Fast, S.A., G.S. Young, J.N. Bode, and K. Pelman, 2000

A three-dimensional matching method for tropospheric features

Radio Science, 35, 1065-1073

Abstract

In order for high fidelity radio wave propagation models to make accurate predictions, a correct model of the refractivity is required. To this end several methods have been developed to match refractivity profile structures between multiple range dependent profiles. There is broad agree-ment that using refractivity to match features dismisses relevant information that should be used. The method presented here takes a different approach. When the parabolic equation meth-ods are used to calculate propagation loss, the refractivity is only required at each range step. Hence any method which can correctly predict refractivity at the range step is appropriate. Pre-vious methods match features for a given vertical cut of the atmosphere, thus introducing sam-pling errors and ignoring off planar effects. Here we match features in three dimensions using the virtual potential temperature, a conserved quantity derived from temperature, pressure, and specific humidity. The variables used to compute refractivity are then interpolated in this matched coordinate system using splines. This results in a correct mapping of features over a region which resolves sam-pling issues thus replacing refractivity with a smooth function in three dimensions. Therefore as a parabolic equation steps in range the refractivity is derived from the matched gridded data. This paradigm eliminates the burden of refractivity interpolation/extrapolation from the propa-gation prediction software. Examples of matched atmospheres are presented along with propa-gation predictions based upon the matched atmosphere.