Morphology of the scattering target: Fresnel and turbulent mechanisms

Further studies of VHF radar signals from the troposphere and stratosphere revealed not only scattering from isotropic turbulence at scales of half the radar wavelength but also partial or Fresnel reflection or scattering from horizontally stratified temperature discontinuities. Proof for this observation was given by the large spatial and temporal coherence of radar signals. Thin structures, particularly in the stratosphere, may be persistent over some ten seconds, which is longer than the coherence time of 3 m scale turbulence in the stratosphere. The vertical thickness of the structures was estimated to be much thinner than 150 m. Observations over a longer time period indicate that these fine scale structures or sheets are clumped together forming patches or ensembles of mostly downward sloping structures.