D. R. Siddle

Transhorizon radiowave propagation due to evaporation ducting: the effect of tropospheric weather conditions on VHF and UHF radio paths over the sea

A detailed description of evaporation ducts and their relevance to radiowave propagation over the sea has been presented. The constantly changing weather conditions over the sea mean that marine and coastal environments, in particular, are prone to these unusual tropospheric phenomena that facilitate radio waves to have higher signal strengths and to travel longer distances than expected. Therefore, the influence of evaporation ducts on over-sea radiowave propagation needs to be thoroughly investigated. Research in this area will have implications for maritime communication systems used in coastal cellular telephone networks, commercial shipping, naval radar operations and sea-rescue.

Near real‐time input to a propagation model for nowcasting of HF communications with aircraft on polar routes

There is a need for improved techniques for nowcasting and forecasting (over several hours) HF propagation at northerly latitudes to support airlines operating over the increasingly popular trans-polar routes. In this paper the assimilation of real-time measurements into a propagation model developed by the authors is described, including ionosonde measurements and total electron content (TEC) measurements to define the main parameters of the ionosphere. The effects of D region absorption in the polar cap and auroral regions are integrated with the model through satellite measurements of the flux of energetic solar protons (>1 MeV) and the X-ray flux in the 0.1–0.8 nm band, and ground-based magnetometer measurements which form the Kp and Dst indices of geomagnetic activity. The model incorporates various features (e.g., convecting patches of enhanced plasma density) of the polar ionosphere that are, in particular, responsible for off-great circle propagation and lead to propagation at times and frequencies not expected from on-great circle propagation alone. The model development is supported by the collection of HF propagation measurements over several paths within the polar cap, crossing the auroral oval, and along the midlatitude trough.

Long‐term statistics related to evaporation duct propagation of 2 GHz radio waves in the English Channel

[1] This paper presents long‐term statistics additional to those previously published pertaining to evaporation duct propagation of UHF radio waves in the British Channel Islands, with particular focus on a completely over‐sea 50 km transhorizon path. The importance of the evaporation duct as an anomalous propagation mechanism in marine and coastal regions is highlighted. In particular, the influence of various atmospheric parameters on the performance of a popular operational evaporation duct model is examined. The strengths and weaknesses of this model are evaluated under specific atmospheric conditions. The relationship between the continually varying evaporation duct height and transmitter‐receiver antenna geometries is analyzed, and a range of statistics related to the implications of this relationship on the received signal strength is presented. The various issues under investigation are of direct relevance in the planning of long‐range, over‐sea radio systems operating in the UHF band, and have implications for the radio regulatory work carried out by organizations such as the International Telecommunication Union. Citation: Gunashekar, S. D., E. M. Warrington, and D. R. Siddle (2010), Long‐term statistics related to evaporation duct propagation of 2 GHz radio waves in the English Channel, Radio Sci., 45, RS6010, doi:10.1029/2009RS004339.

Important aspects of transhorizon propagation at 2 GHz over the English Channel

Three 2 GHz radio paths have been established in the British Channel Islands to study the characteristics of long-range UHF propagation over the sea. Enhanced signal strengths (ESS) have been observed on all three radio links, predominantly in the late afternoon and evening periods in the spring and summer months. Relevant over-sea propagation mechanisms (e.g. low-lying evaporation ducts and higher-level ducting structures) have been identified and suitably modelled. The evaporation duct appears to be the primary propagation mechanism during most periods of normal reception. However, our analysis suggests that specifically during periods of signal strength enhancement, higher-level ducting structures become more dominant. In this paper, various statistical data related to tropospheric ducting in the region have been presented to confirm these observations.

Transhorizon propagation over the sea: Observations and predictions

Measurements of signal strength are reported for a study of UHF propagation on transhorizon sea paths in the British Channel Islands. Enhancements of up to 30 dB from the mean are seen for periods of hours or days, especially in the summer, and are present for up to 12% of the time overall. The probability distribution of received power is shown for the three paths and various antenna heights., and is compared with predictions of signal strength using ITU-R Recommendation P1546. Most notably, the median observed signal exceeds the median prediction by about 10 ¿ 15 dB. The upper decile, however, is in reasonable agreement.

An X-band radio channel model for propagation through the solar corona

This is a conference paper that is being expanded to a full journal paper. Numerical data for the figures are included in the supplementary information.

Developments in an HF nowcasting model for trans-polar airline routes

HF communications can be difficult in the polar regions since they are strongly influenced by space weather events. Airline communications within the polar regions rely on HF communications and improved nowcasting and forecasting techniques in support of this are now required. Previous work has demonstrated that ray tracing through a realistic, historical ionosphere provides signal coverage in good agreement with measurements. This paper presents an approach to providing a real-time ionospheric model by assimilating TEC measurements and validates it against observations from ionosondes.

Near real-time input to an HF propagation model for nowcasting of HF communications with aircraft on polar routes

The authors have previously reported on the development of an HF propagation model for signals reflected from the northerly regions of the ionosphere, and its validation by comparison with measurements made over a number of paths within the polar cap, crossing the auroral oval, and along the mid-latitude trough. The model incorporates various features (e.g. convecting patches of enhanced plasma density) of the polar ionosphere that are, in particular, responsible for off-great circle propagation and can lead to propagation at times and frequencies not expected from on-great circle propagation alone. Currently, the model drivers include ionosonde measurements and geomagnetic data from a period of several days spanning the time of interest. We have previously only examined the propagation effects on a historical basis, and have achieved good agreement between measurements and simulations.