Simulating radar propagation through atmospheric turbulence using the Tropospheric ElectroMagnetic Parabolic Equation Routine (TEMPER)

The Tropospheric Electromagnetic Parabolic Equation Routine (TEMPER) being developed by the Fleet Systems Department at the Applied Physics Laboratory has proven to be a useful tool in predicting low-altitude radar propagation. A marching procedure is used to step the field through what has been assumed to be a deterministic spatially varying index of refraction profile. In an actual environment, small-scale random fluctuations from atmospheric turbulence are superimposed on the deterministic profile. In this report a method for coupling random refractivity fluctuations into TEMPER is proposed and tested numerically. Three-dimensional spectral models from the atmospheric literature are used to derive the one-dimensional transverse spectra of refractivity necessary for parabolic simulations. Realizations consistent with the spectra are generated using filtered white noise. Propagation studies are conducted for the canonical problem of a plane wave transmitted through homogeneous isotropic turbulence. Good agreement is observed between the numerical results and existing theory for the second moment of the scattered field. However, the agreement is less good for predicting the random fluctuations in the log-amplitude of the field as three-dimensional effects become significant. Methods for simulating inhomogeneous boundary layer turbulence are considered. The limits of spectral modeling for simulating turbulence are discussed.