Ionospheric Propagation Modes Research Articles

Use of Hazard Function for Signal Detection on Ionograms

This letter considers a new method for sample detection of ionospheric propagation modes at the receiver output of a chirp ionosonde. The method is based on the use of the hazard function. Within the framework of the two-component mixture model, it is shown that the hazard function can be used to detect samples of the second component in the mixture when the corresponding fraction of samples in the total number is small. The implementation of the method is carried out using training sets. An average normalized hazard function is constructed for the training set not containing the signal. Normalization is carried out in such a way that the hazard function can be considered as a probability density function of a certain random variable. We used Pearson’s statistic to test the agreement between the average normalized hazard function of samples that do not contain the signal and an arbitrary normalized hazard function. The critical value of the statistic was determined using the Neyman–Pearson criterion. The effectiveness of the proposed method has been tested for the determination of the lowest and maximum observed frequencies of radio paths from oblique ionospheric sounding ionograms obtained in the Russian network of circumpolar radio paths. The method suggested in this letter can be used not only when processing ionograms but also for the detection of samples of signals of arbitrary nature against a background noise, provided that statistical signal-to-noise ratios are similar to those considered here.

A Long-range Ocean Radar for Ocean Surface Studies using Backscatter Via the Ionosphere

An HF Doppler radar, designed for use at long range via an ionospheric propagation mode, has been developed primarily for the determination of wave states over large ocean areas. The operating frequency is 21 �840. MHz, and the array is physically rotatable through a full 3600 of azimuth, thus allowing for great flexibility in the choice of target area. The experimental technique utilizes a well-known resonance interaction mechanism for electromagnetic waves backscattered from a moving sea wave surface to derive sea state parameters in the scattering region for input to oceanographic and meteorological synoptic data networks. An ultimate angular resolution of less than 10 of azimuth, coupled with high operational flexibility, suggest possible utilization of the aerial array for tracking and interrogating free-floating ocean buoys, tracking radio noise associated with tropical cyclones and investigating aspects of ionospheric dynamics.

Direction-finding observations on the 20 Mc/s transmissions from the artificial earth satellites

Some direction finding, and associated radio observations on the artificial earth satellites are described. It is shown that it should be possible to derive the elements of the local track from a single observational sequence on a nearby transit. Samples of several bearing transits are presented and discussed in relation to possible ionospheric propagation modes. Reference is made to the occurrence of irregularities in bearing, signal strength and Doppler records, which might yield data on the ionosphere if detailed orbit information becomes available.

The geometry of auroral communications

As early as 1939, radio amateurs found auroral ionization useful for communication purposes. Such ionization makes hf and vhf propagation possible over paths as great as several hundred kilometers when other more normal ionospheric propagation modes do not exist. The geometry of reflection is investigated for a variety of transmitter locations based upon the assumption of specular reflection from columnar ionization aligned with the earth's magnetic field lines. The results of the investigations outline the region of useful auroral ionization and the regions on the earth within which the auroral propagation is possible. The probability has been determined of obtaining propagation from a particular transmitter location to any receiver location within the region of propagation. These geometrical studies allow the communicator to predict the most useful transmitter and receiver locations in utilizing auroral ionization for communication purposes. The studies also may suggest methods of minimizing the effects of auroral propagation when it is considered a detrimental propagating mode, for example, when it results in undesirable multipath effects.

Long range meteoric echoes via F-layer reflections

This note reports HF observations of meteoric back-scatter echoes at ranges greatly exceeding radio line-of-sight. The observations were part of a program of measurements on backscatter using COZI equipment, Examples are given of observations at South Dartmouth, Massachusetts in 1949 on 16 mc and of more recent observations in 1954 on 12 and 16 mc using improved equipment. Short duration echoes are observed in advance at ranges shorter than those of the ground backscatter. No such meteoric echoes are observed when the ground backscatter disappears. The meteoric echo ranges move with time of day just as the range to the ground backscatter moves. A plausible explanation for the observed meteoric echo ranges exceeding 1,000 miles is that they are due to backscatter from the trail, ionospherically propagated to and fro via the F region, just as the ground backscatter. Other possible ionospheric propagation modes are discussed