stochastic modeling of tropospheric wave propagation

F1: Wave Propagation and Remote Sensing

STOCHASTIC MODELING OF TROPOSPHERIC WAVE PROPAGATION Funda Akleman1 & Levent Sevgi1,2 1

ITU Electronics and Communication Engineering Department, 80626 Maslak / Istanbul, TURKEY Fax: (90) 212 – 285 3679 Email: [email protected] 2 Raytheon Canada Limited 400 Phillip Street, Waterloo, Ontario, N2J 4K6 CANADA Summary

Tropospheric radiowave propagation has gained increasing attention because of widespread usage of different radar and communication systems, such as air defence, ground environment, surface search, air-borne and ship-borne applications. Deterministic modeling of tropospheric radiowave propagation mostly depends on high quality, high-resolution refractivity profiles, especially in the first few kilometers above the earth’s surface. Analytical modeling of these problems are extremely difficult because of their complexities and only approximate solutions[1] have been found until now. Although they are approximate, the physical insight gained from these solutions help to understand wave propagation phenomena in complex surroundings and permit interpretation of results obtained with purely numerical techniques[2]. Among the others, Split-step Parabolic Equation (SSPE) and Geometric Optics (GO) are two well-known methods which have been successfully applied to trace the footprints of wave propagation along the earth’s surface for various refractivity profiles including surface ducting[3], elevated ducting, surface-to-elevated-ducting[4] and guiding-to-antiguiding transitions[5]. The aim of this work is to focus on the stochastic nature of tropospheric radiowave propagation. The statistical variation of radio refractivity N, or modified refractivity M and their vertical gradients are introduced in both SSPE and GO techniques to account for the random variations in radio wave propagation. Available measurement data will be processed and the statistics of vertical refractivity gradient will be obtained. Using these statistics, various vertical refractivity profiles will be produced. Then, these synthetically produced data will be used to model the stochastic nature of the troposphere above the earth’s surface. After the introduction of the statistical vertical refractivity gradient into both SSPE and GO methods Monte Carlo simulations will be performed to obtain signal strength variations at different source and observation locations. And finally, the effects of random variations in refractivity profiles on tropospheric radiowave propagation for different cases, such as surface ducting, elevated ducting including critical transitions (duct-toelevated duct, guiding-to-antiguiding), will be discussed. [1] L. B. Felsen & L. Sevgi, "Adiabatic and Intrinsic Modes for Wave Propagation in Guiding Environments with Longitudinal and Transverse Variations: Formulation and Canonical Test", IEEE Transactions on Antennas and Propagat. Vol.39 No.8, pp.1130-1136, Aug. 1991 [2] L. Sevgi & L. B. Felsen, "A new Algorithm for Ground Wave Propagation Based on a Hybrid Ray-Mode Approach", Int. J. of Numerical Modeling, Vol.11, No 2, pp.87-103, March 1998 [3] L. Sevgi "Split Step Parabolic Equation Solutions in Surface Duct-to-Elevated Duct Transition", Turkish J. of Physics, Volume 19, No 3, pp. 541-551, March 1995 [4] O. Ercan & L. Sevgi, "The PE Solution of Natural Waveguides in Atmosphere: Ducts and Elevated Ducts", MELECON'94, Proc. of Mediterranean Electrotechnical Conf., pp. 394-397, April 12-14 1994 Antalya, Turkey [5] S. Paker & L. Sevgi "Split Step Parabolic equation Analysis of Perfectly Conducting Convex-Concave Boundary", Proc. of PIERS'96, Progresses in Electromagnetic Research Symposium, V.1, pp. 149 (abstract), July 8-12 1996, Innsbruck, Austria