increasing international regulatory concern. Accidental spills are much less frequent, but typically involves much larger releases of oil. Such oil spills are high profile events for which rapid and effective emergency response is needed to contain and recover the spilled oil. In many countries, an appropriate and effective response capability is required by law, such as demanded by the Oil Pollution Act of 1990 in the US, as well as by recent amendments to the Canada Shipping Act in Canada. There is a growing recognition that using remote sensing, especially airborne, to aid cleanup response efforts can mitigate the effects of oil on the environment, as well as reduce cleanup costs. Airborne remote sensing sensing in the support of spill response operations has a mixed level of interest by spill responders when viewed globally. In the US, for instance, airborne remote has had varying degrees of success in meeting operational expectations, and thus is not yet fully integrated into national, regional and area response plans and operations. By comparison, the record of successful use in the UK, for instance, is such that remote sensing support is contracted by the UK Coast Guard on a stand-by basis and used routinely when a significant spill occurs. As another example, airborne remote sensing technologies are now being adopted by the Australian Maritime Safety Authority to support its spill response actions. Low altitude aircraft have proven to be the most effective tactical method for obtaining information about spills and assisting in spill response. Combined with accurate oil drift computer model forecasting, these two methods were the primary strategic tools used for environmental response planning during the IXTOC-1 and Arabian Gulf spills, although less useful for guiding tactical operations (Pavia and Payton, 1983; Cekirge et al., 1992). Conversely, essential tactical support was provided by aerial remote sensing for the application of dispersants, a major spill response in the Sea Empress spill in Southwest Wales (Harris, 1997; Lunel et al., 1997). Currently, the use of imaging satellites for spill response is restricted because of limited spatial resolution, slow revisit times and often long delays in receipt of processed image data. The topic of oil spill monitoring by imaging satellites has been reviewed by Bern (1993a,b). There are significant advances being made, however, to increase resolution and coverage, as well as in the speed of image product delivery. Sensing oil on water by satellites appears best suited for routine surveillance purposes. There are synergisms in protecting the environment and property from oil spills which can be achieved by an integrated approach which draws on the remote sensing advantages of airborne and satellite imaging technology. There are many potential users of such remote sensing information, in government and private sector organisations. Government authorities use such information in surveillance, for example in the North and Baltic Seas, detecting spills when they occur and for identification of the spiller, which could be a vessel discharging illegally. Many government organisations also maintain an organised oil spill response capability, which would be supported by remote sensing information in oil spill response operations. The private sector includes the primary oil industry operating globally, and oil transporters, which carry responsibility and potential liability in the event of a spill. Other potential users are oil spill response organisations which might offer a sub-contracted remote sensing capability to their clients. Other private sector groups include the insurers for the shipping industry, who are directly and immediately interested in keeping both the costs of the response and oil spill impact damage as low as possible. The news media is a additional potential user, interested in quality graphical representation of the oil spill, as is true for any disaster event.
COMPARATIVE METHODOLOGIES FOR ESTIMATING ON-WATER RESPONSE COSTS FOR MARINE OIL SPILLS
