THE IMPACT OF REFLECTIONS FROM TREES’ TRUNKS ON SIGNAL FORMATION OF RADIO-WAVE DEVICES OF METER RANGE DETECTION IN THE WOODS

Abstract

Background. In the procedure of security of state facilities, the urgent task is to detect intruders in the wood. The advanced means of solving this problem is buried radio-wave detectors operating within VHF band. The aim of this work is to study the effect of side reflections at tree trunks on the signal formation in radio-wave detectors to assess the likely distortion of the intruder signals in the wood. Materials and methods. The article describes previously developed signal generation models of radio-wave detectors based on the well-known assumptions for the specified frequency range, ground parameters and distances. Results. Reflections of electromagnetic waves from tree trunks cause a change in the intruder’s signal in the wood compared with the signal generated by an intruder in the open space. Simulation of these processes shows that: the change in signal amplitude generated by the intruder in the wood is caused by the relative position of the tree trunks relative to each other and relative to the Fresnel zones of radio-wave detectors; maximum effect on the amplitude of the intruder signal is caused by trees located within the first Fresnel zone; the amplitude change of the intruder signal is maximum when the intruder moves near the tree trunk and can reach 10–20 % of its amplitude in open space; the signal amplitude of the intruder in the wood changes more when the ground is wet, but it is within its value when the ground is dry. Conclusions. When radio-wave detectors are located in the wood, one should consider that signal amplitude generated by an intruder can be reduced. The simplest way to compensate for its reduction is to reduce the distance between the transmitter and receiver of the radio-wave detectors.

Keywords

• scattered field of tree trunk
• intruder scattering field
• direct signal
• intruder signal