Observations and Modeling of Traveling Ionospheric Disturbance Signatures From an Australian Network of Oblique Angle‐of‐Arrival Sounders

• Published in: Radio science Vol. 53; no. 9; pp. 1089 - 1107
• Main Authors: Heitmann, Andrew J., Cervera, Manuel A., Gardiner‐Garden, Robert S., Holdsworth, David A., MacKinnon, Andrew D., Reid, Iain M., Ward, Bruce D.
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 01-09-2018
• Subjects: angle‐of‐arrival; Antenna arrays; Atmospheric models; Delay; Doppler; Electron density; Elevation; HF direction finding; Incidence; Ionograms; Ionosondes; Ionosphere; ionospheric modeling; Ionospheric propagation; Ionospheric sounding; oblique incidence ionosonde; Performance enhancement; Radar signatures; Radio waves; Ray tracing; Scattering functions; Signal processing; traveling ionospheric disturbance; Traveling ionospheric disturbances
• ISSN: 0048-6604; 1944-799X
• DOI: 10.1029/2018RS006613

A network of oblique angle‐of‐arrival (AoA) ionosondes was installed as part of the Elevation‐scanned Oblique Incidence Sounder Experiment (ELOISE) in September 2015. The ELOISE experimental campaign was designed to study the spatial and temporal structure of ionospheric variability at midlatitudes, of which traveling ionospheric disturbances are a key component. The new AoA sounder makes use of Defence Science and Technology Group's direct‐digital high‐frequency transmitter and receiver technology, to enable multichannel collection of both ionograms and channel scattering functions (Doppler spectra) on a common 2‐D array. In this paper, the array design and onboard signal processing for the AoA sounder is described, along with a sample of results showing typical disturbance signatures across the delay, Doppler frequency, bearing, and elevation measurements. Realistic parameterized models of electron density perturbations, along with geometric ray tracing, were used to synthesize the effects of medium‐ to large‐scale traveling ionospheric disturbances on the sounder observables and aid in interpreting the measured signatures.
Plain Language Summary
The ionosphere is an outer charged layer of the Earth's atmosphere that is used by technologies such as over‐the‐horizon radar to “bounce” (refract) high‐frequency radio waves out to very long distances beyond the horizon. However, as a propagation medium, the ionosphere is far from uniform, and to improve the performance of such radars, it is necessary to better understand the nature and sources of variability that affect high‐frequency propagation. One of the aims of the Elevation‐scanned Oblique Incidence Sounder Experiment (ELOISE), conducted by Defence Science and Technology Group in September 2015, was to study the wave‐like perturbations known as traveling ionospheric disturbances by receiving a network of low‐power ionospheric sounder (or ionosonde) transmissions on two new antenna arrays. These were designed to measure path delay, angle‐of‐arrival and Doppler shifts simultaneously on multiple paths. This paper describes the ELOISE array and its signal processing and provides examples of typical observations. It is shown that the characteristic signatures of traveling ionospheric disturbances in the measurements, combined with realistic synthetic models, can provide information about the structure and behavior of such ionospheric disturbances in space and time.
Key Points
Two interferometric receiving arrays have been used to observe a network of oblique ionospheric propagation paths from 900 to 2,700 km
Angle‐of‐arrival and Doppler measurements show the characteristic signatures of midlatitude traveling ionospheric disturbances
Synthetic disturbance models, combined with 3‐D ray tracing, have been used to classify and parameterize the observed signatures