A comprehensive review of radio wave attenuation in forest environments is presented in this paper. The classic analytical methods of propagation loss modeling and prediction are described flrst. This provides information on the physical processes that the radio waves undergo while propagating through a forest. The focus of this paper is on the review and summary of the experimental work done in this area and the development of empirical propagation loss prediction models. The propagation loss variation due to external factors such as antenna height-gain, depolarization, humidity efiect etc. are examined and discussed individually. In view of current research work done in this area, some possible future work is proposed to improve the performance of radio links in forest environment.

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Study of propagation loss prediction in forest environment

This paper presents a new methodology to model the near- ground short-range propagation loss in forested areas at the VHF and the UHF band The path loss modeling is performed by an integration of the foliage induced efiect and the efiect from the radio- wave re∞ection/re∞ections The analysis shows that the re∞ection from the dense tree canopy is important for short-range propagation at the VHF band and therefore, cannot be ignored When taking into consideration the contribution from the possible tree-canopy re∞ection, the modeled path loss is reduced by more than 15dB in the VHF band A good agreement of the modeled path loss with the measured loss in tropical forested areas is achieved

Path Loss Modeling for Near-Ground VHF Radio-Wave Propagation through Forests with Tree-Canopy Reflection Effect

This paper presents mobile-to-mobile (M-to-M) channel measurements and models at 185 GHz in dense-scattering suburban areas Three test scenarios were considered for different transmitter (Tx) and receiver (Rx) antenna placements Scenario 1: inside-vehicle-to-inside-vehicle (IV2IV), where both Tx and Rx antennas were placed inside the test vehicles; Scenario 2: inside-vehicle-to-walk (IV2W), where the Tx antenna was placed inside the vehicle and the Rx antenna was inside the pocket or next to the face of the tester; and Scenario 3: walk-to-walk (W2W), where the Tx and Rx were moving at walking speeds, the Tx antenna was placed on a test cart, and the Rx was inside the pocket or next to the face of the tester To mimic more typical M-to-M channels in practice, eight sub-scenarios were configured under the availability of the line-of-sight (LoS) between the Tx and Rx Detailed channel models are proposed for path loss, shadowing, small scale, and multi-scale fading based on the collected measurements The level crossing rate (LCR) and average fading duration (AFD) are studied from the measurements and compared with the theoretical expressions

Mobile-to-Mobile Channel Measurements at 1.85 GHz in Suburban Environments

Impulse ultrawideband (UWB) communication promises a number of benefits for use in wireless sensor networks, particularly in forest environments, where it has the potential to provide robust operation, along with the ability to combine communications with precision position location. In this paper, we present measurement results and empirical models for UWB signal propagation in a forest environment. Path-loss measurements were performed using a 620-ps duration UWB pulse with a frequency range of 830-4200 MHz. More than 22 000 measurements were recorded in 165 locations in four diverse forest environments in Virginia and Maryland, USA. Transmitters and receivers were separated by distances that range from 4 m to 50 m. Large-scale path loss was most closely modeled by log-distance propagation, with path-loss exponents ranging from 2.5 to 3.8. Small-scale fading analysis indicated that UWB signals experience Rician fading, with K-factors in the range of 10-16 dB. K-factors were found to depend on forest type, with the medium-density forest providing the greatest number of multipath components and highest overall K-factor. Multipath component analysis demonstrated that a forest is a fairly rich multipath environment; however, in most cases, approximately 90% of the available energy was contained within the strongest 3-15 multipath components. Postprocessing analysis divided the UWB pulse into three frequency subbands and demonstrated that model parameters also had frequency dependence. These measurements and models should aid in the development of future UWB outdoor sensor networks.

Characterization of Low-Antenna Ultrawideband Propagation in a Forest Environment

1. We describe an automated radio telemetry system (ARTS) designed for estimating the location of 0.50 g butterflies which was constructed with commercially available materials. Previously described systems were not designed to estimate fine‐scale locations of large insects within approximately 200 m2 study areas. 2. The ARTS consists of four receiving stations. Each receiving station has four 3‐element, directional Yagi antennae (separated by 60) connected to an automated receiver that records detected power sequentially from each antenna. To develop and evaluate the ARTS performance, four receiving stations were installed in the corners of 4 and 6.25‐ha square fields with varying heights of vegetative cover. The location of a 0.22 g transmitter was estimated with a statistical method implementing both distance‐and angle‐power relationships. Calibrated model parameters were based on power detected from transmitters at known locations. Using independently collected data, model performance was evaluated based on estimated locations of a georeferenced stationary transmitter, a moving transmitter with a known georeferenced path and a transmitter attached to a monarch butterfly Danaus plexippus. Estimated locations were calculated as frequently as every 5 s, which is at least 12 times greater than the sampling frequency previously reported for tracking insects. 3. When sufficient power data were received, the median estimated locations of a transmitter attached to an investigator's hat were <16 m from the true location. The median effective radius of the>95% confidence ellipse was 18.3 m for stationary targets and 15.9 m for a moving transmitter. Greater error in location estimation was expected when the transmitter was attached to a monarch butterfly due to interference from vegetation and variability in antenna orientation and transmitter height. As such, the median distance between the estimated and true locations was 72 m. After applying a correction for the effect of vegetation, median location error was reduced by 12 m. 4. While our ARTS has likely reached the limit of current technology, the system is still a substantial methodological advancement for locating butterflies. Our efforts should provide a benchmark as technology improves.

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1372&context=nrem_pubs

Locating large insects using automated VHF radio telemetry with a multi-antennae array

In 1997 and 1998, measurements were made of radio wave attenuation through a cottonwood plantation at the University of Illinois at Urbana-Champaign, on a number of frequencies between 27 and 411 MHz. Based on these measurements, an empirical formula that describes radio wave attenuation was developed.

G.W. Swenson

Papers

Radio wave propagation through woods