I. V. Dushko, D.N.Ivlev, V. A. Odnosevtsev, I. Ya. Orlov

The aim of this paper is the research of relative level of re-reflected by underlying terrain components of radar signal reflected from target. Three-component model of radar signal propagation from a target to radar system is offered in the article. According to this model a signal received by radar system can be presented as the sum of three components: direct ray propagating along the line-of-sight, quasi-specular returned ray and the sum of rays scattered by underlying terrain. The third component can be modeled as a random signal. Mathematical and algorithmic description of the model is given. The results of computer simulation of target-to-radar signal propagation are given and analyzed. Simulation has been carried out for 1500 MHz signal frequency, two different target-s motion paths (for static position of radar system), two types of underlying terrains (water and earth) and two height values of radar system above earth surface. At the simulation stage results in the form of target-s elevation dependences listed below have been obtained: a) power of the ray propagating along the line-of-sight (direct ray) b) power of ray quasi-specular reflected from underlying terrain c) power of noise signal formed by the sum of rays scattered by underlying terrain (scattered signal) d) power of coherently summed signals of direct and quasi-specular returned rays e) power ratio of direct and quasi-specular returned rays f) power ratio of direct ray and scattered signal Simulation was carried out both without taking into account the antenna pattern, and in view of sharp directional antenna. Radio channel simulation results show that quasi-specular returned ray can be ignored under conditions of terrestrial underlying surface if glancing angle exceeds several degrees. In this situation signal-to-noise ratio which depends on the signal scattered by underlying terrain is quite enough in all the range of target-s elevation to high-quality target-s signal sensing even without taking into account directional characteristics of antenna and is weakly depends on the height of radar-s position. Under conditions of water underlying terrain sensing of radio-locating signal reflected from target can be very difficult due to high power of noise component and quasi-specular ray that leads to low signal-to-noise ratio and to deep fast fading of received signal at small values of elevation. Taking into account sharp radar-s receiving antenna pattern signal-to-noise ratio under conditions of water underlying terrain becomes acceptable for high-quality signal sensing for elevation values that exceeds width of antenna pattern in elevation plane.