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
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
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.
RADARSATs 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 RADARSATs 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
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
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.