Detection and Classification of Ocean Eddies Using ERS-1 and Aircraft SAR Images

                   D. Lyzenga and C. Wackerman
           Environmental Research Institute of Michigan
                  Ann Arbor, Michigan 48108 USA



  The interaction of ocean waves with surface currents having a
  significant horizontal shear causes either an amplification or
  a reduction of the surface wave spectral density, depending on
  the wave propagation direction.  The radar backscatter modulations
  that result from this interaction are therefore also a function
  of the radar look direction relative to the direction of the
  current shear.  This effect causes distinctive patterns in radar
  images of the ocean surface which can be used to detect the
  presence of ocean eddies and to determine the direction of their
  rotation.

  These concepts have been applied to a set of ERS-1 and aircraft
  SAR images collected off the coast of Norway on October 9, 1993.
  The ERS-1 image contains a semi-circular feature that changes in
  contrast from bright to dark, consistent with model predictions
  for an anti-cyclonic eddy.  Aircraft SAR images collected over
  the same feature about 11 hours later show similar patterns.
  Furthermore, images collected with orthogonal look directions
  show a contrast reversal as predicted for this type of current
  field.  These images also reveal an additional fine structure
  which suggests the presence of internal waves near the boundary
  of the eddy.  It is hypothesized that these features may be
  associated with the changes in pycnocline depth that would be
  expected in the vicinity of such an eddy.

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry