John M. Goodman

Ionospheric effects on modern electronic systems

A basic overview of ionospheric phenomenology is provided. Some of the modern electronic systems of interest and the extent to which the ionosphere may place limits on design and operation are discussed. The effects of importance to electronic systems are defined, and the effects are discussed by frequency regime: the ELF ( >

A long‐term investigation of the HF communication channel over middle‐ and high‐latitude paths

A study of HF communication link and network availability has been carried out using frequency modulated continuous wave (FMCW) swept-frequency sounders operating in an oblique-incidence configuration. The sounder deployment enabled 28 middle- and high-latitude paths to be evaluated; the time period of the study was from December 1994 until the summer of 1996. Propagation conditions including ionospheric mode information, maximum observable frequencies, signal-to-noise ratios, and channel availabilities for digital data communication were derived and archived. The objective of the study was to ascertain the efficacy of HF data link communication for a proposed aeronautical-mobile service. Data were used to simulate the propagation environment which would be experienced in actual operation and to evaluate the value of path and frequency diversity in overcoming various propagation effects. It has been concluded that path and frequency diversity will lead to channel availabilities approaching nearly 100% and that a practical engineering solution was possible. These positive results are achievable if and only if dynamic frequency management methods are invoked. The paper outlines the nature of a real-time system, which is based upon a terrestrial FMCW swept-frequency sounder constellation and by which communication nowcasts and short-term forecasts are developed to drive a dynamic frequency management system.

Traveling ionospheric disturbances observed through use of a Thomson scatter technique employing Faraday rotation at 140 MHz

Abstract The Thomson scatter technique has been combined with Faraday rotation in order to deduce electron densities over the Naval Research Laboratorys Randle Cliff Radar facility. The Randle Cliff Radar frequency of ∼140 MHz has been shown to be approximately ideal for use of this hybrid technique at mid-latitudes. Electron density measurements made between ∼180 and ∼500 km during the daytime from November 1969 to May 1970 show both long (68 min) and short (20 min) period traveling ionospheric disturbances (TID); the average amplitude associated with the TID was found to be ∼4 per cent. It is suggested that the longer period TID may be useful in deducing certain atmospheric parameters such as neutral scale height or temperature.

New generation topside sounder

Having ionospheric electron density distributions as a function of height, latitude, longitude, and time under different conditions is essential for scientific, technical, and operational purposes. A satellite-based, swept-frequency, HF sounder can obtain electron density profiles on a global scale. We are developing a new generation HF sounder that employs recent developments in technology, electronics, and processing capabilities. It will provide global-scale electron density distributions, contours of fixed densities, maps of ƒoF2, hmax, etc. It will allow us to map irregularities, estimate anomalous propagation and conditions for ducting, determine angles of arrival, etc. It will also be able to perform various plasma diagnostics and, because of new flexibility, will be programmable from the ground to perform a variety of experiments in space. Need for such a system exists through the Department of Defense and several civilian agencies. Some of the novel features of the system include software-based design, direction of arrival estimation and synthetic aperture radar-type operation, onboard processing, and reconfigurable and flexible architecture with multimission capabilities.

Updated climatological model predictions of ionospheric and HF propagation parameters

The prediction performance of ionospheric conductivity and electron density (ICED), RADAR C, and Ionospheric Communications Analysis and Predictions Program (IONCAP) climatological ionospheric models is evaluated for different regions and sunspot number inputs. With conventional sunspot numbers, based on the observed solar 10.7-cm flux, ƒ0F2 prediction errors at Boulder for a particular month are no less than 18%. Use of the U.S. Air Force Global Weather Center (AFGWC) global sunspot number SSNE, extracted from ionosonde data for use with the ICED model, gives 15% errors. A dramatic improvement involves the use of single-station ionospheric data to update the driving parameters of an ionospheric model for near-real-time (NRT) predictions of ƒ0F2 and other ionospheric and HF circuit parameters. For middle latitudes the improvement extends out thousands of kilometers from the update point to points of comparable corrected geomagnetic latitude. At very large distances an update scheme which exploits a strong global dependence on geomagnetic activity shows promise. For the purpose of NRT predictions of the entire electron density profile the use of two distinct effective sunspot numbers for the bottomside, coupled with one or more model parameters for the topside, is suggested for model updates from a single station.

Some evidence of Es-layer effects upon 137 MHz radio waves

Abstract The occurrence of pronounced scintillation of radio waves transmitted from synchronous satellite Early Bird (1965-28A) appears to be correlated with the growth of the Es layer frequency ƒ 0 E s . The scintillation disturbances are usually short term but occasionally exist for as much as an hour. A number of the disturbances have well defined quasi-periodic edges although they generally exhibit a noisy spectrum.

Practical methods for highly reliable HF communications

Since 1993, TCI/BR investigators have been examining the potential of frequency and path diversity in solving many of the problems which have longed plagued HF communication systems and have hindered its effectiveness. While our results have application to voice communication, our primary motivation is directed toward the improvement in reliability for conveyance of digital data. Paths include polar cap, auroral zone, high-latitude trough, as well as mid-latitude channel environments. These paths have been selected to ascertain the relative correlation properties under both benign and pathological conditions, and the resultant data are being used to validate emerging real-time ionospheric and HF performance prediction models. These results have application for design and operation of highly reliable HFDL service for DoD applications in stressed environments and in various aeronautical-mobile and maritime applications. In this paper, we will outline the importance of path and frequency diversity toward the improvement in system availability. Emphasis will be given to results which have been obtained from an analysis of radio paths within the high latitude and arctic regions. These have been selected since the pathological behaviour exhibited by the relevant skywave channels provides us with an abundant opportunity to test our several design hypotheses based upon application of diversity. We have developed estimates of performance for an HF data link service based upon Chirpsounder records and HFDL modem specifications.

Communication availability enhancement of hybrid systems through exploitation of media diversity: evaluation of HF and satellite communication impairment mechanisms

Diversity schemes have been developed to enable HF systems to recover from media-specific disturbances, and fade margins are typically applied to ameliorate the effects of fading on satellite communication links. In this paper we describe a hybrid system concept comprised of an L-band Satcom and a terrestrial HF communication system. We examine the synergy which exists between these media in terms of composite communication connectivity, a synergy which may derive from an independence of failure mechanisms. In the analysis we make use of two climatological codes for estimating performance or impairment: WBMOD, a Satcom scintillation prediction code, and VOACAP, a well-known HF communication prediction model.

Global Considerations for Utilization of Real-Time Channel Evaluation Systems in HF Spectrum Management

Real-Time Channel Evaluation (RTCE) devices are coming into increased use in modern management of HF communications systems. The earliest techniques used in channel evaluation exploited vertical incidence pulse sounders (VIS) and these devices are still being used for some applications. An oblique incidence sounding technology has also been developed employing both pulse and chirp waveform approaches. There are a variety of RTCE devices which are identified in the paper but the major emphasis is placed on the OIS chirp sounder. Using this device as a canonical channel evaluator, the implications for global, theater, and local HF resource management may be addressed. As one might suspect, there are both advantages and disadvantages which may accrue from construction of a sounder network. Issues include: data applicability, data collection and dissemination, network size and cost, network ECM vulnerabilities, optimum network architecture, and system component reliabilities to name a few. These issues are outlined in the paper.