Search

Personnel at the Naval Command, Control and Ocean Surveillance Center, RDT and E Division, and RP Consultants conducted a year-long study to measure and characterize auroral-E propagation. Personnel installed a 100-watt transmitter at the Arctic Submarine Laboratory at Cape Prince of Wales (67 N, 168 W) and a receiver at RP Consultants' facilities 900 kilometers away. Both sites used simple dipole antennas. The transmitter sent a slow morse R on a frequency of 25.545 megahertz (MHz). Only a very dense patch of ionization, typical of sporadic-E or auroral-E with foEs greater than 5 MHz, would sustain a sky-wave signal over this path. The solar sunspot number declined from 175 to less than 100 during the test period. Personnel recorded over 1400 auroral sporadic-mode observations whose durations spanned 1 minute to several hours. A strong diurnal dependence was noted. This document presents an initial characterization of auroral-E occurrences, noting time of day, season, and magnetic activity. It discusses some implications of auroral-E occurrence intensity. The data are also discussed with respect to the development of a new auroral-E expert system model.... Auroral-E propagation, Sporadic ionization, Auroral electrojet.

This technical document, actually a system design document or functional description document, covers the Disturbance Impact Assessment System (DIAS). This system is a computer software package designed to assess the effects of solar flares on HF radio communications. The document describes its software functions and their interrelationships. Specifically, the document (1) provides background information on the effects of high levels of solar activity on high-latitude HF missions, (2) outlines the architecture of DIAS, and (3) defines the product that DIAS provides to the user.... Propagation, Prophet, Propagation forecast, Solar disturbance, Expert systems.

In late 1980 questions arose concerning whether the ionosphere was sufficiently stable to allow precisely measured time of arrival of skywave signals to be used for geolocation in the high frequency (HF) band between 2 and 32 MHz. The chief limitation in the accuracy of this type of systems is the amount of uncertainty in the ionospheric height estimation and its temporal stability. Traditional ionospheric research resources did not address the issue in sufficient detail and time resolution to be of any assistance. In order to understand the exact nature of the ionospheric uncertainties and to quantify their extent, experimentation was proposed to sense the variation in the refraction height of the ionosphere as it relates to the time of arrival of the HF signal. The objective of this work was to determine the range of environmentally induced errors in a skywave Time Difference of Arrival (TDOA) measurement, thereby bounding the ultimate geolocation accuracy one could expect from this technique. The first experimental measurement system started operation in early 1981. This effort involved establishing a continuous absolute Time of Arrival (TOA) experiment over the one-hop midlatitude path between San Diego, California and Fort Collins, Colorado. The system is fully digital and stabilized with a cesium beam standard. This work was supplemented with vertical incidence sounder data at both ends of the path, a collateral Doppler sensing system, and coincident satellite solar data. A fully annotated database was prepared and is maintained by the Naval Ocean Systems Center Advanced Propagation Forecasting System (PROPHET).

Propagation in the LoVHF (30-100 MHz) frequency band possesses characteristics common to both HF (3-30 MHz) and HiVHF (100-300 MHz) propagation. It is this feature which makes this frequency band both interesting and complex. The primary interest of this report is the modes of propagation between surface- or near-surface-based transmitters and receivers. For a given range, the strength, geographical and temporal dependence, and likelihood of a particular mode of propagation will be discussed. In the last section, various existing models that could be used to describe the field strength and transmission loss in the LoVHF band are assessed. These models and the discussion of the various modes of propagation fall roughly into two groups: (i) those that affect ranges less than 500 km and (ii) those that affect ranges greater than 500 km.

PROPHET denotes a class of radio propagation forecast terminals which represent the culmination of an 11-year development effort at the Naval Ocean Systems Center (NOSC) under the SOLRAD satellite program. The system is unique in that it provides a real-time link between Navy operations personnel and a worldwide network of ground-based and satellite-borne solar-terrestrial environment monitors. This link is used to generate - via distributed data processing - electromagnetic system performance predictions in formats specially tailored to meet the operational requirements of the user. An initial implementation of PROPHET has provided - over a 3-year period - highly successful hf frequency/antenna management support to the Technical Control Facility of the Naval Communication Station at Stockton, CA. This executive summary provides a concise overview of the evolution, structure, function, and accomplishments of PROPHET, together with recommendations for ways in which the PROPHET technology can be applied to recognized operational requirements fo the Navy. Technical details are elaborated in volume II. (Author)

Within an 800-8000 km range, the original MINIMUF-3 reported in NOSC TR 186 will predict hf MUF within specified confidence limits. But the development of new applications involving very long transmission paths uncovered several bugs. Corrections are reported here that do not affect the original accuracy limits but do allow MINIMUF to be used out to the antipodal point. This document presents the most current model, called MINIMUF-3.5, describes the improvements, and presents a data set with which each user can check out his version of MINIMUF-3.5. (Author), See also Rept. no. NOSC-TR-186, AD-A052 052.

MINIMUF-3 is a semiempirical model for predicting the maximum usable frequency (MUF) for hf propagation. It was designed to allow simplified hf propagation predictions to be performed in a near-real-time mobile, tactical environment. An 80-statement BASIC language subroutine is presented which outputs MUF for arbitrary input values of receiver/transmission position, month, date, time (UT), and solar sunspot number. The program is compatible with existing and newly emerging generations of mini- and microprocessor-based computers. Results of extensive tests comparing MINIMUF-3 against hf oblique sounder data are also presented. The sounder data encompassed 196 path months (4704 test points) of observed MOFS from 23 different hf transmission paths. The overall rms residual error of MINIMUF-3 was 3.83 MHz. The results compared favorably with those obtained from large-scale hf prediction codes that were exercised against the same sounder data set. (Author)

The technique described will allow controllers to quickly determine (1) whether a short wave fade in progress will affect any of their hf circuits, (2) the degree to which each circuit is affected, (3) alternative frequencies, and (4) alternative traffic routes available. The only required input parameter is 1 - 8A X-ray flux. The computer program continuously displays the LOF over any number of preselected hf transmission paths in predictive, real-time, or historical mode. The technique was designed primarily for naval commands which control hf systems covering large geographical areas, such as Communication Area Management Sections at Navy Communications Stations and HF Direction Finding Net Control.

Development of a solar-disturbance forecasting system for reducing or circumventing degradation of performance in operational systems depends upon the ability to (1) describe the earth environment in terms of a transfer medium for the specific system and (2) assess and predict the effects of solar-radiation fluctuations upon the transfer medium and, hence, upon the system performance. A need exists for a wide range of solar X-ray, UV, and particle measurements with time resolution, spectral resolution, and dynamic range, so that solar emissions can be monitored in detail continusouly and in near real-time. The SOLRAD High Satellite System (SR XI A, B, C) offers the only sensor package capable of providing the necessary data inputs for a suitable solar/ionospheric disturbance forecasting system. (Author)