Abstract
Urgency. The urgency is caused by the need to continuously monitor with radio instrumentation dynamic processes acting in the ionosphere, which arise due to variations in space weather, the impact of high-energy sources of natural and anthropogenic origin. To meet this challenge, V. N. Karazin National University and Harbin Engineering University specialists has developed a coherent multi-frequency multi-path radio system for obliquely probing the ionosphere. Purpose of Work. The paper illustrates the instrument capability for the study of dynamic processes arising in the ionosphere during a solar terminator, a moderate earthquake, a strong ionospheric storm, and in the cource of a partial solar eclipse. Techniques and Methodology. The system design is base on the software-defined radio (SDR) technology. The system is capable of receiving radio waves in the 10 kHz – 30 MHz band. The versatile computer software permits us to adjust the system for solving various problems. The number of the radio propagation paths and their orientation depends on the problem being solved. The premise upon which this radio system operation is based is measurements of the Doppler shift of the frequency. The autoregressive algorithm provides a 0.02 Hz root-mean-square Doppler line error and 7.5-s time resolution. Having the Doppler spectrum time dependencies for various radio paths archived, time series corresponding to various radio-wave modes undergo further processing. Results. As an example of successful instrument performance, dynamic processes operating in the course of a dusk terminator, the moderate (magnitude 5.9) earthquake on July 7, 2018, the strong ionospheric storm on August 26, 2018, and the partial (0.74 magnitude) solar eclipse over China on August 11, 2018 have been investigated. The ionospheric response to the impact of energy sources of various nature has been detected and investigated; it was accompanied by an increase in the number of rays, Doppler spectrum broadening, aperiodic and quasi-periodic variations in the Doppler shift of the frequency, generation of alternating sign variations in the electron density and wave disturbances having atmospheric gravity wave and infrasound parameters. Conclusions. The radio system located at the Harbin Engineering University campus successfully performs continuous radio monitoring of dynamic processes caused by various energy source in the ionosphere.
Highlights
The capabilities of probing the ionosphere with radio sounders at oblique incidence for solving the problems of radio wave propagation, ionospheric physics, and dynamic processes acting in the ionosphere are greater than the capabilities of digisondes operating at vertical incidence [1, 4, 7 – 22]
The multi-frequency coherent passive radar that has been developed at the Harbin Engineering University
remotely over different radio paths has shown a high efficiency of observing dynamic processes occurring in the ionosphere
Summary
The capabilities of probing the ionosphere with radio sounders at oblique incidence for solving the problems of radio wave propagation, ionospheric physics, and dynamic processes acting in the ionosphere are greater than the capabilities of digisondes operating at vertical incidence [1, 4, 7 – 22]. The purpose of this paper is to present a brief description of the ionospheric observations made at oblique incidence on several frequencies over multiple radio paths from the Harbin Engineering University (45.78 N, 126.68 E) where the passive Doppler radar is located [24 – 32]. The most dramatic signature of the disturbances due to the earthquake is the spectrum broadening toward negative shifts with a 50–116-min delay which depends on the orientation of the radio path Such a time delay suggests an approximately 0.3 km/s speed, and the atmospheric gravity waves generated by the earthquake as the cause of this effect
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