Full-wave computation of characteristics of VHF radio link over random and nonstationary irregular terrain

Previously we described a method, based on a parabolic equation algorithm, for the computation of the impulse response of stationary deterministic channels. We focus now on random and nonstationary situations, extending our former approach to give efficient predictions when the propagation environment is partially undetermined and/or fluctuating with time. In the case of a radio link over a random irregular terrain, the mean terrain profile is supposed to be known, but it remains an indetermination/error because of the imperfections of the height measurements and the presence of vegetation and man-made structures. For a complete statistical characterization, the whole process used in the deterministic case has to be repeated for a certain set of possible implementations of the channel (Monte Carlo drawing). In particular, the mean impulse response may differ noticeably from the impulse response corresponding to the mean terrain. We apply a similar approach to the modeling of a nonstationary environment, i.e. a link affected by wind-induced vegetation motion. Results are encouraging and are compatible with most of the features obtained during previous experimental work. The top of the canopy is considered as a random surface whose variations of height with time and range were the superposition of a "rapid" stationary oscillation with amplitude randomly distributed with range (motion of leaves), and a sinusoidal progressive surface wave (undulation of tops of trees). We have been able to obtain time and Doppler characteristics of the channel.