Summary
International Symposium on Antennas and Propagation
2010
Session Number:3TD4
Session:
Number:3TD4-2
Ground-to-Air Propagation in a Dense Jungle
Mauro S. Assis,
pp.-
Publication Date:2010/11/23
Online ISSN:2188-5079
Summary:
People engaged in a military or a scientific mission in a forest environment normally dispose of radio sets to be used for communication between then. In the case of a dense jungle, sometimes it happens that all group or part of it may become lost in this environment. It should be pointed out that even the GPS signal can suffer a very strong attenuation due to the vegetation and a precise localization of this group becomes unfeasible. In this context, the availability of radio sets is of paramount importance to carry out a successfully search and rescue operation. A similar situation is the case of an airplane crash in the jungle. In such scenario, the radio equipment to be localized must be capable to operate with a voice channel or emitting a help radio signal put in action by some automatic device. The unknown position of the radio station can be settled by air with the aid of a search equipment mounted in an airplane or helicopter, complemented by another equipment on the ground, inside the forest or outside of it in a vehicle on a road or in a boat along a river. The option to be considered depends on the access available in the region where the operation is being carried out.A crucial problem in the above scenario is the evaluation of the coverage area of the equipment to be localized. In a dense jungle, this coverage is limited by the high signal attenuation due to vegetation. This attenuation depends on the operating frequency and on the values of the electrical parameters of vegetation (electrical permittivity and conductivity). A study developed in the Brazilian Amazon region has shown that the optimum frequency to be used in operations inside the jungle is around 10 MHz [1,2]. On the other hand, the electrical characteristics of vegetation were estimated through an experimental procedure which involves the comparison of direct measurements of field strength decay versus distance with numerical values derived from a theoretical model. The best fit were achieved for εf = 1.2 (electrical permittivity) and σf = 0.2 mS/m (conductivity) [3]. The evaluation of signal attenuation when both radio stations are on the ground is available elsewhere [4,5]. However, results for ground-to-air propagation are scarce and not well documented in the technical literature. Based on a theory developed by Brekhovskikh [6], this problem is discussed in this paper. An acceptable agreement was observed when comparing theoretical results with experimental data measured in the Brazilian Amazon jungle.