Integrated propagation modeling method for homeland security applications

Abstract

In this dissertation, an integrated simulation code has been developed to model and characterize the radio wave propagation in these challenging environments. One exemplary environment considered is a hilly area (a realistic radar site) facing the ocean and with slopes and rough/irregular terrain where the radar antennas are located. The integrated method involves three numerical techniques: the Finite-Difference Time-Domain (FDTD) method, the Parabolic Equation (PE) method, and the ray-tracing (RT) method. The advantages and disadvantages of these methods are examined to identify their best application domain. First, the FDTD method is found suitable to simulate propagation in small regions with possible fine structures present such as the hill with antennas. The FDTD method can accurately characterize the effect of slope and roughness on radio propagation which in turn impacts the phases of the radar array elements and need to be considered in the beam-forming design of a radar or communication system. Second, the PE method is employed for simulating propagation over the flat ocean, land/ocean transition and irregular terrain. This region is defined to be right above the ocean surface and has a small height satisfying the paraxial propagation requirement. For launching PE calculation, the FDTD results on the boundary of its small region near the source are used to serve as the initial field distribution needed by the PE method. This approach provides more accurate PE calculations because the scattered field from the hill is taken into account in the FDTD initial field. Ray-tracing (RT) method is also employed as a third method to calculate field in the atmospheric area above the PE and the FDTD calculations regions. The optimal computation domain of each of these regions is investigated through several numerical comparisons of their respective modeled propagation behavior at the boundaries between and in overlapping regions. In these comparisons both speed and accuracy of propagation factor were considered to optimize the performance of the integrated code. Finally, the integrated method is implemented with the optimal computation domain size for each of these methods. The integrated method employing the PE, the RT, and the FDTD, each in its own computation domain of applicability, has broad application domain in radar and communication application and shows better accuracy than any of the individual methods. The integrated method can handle both vertical and horizontal polarizations. Several experimental measurements were carried out in a land/ocean transition area to verify the simulation of the integrated propagation modeling code and excellent agreement of the field strength was observed.