Oil Spill Detection

The SeaDarQ oil spill detection system works on the principle that oil on the water surface reduces sea surface roughness and dampens wind waves. In the case of an oil slick, the sensitive receiver experiences a reduction in back scattered radar power creating dark structures in the radar images denoting the polluted area.

Conventional methods of measuring oil spills use airborne and satellite radar (SLAR and SAR), such as carried by the Netherlands Coast Guard aircraft and the European ERS satellites. While satellite and airborne radar have an advantage using a high angle (between 70 and 20 degrees) and high contrast between the unpolluted sea surface and the oil spill, they remain a single pass, single sweeping imaging technology which records only a moment in time. The SeaDarQ oil spill detection system, on the other hand, records a number of consecutive images and integrates these together to show a real time, continuous monitoring of oil spills. The amalgamation of images reduces problems of multiplicative noise and overcomes the low contrast and low angle of the radar. This is because one single image of the polluted area is not enough to register the low contrast between the sea surface and the oil slick. Typically, 64 revolutions of the antenna are required to filter and process reflections of the radar energy and to produce an image. In other words, it takes about one and a half minutes to produce a continuous real time image of an oil spill, after which a new image is automatically added.

It is possible to measure this contrast between the unpolluted sea surface and the oil spill when there are only capillary waves present (small ripples with a wavelength of typically less than a few cm). The ability of the SeaDarQ system to measure oil spills when there is only a small surface roughness represents one of the significant and unique advantages SeaDarQ holds over competitive products. When water waves are present (wave length 15m, wave height 0.5m), the SeaDarQ oil spill detection system works optimally, and can clearly identify areas of reduced sea surface roughness.

Characteristics of SeaDarQ Oil Spill Detection System:

Continuously monitor oil spills during the day and night

• Unlike satellite and airborne radar, the SeaDarQ system can continuously measure oil spills, because it is dependent on a radar source, rather than an external source such as sunlight.

Spill Area Determination

• Multiple polygons can be added to the screen, and can be drawn around the slick, detailing the surface area in square km or nautical miles.
• When using this tool during an incident, the appropriate clean up equipment can be directed to the most efficient location, thus reducing the environmental damage.
• The vertices of the polygon are geo-stationary and can be downloaded through a network connection, and this data can be integrated into a VTMS system. In this case, only the data is transmitted, which keeps the connection high speed and at a low cost.
• The mouse position on the screen provides real time data which is precisely calibrated in latitude and longitude. Distance to the antenna and bearing on the screen is also displayed. This information is available as output and can be used to control other sensors and equipment, such as cameras.

Prediction of drift

• Prediction of the current and movement of the oil slick is essential in clean up operations, and therefore the SeaDarQ system measures surface current 360 degrees around the antenna.
• The current can be measured around the oil slick when there is sufficient wave clutter resulting from disturbances of the water surface.
• The resolution of the area where the current is measured is adjustable, ranging from a grid size of 100 by 100 meters, to 1000 by 1000 meters.
• If weather conditions do not permit measurement of the surface current in real time, then it is possible to calculate the drift in time of the oil slick and use this as guidance for predicting the movement of the slick.

Range

• Detection range is dependent upon the radar type and the height of the antenna above the water surface. We specify a minimum height of 15 meters.
• Output power and input sensitivity of the radar, and water and weather conditions can also influence the detection range.
• As a guideline, the minimum detection range during poor weather conditions is 2 km.

Storage/Monitoring the evolution of oil spills

• Real time storage from raw radar lines is available to reproduce circumstances exactly during an oil spill or a cleaning operation. The SeaDarQ functionality is capable of operating on this recorded data, thus allowing access to surface current and wave information used for prediction of drift.
• The position of the vessel, its heading and AIS information are stored real time within the data also enabling circumstances to be reproduced. This can be used as legal evidence for later use in cases of illegal spills or accidents.
• As an example, if stored data is used to prove that a cleaning operating was successful, then the images of the area in reach of the radar should be compared with images from the same location recorded at a later date. If storage is performed 'looking' 180 degrees forward and storing a processed image every 5 seconds, almost two hours of data can be recorded, providing a sufficient impression of an operation.
• A snap shot function is also available to store screen images. These images, which can be presented as a layer, can be stored automatically in adjustable time frames, in a geo tiff format.

Requirements of the Oil Spill Detection System:

Vertically Polarised Antenna

• Several years of testing by TNO (Dutch non-profit Institute) and multiple tests by SeaDarQ using various different radars and has shown that the clutter sensitivity increases when using a vertically polarised antenna (VV).
• Independent testing of horizontal and vertically polarised antennas by Cedre in France, in 2007 demonstrated it was only possible to detect an oil spill using vertically polarised antennas.
• When a vertical polarised antenna is used with the SeaDarQ system, it is possible to detect disturbances of oil spills on the sea surface much more effectively, more reliably and longer in time.
• A specification of the SeaDarQ Oil Spill Detection System is that the antenna used must be vertically polarised.
• Standard navigation radars are equipped with a horizontal polarised beam (HH) in order to achieve a large target to sea clutter ratio of typically 6 dB or more. Despite this, it has been proved that a vertical polarised antenna is far superior than a horizontal polarised antenna for oil spill detection.
• SeaDarQ therefore produces its own dedicated VV antennas, with even shorter lengths so our oil spill detection operates with a much wider variety of weather circumstances. Even a film of oil or bilge water is visible using our vertical polarised antennas - something which can never be achieved using horizontal polarised antennas or antennas modified by foam.
• The dedicated VV antennas produced by SeaDarQ meet the highest standards, and in most cases will improve the results of the standard antenna.

Validation and Testing:

Multiple tests using the SeaDarQ oil spill detection system have successfully identified oil spills under a range of different weather conditions. In particular, the SeaDarQ system was used during the 'Prestige' incident in 2002 off the North Western coast of Spain. During this spill, the weather was extremely bad and there was no airborne support to assist the vessels in locating the oil. Further, due to the poor visibility, it was nearly impossible for the crew on board the cleaning vessels to detect and track the oil.

Only one vessel, of the North Sea Directorate of Rijkswaterstaat (RWS-DNZ) was equipped with a preliminary radar with an oil slick detection capability from SeaDarQ and was able to continue and direct cleaning operations. Even small slicks of 4 by 5 meters of oil were visible despite the strong swell and Atlantic conditions. The two Rijkswaterstaat vessels together removed around 80 percent of the total gathered oil, thus demonstrating the huge advantages the SeaDarQ system has over conventional methods for detecting oil and aiding cleaning operations.

SeaDarQ has also been used and has proved successful in other practical oil spill situations, such as the Tricolour in the French Channel in 2002, and The Margaret which sank outside the breakwater of La Spezia's port in Italy in 2005. Further, it has successfully detected oil slicks in The Mediterranean, The Baltic, The Atlantic and Persian Gulf. As an example, SeaDarQ has completed a number of oil spill tests in the United Arab Emirates. The range of the SeaDarQ system detecting these spills varied from 1 nautical miles to 3 nautical miles, and the amount of oil released ranged from 10 litres to 50 litres. It is important to note that the planned released oil spills for testing of the SeaDarQ system in this case took place during calm conditions at the height of the summer. During the winter and more rough wave conditions, the range for detecting oil spills will be increased.

Testing and validation of the SeaDarQ oil spill detection system have demonstrated and proved the system is capable of identifying:

• Radiagreen
• Diesel
• Ifo 30
• Fuel oil
• Kerosine
• Norwegian crude oil
• Bilge water
• Marine diesel