GROUND PARAMETER INFORMATION FOR PROPAGATION MODELING

The relative success of various simplified ground impedance models at fitting data obtained from direct and indirect measurements is reviewed. A new two-parameter approximation for the normal surface impedance of a nonhard-backed layer structure is introduced. A two-parameter model of this form is shown to have wide success in fitting recent ground impedance and excess attenuation data obtained by a variety of techniques. Further evidence is produced of the unreliability that would be associated with extrapolation of fits based on the single-parameter semiempirical model widely used at present outside the frequency range of the fitted data. By refitting classical ground impedance data and tabulating resulting parameters along with those obtained more recently, a menu of ground types, best-fit models, associated parameter values and frequency ranges of fits has been compiled.