SAR provides an option for acquiring information on the open ocean and coastal region. In particular, RADARSAT-1 can provide information for a variety of applications including ship location, oil spill detection and monitoring, aquaculture site identification, wind and wave retrieval and ocean pattern identification. This information can be useful for offshore engineering activities, operational fisheries surveillance, and storm forecast operations.

Coastal zone monitoring implies observation of the interaction of oceanographic and atmospheric phenomena with human activities in the near-shore region. The key issues include the delineation of the coastline, defining areas of erosion and sedimentation, mapping the inter-tidal vegetation, and identifying areas of human settlement and accompanying activities. The coastal zone is an environmentally sensitive region subject to increasing stress from economic development and government agencies concerned with the impact of human activities in the near-shore region are looking for new data sources with which to monitor this region.

An excellent coastal zone application of radar is aquaculture site monitoring. These man-made structures provide higher signal returns than the surrounding water. RADARSAT-1 projects in the Pacific Ocean have successfully identified aquaculture sites such as shrimp ponds and fish farms located in environmentally sensitive inter-tidal zones. The growth of the fish farm industry in regions of mangrove forests, and the resulting negative impact on the health of the forests, is of concern to government agencies. RADARSAT-1 has been able to provide a new source of information.

Open ocean applications include the study of large scale ocean features manifested at the ocean surface by the interaction of wind driven currents with the marine boundary layer. The principle scattering mechanism for ocean surface imaging is BRAGG scattering, whereby the short waves create spatially varying surface patterns. The backscatter intensity is a function of the incidence angle and radar/wavelength, as well as the wind and wave condition at the time of imaging. For RADARSAT (5.3 cm wavelength) the surface waves that lead to BRAGG scattering are roughly equivalent to its wavelength. These short waves are generally formed in response to the wind stress at the marine boundary layer. Modulation in the short waves may be caused by long gravity waves, variable wind speed, and surface currents associated with upper ocean processes such as eddies, fronts, and internal waves. These variations result in spatially variable surface roughness pattern which is imaged by the SAR.

RADARSAT’s flexible viewing geometry permit a wide range of ocean applications. For example, a smaller incidence angle, such as those of Standard beams 1-3, are suitable for imaging open ocean and coastal features such as man-made structures, oil spills, current shears, internal waves, shallow water and bathymetry effects. By using RADARSAT’s larger incidence angles, the ocean background clutter effects are reduced, improving the detection of ships, coastline and ice edges. For example, a ship is a bright point target against the ocean background clutter and can be detected using image thresholding techniques. However, as the ocean clutter increases with increasing wind speeds, ship detection becomes more difficult. At winds speeds greater than 10 m/s it is difficult to detect small fishing vessels. This relationship with wind speed is a critical factor for ship detection as well as oil spill mapping and feature detection. As the wind speeds increase, the radar cross section of the ocean increases, reducing the contract between the feature of interest and the surrounding ocean.

Ship detection is a good example of the operational role of radar. Ships may be detected for a wide range of ship sizes and under a variety of sea-state conditions. Radar can infer ship size, and if a wake is present, its speed and direction of travel. It should be noted that an HH polarization is less sensitive to wake detection and in studies to date, wakes are infrequently detected. Potential users of this information include agencies who monitor ship traffic, authorities responsible for sovereignty and fisheries surveillance, as well as customs and excise agencies charged with stopping illegal smuggling activities.

Oil slicks and natural surfactants are imaged through the localized suppression of BRAGG scale waves. Under calm conditions, natural surfactants may form over large areas of the ocean, along current boundaries, and in areas of upwelling. The accumulation of natural surfactants at these boundaries can delineate the general circulation pattern and are visible on the radar image as curvilinear features with a darker tone than the surrounding ocean. Oil spills also have a darker tone with respect to the surrounding ocean background. The detection of an oil spill is strongly dependent upon the wind speed. At wind speeds greater than 10 m/s, the slick will be broken up and dispersed, making it difficult to detect. Another factor that can play a role in the successful detection of an oil spill is the difficulty in distinguishing between a natural surfactant and an oil spill. Multi-temporal data and ancillary information can help to discriminate between the two phenomena. Wind shadows near land, regions of low wind speed, and grease ice can also be mistaken for oil spills and ancillary data (or an experienced user) are necessary to distinguish between these features and a spill.

• Wide area coverage (RADARSAT Wide and ScanSAR beam modes) is useful for monitoring and surveillance applications including ship traffic, fisheries monitoring, oil spill mapping, and ocean circulation mapping.


• Intermediate area coverage (RADARSAT Standard beam mode) is useful for monitoring ship traffic, near-shore fisheries activities, oil spill mapping, and inter-tidal feature mapping.


• Small area coverage (RADARSAT Fine beam mode) is useful for harbour traffic monitoring, aquaculture site location and small spill mapping.


• High frequency temporal coverage over selected areas can be achieved by varying the beam position and using the extended beam mode options.


• Small incidence angles are optimum for oil spill detection. Detection will also depend on the spill size, sea state conditions and image resolution. With the better than expected noise performance of RADARSAT, higher incidence angle modes can also be considered.


• Large incidence angles are optimum for ship target detection. Detection depends on ship size, and type, heading with respect to look angles, and sea state conditions at the time of imaging.


• Shallow incidence angles are optimum for the detection of aquaculture cages and weirs. Detection will also depend on the size and configuration of the pens, and sea state conditions at the time of imaging.


• The effects of bathymetry are visible in near-shore regions under light wind conditions. Small incidence angles are better suited to imaging inter-tidal features such as mudflats, shoals and sandbars.