SAR

(Above) ERS-SAR image of the Strait of Gibraltar showing a well developed train of internal oceanic solitary waves propagating eastward.

Synthetic Aperture Radar (SAR) systems provide high resolution imagery of the Earth's surface, independent of light and cloud conditions. The technology for processing and extracting geophysical quantities from SAR data is mature, with validated algorithms and models for important oceanographical parameters like wind, waves, current and slicks. This makes SAR imagery suitable for a number of marine applicatioms, ranging from support of near real time operations to use in long term planning.

SAR systems take advantage of the of the long range propogation characteristics of radar signals and the complex information processing capability of modern digital electronics to provide high resolution imagery. SAR aboard the European Remote Sensing satellites ERS-1 and ERS-2, which were launched in 1991 and 1995, respectively, provides images of the earth's surface with a resolution of 25m. RADARSAT, from a Canadian Space Agency funded programme, provides an additional source of SAR data. RADARSAT collects data in at a resolution of between 10 -100m.

In 2002, the European Space Agency will launch ENVISAT, an advanced polar-orbiting Earth observation satellite, which will provide measurements of the atmosphere, ocean, land, and ice over a five year period. The ENVISAT satellite has an ambitious and innovative payload that will ensure the continuity of the data measurements of the ESA ERS satellites.

The ERS-1 mission is split into several phases with different repeat cycles
(3, 35 or 168 days) that are optimised for different applications. ERS-2 has a repeat cycle of 35 days. RADARSAT has a 24 day repeat cycle with a 500km swath width. The wide swath width would allow repeat coverage of the Arctic every 3-7 days. The new ENVISAT SAR, ASAR, has a repeat coverage of 35 days and a swath width of 400km.

 

SAR Capabilities

  • Wind Field & Sea State
    SAR can provide detailed quantitative local wind information. Sea state estimates include high resolution (1-10km) near surface wind field (wind speed, direction) maps and high resolution wave field (amplitude, wavelength, direction) maps.
  • Current & Frontal Features
    Current feature estimates including surface current gradients, converging and diverging current systems, mesoscale eddies, internal waves and shallow water bathymetry.
  • Slicks
    Slick estimates including determinations and classification of low scattering areas into presence of natural film, oil spill and seepage.
  • Sensor Synergy
    Combining data from several sensors and satellites can make an important contribution to coastal ocean monitoring. In addition to increasing the spatial and temporal coverage, this synergy also offers opportunities to advance the analysis and interpretation of remote sensing data.

(Above) Internal solitary waves and rain cells in the Andaman Sea