This paper presents a novel full-wave analysis of the radio waves that are excited from a dipole antenna located in the trunk layer and propagate inside a four-layered forest medium The dyadic Green's functions for the four-layered geometry are applied first to derive the integral expression of the electric fields The closed form of the electric fields is then obtained by using the quasi-static approximation, saddle-point technique, and branch-cut integrations in the complex plane and, hence, expressed in terms of direct waves, multiple reflected waves, and lateral waves Two kinds of images, ie, the quasi-dynamic and complex images, are considered in the integration in the complex plane Among those waves excited by a dipole antenna in the four-layered medium, it is shown theoretically and numerically that the lateral wave along the upper-side air-canopy interface plays a role of dominant modes The propagation mechanism of other lateral waves due to the air-canopy, canopy-trunk, and trunk-ground interfaces is also discussed and analyzed so as to gain an insight into the wave characteristics Transmission losses of the lateral waves are calculated numerically

Radio wave propagation along mixed paths through a four-layered model of rain forest: an analytic approach

Propagation of electromagnetic waves in forest environments is examined in which both the transmitting and receiving points are located in the trunk layer of a four-layered anisotropic forest model. This propagation model considers the forest as a horizontally stratified, anisotropic media of canopy and trunk, bounded by ground below and air above. The electromagnetic fields are obtained using dyadic Green's functions in their eigenfunction expansion forms for an anisotropic four-layered geometry. Analytical results are found for the fields, which consist primarily of three wave modes: a direct wave, multiply reflected waves, and lateral waves. These field constituents are compared, and their domains of preponderance are calculated; it is found that the lateral wave plays a major role in communication at large distances. Radio losses for typical forest are calculated to illustrate numerical application of the forest model.

Analysis of radiowave propagation in a four-layered anisotropic forest environment

Thesis (Ph.D.) -- University of Adelaide, School of Electrical and Electronic Engineering, 2009

/pdf/radio-propagation-in-fire-environments-5u8zbvjfly.pdf

Radio propagation in fire environments.

In this paper, rainfall efiect on the VHF radio-wave propagation in a tropical forest is further studied in details. Theoretical study and experimental investigations are performed with the help of a four-layered model for forested environment. It is found that the lateral wave traveling along the air-canopy interface, the direct waves, and the ground re∞ected waves are the main modes for VHF radio-wave propagation in forest. The rainfall can afiect these propagating waves to difierent extents. Especially, due to the increase in the dielectric permittivity of the wet canopy layer by rain water, the time of arrival of the direct wave traveling through the canopy layer can be delayed signiflcantly. Finally, the dielectric permittivity for the wet canopy layer under difierent rain events is evaluated empirically.

/pdf/further-study-of-rainfall-effect-on-vhf-forested-radio-wave-1iqez5qq4i.pdf

Further study of rainfall effect on vhf forested radio-wave propagation with four- layered model

A four-layered forest geometry with two anisotropic slabs representing canopy and trunk is used for the investigation of wave characteristics in forest environment. Propagation of radio waves is examined in which the transmitter is embedded inside the forest, while the receiving point is located either inside the forest or above the vegetation. Dyadic Green's functions in their eigenfunction expansion forms for planarly layered anisotropic media are applied to analyze this problem. The analytical close forms of these electric fields are then obtained by using the saddle point techniques, and branch cut integrations in the complex plane and, hence, expressed in terms of quasidirect wave, multiply reflected waves, and lateral waves. Propagation mechanisms of these waves are studied and radio losses in a typical forest are calculated numerically.

Wave mode and path characteristics in a four-layered anisotropic forest environment

The paper describes a stochastic radiowave propagation model useful for assessing the effects of forests and other vegetation on communications signals in the UHF band. The stochastic electromagnetic theory employed as the basis of this model considers the forest as a planar, stratified, anisotropic, discrete, random medium, bounded above by air and below by ground, of randomly positioned and oriented canonical scatterers representing the principal forest constituents (tree trunks are represented as infinitely long, parallel, circular, dielectric cylinders; branches as short ones; and leaves as flat, circular, dielectric discs). A physically appealing representation for the mean (coherent) field component of the propagating radio wave has been obtained by recognising that the ensemble of discrete scatterers can be replaced by an equivalent continuous medium described by an effective dyadic permittivity e. The associated electromagnetic boundary-value problem is solved to identify the principal contributions to the mean field: the direct wave, the reflected wave and the lateral wave. Because the equivalent continuous medium characterised by the effective dyadic permittivity e is linear, Fourier-transform techniques have been employed to generalise the model so that it accommodates arbitrarily modulated waveforms.

Stochastic model for pulsed radio transmission through stratified forests

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Stochastic model for pulsed radio transmission through stratified forests