Predicting and visualizing changes in the index of refraction for radio frequency signals in the troposphere

Abstract:

Birnbaum and Kryder (1951) produced one of the seminal papers on radio frequency refraction in the atmosphere related it to temperature, water content, and permeability of air. Smith and Weintraub (1953) extended and refined this work to note limited effect of water vapor on the refractive index at radio frequencies in the microwave region, thus making the pertinent factors atmospheric pressure and absolute potential temperature. Reuger (2002) undertook a review of previous work noting the widespread use of refraction at GPS frequencies in the range of roughly 1-2 GHz for geodetic efforts especially pertaining to nuisance variable of wet and dry delay in postprocessing carrier-phase GPS solutions. We will again review the pertinent literature and demonstrate a post-processing tool that analyzes output from the Weather Research and Forecasting model (National Center for Atmospheric Research, Mesoscale and Microscale Modeling Division), displaying potential ducting tracks in 3D, accounting for surface, near-surface and elevated tropospheric ducts. Using standard forecasts that present the requisite predictive variables as output, predictions of atmospheric ducting can reasonably be predicted by demonstrating differences in the index of radio frequency refractivity in the atmosphere.