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Development, implementation and testing of algorithms for measurements of electromagnetic signals detected onboard a stratospheric balloon above thunderstorms
Amrich, Samuel ; Santolík, Ondřej (advisor) ; Kašpar, Petr (referee)
In this work, we focus on the application of machine learning techniques to study radio recordings of lightning discharges. Our goal was to develop an algorithm that could autonomously detect and classify different types of lightning discharges, as well as their groups or developmental stages. To this end, we tested various methods of classical ma- chine learning as well as deep neural networks. All of these models were trained itera- tively on archival data. The results of our work show that it is possible to effectively use machine learning methods for detection and classification purposes, with the aim of deploying them on board the STRATELEC stratospheric balloon project. In the future, our findings should be deployed on board the stratospheric balloon and could be used to improve understanding of the processes involved in creating lightning discharges in a thundercloud. 1
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Nonlinear processes in space plasmas and their effects on the generation and propagation of electromagnetic waves
Hanzelka, Miroslav ; Santolík, Ondřej (advisor) ; Hellinger, Petr (referee) ; Rycroft, Michael J. (referee)
Nonlinear interactions of charged particles and large-amplitude waves have a signif- icant impact on magnetospheric dynamics. Here we focus on the cyclotron resonant interaction between energetic electrons and the discrete, whistler-mode chorus emissions in the Earth's outer radiation belt. The subject is introduced by an extensive review of whistler-mode dispersion properties, resonant electron trajectories and nonlinear wave- growth theories. We then present a new semi-empirical model of rising-tone chorus emis- sions with a fine subpacket structure. The model is then used in test-particle simulations to investigate nonlinear perturbations in hot electron distributions. Based on changes in electron fluxes, we estimate the resolution of spacecraft particle detectors required to detect the predicted perturbations. The test-particle method is further used to sim- ulate atmospheric precipitation of electrons caused by interaction with a single chorus wavepacket, and the result is put into connection with microbursts and pulsating auro- ras. We also detected a violation of the strong diffusion limit by the cyclotron resonant interaction, resulting in loss cone overfilling. 1
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Analysis of propagation of "lion roar" emissions using the data of the Cluster spacecraft
Krupař, Vratislav ; Santolík, Ondřej (advisor) ; Souček, Jan (referee)
The main task of this thesis was a statistical study of lion roar wave emissions in the Earth's magnetosheath. Large data set obtained from the Cluster spacecraft has been used. We have studied a frequency distribution, a wave power distribution and a spatial distribution. We have investigated propagation characteristics using advanced methods applied on multi-components measurement. We have confirmed the narrow-band structure of lion roars. We have compared observed and estimated (from the cold plasma theory) time lags between spacecraft during short separations.
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Stereoscopic Observations of Solar Radio Emissions by the S/WavesInstrument onboard the STEREO Spacecraft
Krupař, Vratislav ; Santolík, Ondřej (advisor) ; Krucker, Samuel (referee) ; Wimmer-Schweingruber, Robert F. (referee)
This PhD thesis is primarily dedicated to a study of type III radio bursts observed by the S/Waves instrument onboard Solar TErrestrial RElations Observatory (STEREO). These emissions are produced by beams of suprathermal electrons escaping the corona along open magnetic field lines during increased solar activity. As fast electrons propagate in the interplanetary (IP) medium, Langmuir waves are generated at the local electron plasma frequency fpe by a bump-on-tail instability and can be afterwards converted by a non-linear process into radio emissions at fpe and/or 2fpe: type III radio bursts. We have developed a goniopolarimetric (GP, also referred to as direction-finding) inversion using the Singular Value Decomposition (SVD) technique for electric measurements on three non-orthogonal antennas. It allows us to retrieve both wave vector directions and polarization properties of incident waves. We have also investigated the influence of extended sources (as a typical feature of type III radio bursts) on measured spectral matrices. We have found an empirical relation between apparent source sizes and spectral matrices decomposed by SVD. Abovementioned techniques have been extensively tested on data obtained by the High Frequency Receiver (HFR, a part of S/Waves). We have performed statistical analysis of a...
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Analysis of wave-particle interactions in space plasmas
Černý, Miroslav ; Santolík, Ondřej (advisor) ; Souček, Jan (referee)
This work deals with the linear analysis of plasma waves, especially with the methods of solution of a hot plasma dispersion relation. There are cited some results achieved in the space plasma research and mapped current numerical methods of their analysis. Besides, this work introduces a new numeric procedure, computer code PDRS (Plasma Dispersion Relation Solver), which allows finding solution of a dispersion function of a cold or hot plasma with general distribution function. It also demonstrates the usage of the PDRS methods on real examples of waves in space plasma based on the spacecraft Cluster measurement.
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