Frequency effects in the radar return from turbulent, weakly ionizedmissile wakes.

An analysis is performed to determine the frequency content in the return signals resulting from monochromatic, plane-wave illumination of weakly ionized turbulent wakes. The frequency analysis is accomplished using generalized power spectra, and the expressions generated are shown to involve the space-time correlation of the turbulent fluctuations in electron density. A model is postulated for this correlation which amounts to a generalization of an expression originally due to Kovasznay. This model involves the mean-square fluctuation intensities of both velocity and electron density, as well as the mean velocity distribution. Utilizing simplified relations for the estimation of the required fluctuation intensities, the spectral theory is exercised in an application to a typical numerically generated, turbulent, ionized wake. The effects of variations in both parameter values and fluctuationmodel forms are illustrated by spectral density plots for a number of stations along the wake. The influence of velocity fluctuation intensity is shown to be dominant in the determination of received-signal spectral width. Nomenclature light speed, vacuum electric field incident electric field scattered electric field electron charge current intensity turbulence scale electron mass electron number density mean-square turbulent fluctuation in ne unit vector in direction from scatterer to observer far-field approximation to N radius, cylindrical classical electron radius local wake radius distance from scatterer to observer spatial autocorrelation function temporal autocorrelation function space-time correlation function of electron-dens ity fluctuations in vehicle-fixed coordinates contribution, per unit wake length to power spec