Radar detection of missile plumes embedded in elevated atmospheric ducts

An elevated atmospheric duct results when the refractive index profile of the atmosphere increases then decreases with altitude. Propagation of electromagnetic waves close to the horizontal is similar to propagation in a parallel plate waveguide, effectively increasing detection range. The concept of employing an elevated radar centered in an atmospheric duct for the early detection of ballistic missile launches is investigated. Early detection of either the missile hardbody or the plume is sufficient to cue a ground based radar of the threat missile vicinity. Two methods are used to mathematically model atmospheric ducting-a split-step parabolic equation method and a geometrical optics method. Two different ducts are modeled-a high graded index duct and a low graded index duct. A ducting version of the radar range equation is developed incorporating all of the bistatic energy backscattered in the duct from the target. A simple plume scattering model is developed to predict bistatic RCS. The plume is modeled as a cylindrical overdense plasma surrounded by an underdense plasma. At 300 km range, power requirements for detection are shown to be three orders of magnitude lower with ducting present