The first few hours and the initial actions taken to combat an oil spill are crucial. Retaining the maximum amount of oil in the tanks of a vessel in distress, dispersing a freshly spilt slick in the open sea, setting up containment booms efficiently and in time, mobilising well trained, equipped and supported teams at the appropriate moment, at sea and on land all constitute actions which work towards the same goal: to reduce the impact on nature and human activities.
Participation of a shipowner
When the car carrier the Tricolor was shipwrecked in the Channel, the Scottish company Capital Bank and its insurers agreed to directly take on, under the direction of the French authorities, the removal of the vessel’s bunkers, the cutting up and removal of the wreck and the recovery of the parts of the cargo spread over the seafloor.
Aerial view of the wreck of the Tricolor with the Deurloo nearby (Smit Salvage vessel), strait of the Pas-de-Calais, France, December 2002
Participation of an oil group in response
When the oil tanker the Erika sank, the French company Total (the cargo owner), in accordance with an agreement with the Polmar authorities, took responsibility for:
• clean-up operations on sites that were difficult to access, requiring specially trained personnel
• treatment of the wreck, to eliminate all risks of future pollution from the fuel oil which was trapped in the wreck
• treatment of the 270,000 tonnes of soiled materials recovered by shoreline clean-up teams.
The general response coordinator should constantly be able to adjust the response effort to respond to a situation which may evolve very rapidly. For this, he needs not only clear objectives and precise operational procedures, but also detailed information on the situation and its potential evolution. This information should be constantly added to and adjusted. The pollution must continually be located, its movement and fate predicted and its extent estimated. Coordinators must determine which sites to prioritise for response, organise response actions and eliminate false alarms which may be likely to draw upon response resources. This is no easy task in daylight and fair weather. It is extremely challenging at night and in bad weather.
Specialised computer software exists which models the predicted drift of
a slick taking into account the weather forecast and the currents; however
the accuracy of these techniques is not perfect. They require, within a
defined time period, accurate inputting of:
• the day’s maritime and aerial observations (position of the pollution, comments on observations, flight plan, photos, imagery obtained by sensors...)
• data on seasonal or local currents provided by immersed drifting buoys (travelling below the surface) deployed in front of the pollution’s edge.
• data provided by drifting buoys on the edges of the slicks.
This data is transmitted between operational services by email, to avoid the delays which would be caused by the transmission of paper copies and the risks of error through transmission by telephone.
Comparison of signatures of slicks observed by satellite and plane. The SAR signature of the slick obtained by satellite...
... and the infrared signature obtained from the French Polmar 2 plane are in concordance with each other.
As soon as the pollution hits the shoreline, reconnaissance should be carried
out on land on a daily or twice daily basis. These reconnaissance efforts
should be conducted according to rigorous procedures by specially trained
personnel. They provide local response coordinators with accurate information
on the operational characteristics of the site (accessibility, waste storage…)
and on the characteristics of the pollution to be treated (impregnation
of sediment with oil, alternate layers of polluted sediment and clean sediment,
This information must also be transferred quickly and accurately from operators
French Customs’ Polmar 2 plane
Analysing the situation at sea and forecasting its evolution in order to effectively manage response at sea and inform the land authorities of dates and locations of arrivals of pollution is a very difficult job. Remote sensing technology cannot, unfortunately, resolve all difficulties.
It may take several days for satellites to pass over the same geographical location and the accuracy and authenticity of such data is variable, as with airborne radars. The data obtained by land-based stations can be sent to users about one hour after its retrieval. The basic remote sensing tools continue therefore to be planes and helicopters. These two modes can work either simply as a means of visual observation by day or can use specialised sensors allowing observation by night and in a wide range of meteorological conditions.
Did you know?
Remote sensing of oil slicks
Aerial remote sensing
Remote sensing from aircraft is a complementary method of observation, in addition to observation by the human eye. A number of different sensing systems are able to detect the presence of hydrocarbons on the sea surface, in certain sea and weather conditions. SLAR, the Side-Looking Airborne Radar, detects slicks according to differences in roughness (and therefore in reflection) of the water surface. Ultraviolet sensors can outline, in daylight, the borders of slicks. Infrared sensors identify the thickest areas of slicks by day and night. Microwave radiometers (MWR) distinguish and quantify slicks, however in practice their use remains relatively inaccurate. The laser fluorosensor, a heavier and less practical scientific tool, can distinguish the main oil categories, through the use of several reception channels.
The French Customs have two specially equipped planes for remote sensing pollution and recording data (Polmar 2 and 3). They are each fitted with a SLAR, a microwave radiometer, an infrared sensor and an ultraviolet sensor.
Satellite remote sensing
Satellites equipped with radar (SAR - Synthetic Aperture Radar) are a new means of detecting hydrocarbons at sea. Operational surveillance in the North Sea by SAR imagery has demonstrated that this observation technology, which is not affected by the level of cloud cover or daylight, enables aerial reconnaissance flights to be accurately orientated. After the example of airborne radar imagery, satellite radar imagery reliably shows discharge from vessels, thanks to the linear form of this discharge, over vast areas (to the order of 300,000 km2). However, the use of this imagery meets with three principal constraints. First, the radar imagery requires advanced analysis to avoid false alarms or detection errors. Secondly, the number of satellites is not yet sufficient to provide daily cover. Finally, the treatment of imagery in real time is possible, but at a non negligible price. The cost of surveillance per square kilometre is nevertheless considerably lower than that of aerial cover. However, aerial surveillance remains necessary as it can be both flexible and focused.
Prestige: a national slick drift
The quality of slick drift predictions during the Prestige disaster was improved by the creation of a specialised slick drift prediction committee in France, which was based at Cedre and drew together all the competent organisations (French Navy, Météo France, Ifremer, SHOM). The resulting good quality of predictions facilitated decision making by the authorities in charge of response and their communication with local councillors and the general public.
Information transmission in France during the Prestige accident