English
norskBlar i forfatter "Kvammen, Andreas"
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The 3‐D Distribution of Artificial Aurora Induced by HF Radio Waves in the Ionosphere
(Journal article; Tidsskriftartikkel; Peer reviewed, 2019-03-21)We present 3‐D excitation rate estimates of artificial aurora in the ionospheric F layer, induced by high‐frequency radio waves from the European Incoherent Scatter heating facility. Simultaneous imaging of the artificial aurora was done with four separate Auroral Large Imaging System stations, permitting tomography‐like 3‐D auroral reconstruction of the enhanced atomic oxygen emissions at 6,300, ... -
Auroral classification ergonomics and the implications for machine learning
(Journal article; Tidsskriftartikkel; Peer reviewed, 2020-07-09)The machine-learning research community has focused greatly on bias in algorithms and have identified different manifestations of it. Bias in training samples is recognised as a potential source of prejudice in machine learning. It can be introduced by the human experts who define the training sets. As machine-learning techniques are being applied to auroral classification, it is important to identify ... -
Auroral Image Classification With Deep Neural Networks
(Journal article; Tidsskriftartikkel; Peer reviewed, 2020-10-05)Results from a study of automatic aurora classification using machine learning techniques are presented. The aurora is the manifestation of physical phenomena in the ionosphere‐magnetosphere environment. Automatic classification of <i>millions</i> of auroral images from the Arctic and Antarctic is therefore an attractive tool for developing auroral statistics and for supporting scientists to study ... -
Auroral Image Processing Techniques - Machine Learning Classification and Multi-Viewpoint Analysis
(Doctoral thesis; Doktorgradsavhandling, 2021-09-30)Every year, millions of scientific images are acquired in order to study the auroral phenomena. The accumulated data contain a vast amount of untapped information that can be used in auroral science. Yet, auroral research has traditionally been focused on case studies, where one or a few auroral events have been investigated and explained in detail. Consequently, theories have often been developed ... -
Authenticating the presence of a relativistic massive black hole binary in OJ 287 using its general relativity centenary flare: Improved orbital parameters
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-10-05)Results from regular monitoring of relativistic compact binaries like PSR 1913+16 are consistent with the dominant (quadrupole) order emission of gravitational waves (GWs). We show that observations associated with the binary black hole (BBH) central engine of blazar OJ 287 demand the inclusion of gravitational radiation reaction effects beyond the quadrupolar order. It turns out that even the effects ... -
K2 Campaign 5 observations of pulsating subdwarf B stars: Binaries and super-Nyquist frequencies
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-12-05)We report the discovery of three pulsating subdwarf B stars in binary systems observed with the <i>Kepler</i> space telescope during Campaign 5 of K2. EPIC 211696659 (SDSS J083603.98+155216.4) is a g-mode pulsator with a white dwarf companion and a binary period of 3.16 d. EPICs 211823779 (SDSS J082003.35+173914.2) and 211938328 (LB 378) are both p-mode pulsators with main-sequence F companions. The ... -
Lumikot: Fast auroral transients during the growth phase of substorms
(Journal article; Tidsskriftartikkel; Peer reviewed, 2019-06-25)The development of a magnetospheric substorm may be classified into three phases: growth, expansion, and recovery. The growth phase is important as it includes processes that lead to the expansion. In a recent growth-phase study, a type of fast discrete auroral transient phenomena -- referred to as Lumikot -- were observed. The Lumikot are several kilometers across and move in the high-energy ... -
Machine Learning Detection of Dust Impact Signals Observed by The Solar Orbiter
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022-08-11)This article present results from automatic detection of dust impact signals observed by the Solar Orbiter – Radio and Plasma Waves instrument.<p> <p>A sharp and characteristic electric field signal is observed by the Radio and Plasma Waves instrument when a dust particle impact the spacecraft at high velocity. In this way, ∼5–20 dust impacts are daily detected as the Solar Orbiter travels through ... -
Modeling Solar Orbiter dust detection rates in the inner heliosphere as a Poisson process
(Journal article; Tidsskriftartikkel; Peer reviewed, 2023-02-20)Context. Solar Orbiter provides dust detection capability in the inner heliosphere, but estimating physical properties of detected dust from the collected data is far from straightforward.<p> <p>Aims. First, a physical model for dust collection considering a Poisson process is formulated. Second, it is shown that dust on hyperbolic orbits is responsible for the majority of dust detections with ... -
The volume distribution of artificial aurora induced by HF radio waves in the ionosphere
(Master thesis; Mastergradsoppgave, 2016-08-15)This thesis presents three-dimensional modelling of artificial aurora in the ionospheric F layer, induced by high frequency (HF) O-mode radio waves from the EISCAT heating facility. Understanding how HF radio waves produces enhanced emission in the ionosphere has been one of the one of the major motivations for conducting heating experiments during the last decades. A key element for understanding ...
