Topic 3d - Oil spill monitoring

Satellite data are used to provide decision support for oil spill response during accidents that release large volumes of oil into the sea.

The data are used in two ways: optical and SAR data from satellites and aircrafts provide information on; the location, extent and thickness of surface oil. While other sensors provide wind, wave and current measurements that can be used as input into numerical models to predict how the spill will evolve. This is used, for example, by the European Maritime Safety Agency (EMSA), to provide an oil spill monitoring service that alerts the authorities when an oil slick indicates a breach of regulations to prevent oil pollution.

Oil spill detection

The main satellite sensor for oil spill detection is Synthetic Aperture Radar (SAR). It has a sufficiently high resolution to reveal relatively small areas of surface oil, and can ‘see’ through clouds.

How does it work?

  • Oil spill detection works at wind speeds between 3 and 10-12 m/s.

  • Oil appears darker than water in SAR images because it calms the wind-ripples that make the sea surface appear bright in SAR images when wind speeds exceed 3 m/s.

  • Above 10-12 m/s the oil is increasing mixed into the water and disappears.

Satellite data for oil spill detection are used in different ways:

  1. In support of oil spill response during major accidents (e.g. Deepwater Horizon oil spill)

  2. Routine monitoring of shipping lanes, ports and off-shore installations to check on compliance with discharge limits (e.g. EMSA Clean Sea Net)

  3. In environmental impact assessments: either to assess the impact of new infrastructure (ports, oil refineries, off-shore installations) or to assess the impact of large scale accidents.

Featured Educators:

  • Dr Val Byfield

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Don’t forget you can download the video and transcript with the links on the right.


Deepwater Horizon ASAR

Envisat ASAR image earlier the same day (ascending overpass) shows the oil as much darker than the surrounding water due to oil damping of cm scale wind ripples. The arrows point to features of thicker and thinner oil which could be seen in the optical image, but are not distinguishable in the SAR image. On the other hand, the dark area (oil) is larger than in the optical image, because SAR is sensitive to surface oil films that are too thin to be observed in optical images. Credit: ESA LearnEO

Deepwater Horizon MERIS 1 month later

the spill a month later as the oil had entered the Gulf of Mexico Loop Current. In this image the oil is found in the sunglint zone, and therefore appears brighter than the surrounding water because it reflects more of the direct sunlight. A transition zone marks where the oil-water contrast shifts from positive (brighter oil) to negative (darker oil).

Deepwater Horizon MERIS 1

Annotated Envisat MERIS image of the oil spill just over a week after the explosion on 20 April 2010. Thick oil is visible as brownish red stripes, surrounded by an area of oil with intermediate thickness, and thinner oil, which is darker than the surrounding water

Oil spill monitoring

SAR image with coloured lines marking the location of oil slicks observed in a time series of SAR images. These mark the locations of thin oil slicks leaking from the fuel tanks of the Volgoneft, which broke up and sank the previous November. As the oil from the tank resurfaced, the oil spread in a downwind direction. Because the wind direction varied over the 2 month period, the lines marking the oil location in each image form a star centered on the location of the wreck. Credit: Space Research Institute of Russian Academy of Sciences (IKI-RAS).