Fresnel scattering model for the specular echoes observed by VHF radar


  • K. S. Gage,

  • B. B. Balsley,

  • J. L. Green


In recent years several groups using VHF radars have reported highly anisotropic echoes originating from stable regions of the troposphere and stratosphere. The echoes are most intense looking vertically, and their occurrence is well correlated with regions of hydrostatic stability. Observations also show that the echoes are usually much stronger when observed with coarse spatial resolution. There is no commonly used scattering or reflection model that can account for these features. In this paper we present a new model to explain the enhanced vertical echoes. The model pertains to scattering from the half-wavelength Fourier component of horizontally coherent fine structure in the radio refractive index within a region of finite vertical extent. We refer to this echoing mechanism as ‘Fresnel scattering.’ The new model is applied to simulate the magnitude of VHF radar echoes by using radiosonde temperature soundings as input. Good agreement is found between these simulations and observations at the Sunset VHF radar in Colorado.