A Climatology-Based Model for Long-Term Prediction of Radar Beam Refraction

The National Air Intelligence Center, WPAFB, OH, needs more accurate predictions of radar beam refraction. A new mode was developed for this thesis replacing the standard atmosphere approach with raytracing and climatology. Usually a microwave radio beam bends towards the earth with a radius of curvature greater than the earth's surface. However, seasonal and climatic variations influence the bending, and at times create temperature or moisture inversions that redirect the energy along the earth's surface leaving radio holes where there is no coverage. This model uses iterative raytracing to determine the most direct path from radar to target through the climatologically predicted refractive atmosphere. The height error is calculated by comparing the geographic path to the refracted path. Only vertical refractivity variation (including the effects of ducting) is taken into account. The model computed height errors at 17 locations worldwide for a target at 10,000 feet and 60 nautical miles that varied from 100 feet to 2260 feet compared to 804 feet predicted by standard atmosphere. The model traces to all targets when no ducting is modeled, to all targets outside the duct with surface ducting, and to some targets outside the duct with elevated ducting due to ducting ambiguities.