Vestnik КRAUNC. Fiz.-Mat. Nauki. 2025. vol. 53. no. 4. P. 59 – 74. ISSN 2079-6641

INFORMATION AND COMPUTATIONAL TECHNOLOGY
https://doi.org/10.26117/2079-6641-2025-53-4-59-74
Research Article
Full text in Russian
MSC 68T10

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Recognizing a Group of Whistlers in VLF Radio Signals

E. A. Luttseva^{\ast}¹, G. M. Vodinchar¹²

¹Kamchatka State Technical University,683003, Klyuchevskaya st., 35, Petropavlovsk-Kamchatsky, Russia
²Institute of Cosmophysical Research and Radio Wave Propagation FEB RAS, 684034, Mirnaya st., 7, Paratunka, Kamchatka, Russia

Abstract. This paper presents a comprehensive approach to solving the problem of automatic recognition of groups of whistling atmospherics (whistlers) in the time-frequency spectra (spectrograms) of VLF radio signals. Such radio signals are generated by atmospheric electrical discharges passing through the magnetospheric waveguide and serve as natural markers of the Earth’s magnetosphere state. Object of study: spectrograms of VLF radio signals containing whistling atmospherics. Subject of study: algorithms for the automatic recognition and identification of groups of whistling atmospherics on time-frequency spectrograms. The proposed method involves a multi-stage algorithm for processing the source signal. The first stage involves signal filtering, which consists of two parts: modified median filtering and selection of significant samples. Next, a transition to a new coordinate system is performed, which allows for the transformation and “straightening”of the curvilinear patterns of whistlers. This transformation significantly simplifies subsequent analysis. The next stage is the recognition of a single whistler or multiple whistlers in
the signal fragment under consideration (this stage was addressed by the authors in previous work). The final stage is the search for groups of whistlers whose straightened patterns intersect at a single point on the time axis. For testing the final stage, signal fragments of two types were generated: an ideal group consisting of two straight lines (whistlers) that converge at a single point; two groups of straight lines (whistlers) approximating real-world whistler propagation conditions (by adding Gaussian noise and reducing the intensity of the second signal in the group). The described algorithm automates the process of identifying whistler groups, which enhances the objectivity and speed of analysis compared to visual methods.

Key words: whistlers, whistler group, pattern recognition, VLF radiation.

Received: 05.11.2025; Revised: 16.11.2025; Accepted: 23.11.2025; First online: 24.11.2025

For citation. Luttseva E. A., Vodinchar G.M. Recognizing a group of whistlers in VLF radio signals. Vestnik KRAUNC. Fiz.-mat. nauki. 2025, 53: 4, 59-74. EDN: SUEDVS. https://doi.org/10.26117/2079-6641-2025-53-4-59-74.

Funding. The work was carried out within the framework of the research project of the GBT of the FSBEI HE “Kamchatka State Technical University” (state registration number 124022500267-1) and the State Assignment of IKIР FEB RAS (reg. No. NIOKTR 124012300245-2).

Competing interests. There are no conflicts of interest regarding authorship and publication.

Contribution and Responsibility. All authors contributed to this article. Authors are solely responsible for providing the final version of the article in print. The final version of the manuscript was approved by all authors.

^{\ast}Correspondence: E-mail: luttsevaea@gmail.com

The content is published under the terms of the Creative Commons Attribution 4.0 International License

© Luttseva E. A., Vodinchar G.M., 2025

© Institute of Cosmophysical Research and Radio Wave Propagation, 2025 (original layout, design, compilation)

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Information about the authors

Luttseva Ekaterina Aleksandrovna – Senior Lecturer, Control Systems Department, Kamchatka State Technical University, Petropavlovsk-Kamchatsky, Russia, ORCID 0009-0003-6552-805X.

Vodinchar Gleb Mikhailovich – PhD (Phys & Math), Docent, Leading Researcher, Laboratory of Physical Process Modeling, Institute of Cosmophysical Research and Radio Wave Propagation FEB RAS, Paratunka, Russia; Associate Professor, Control Systems Department, Kamchatka State
Technical University, Petropavlovsk-Kamchatsky, Russia, ORCID 0000-0002-5516-1931.

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