Browsing by Author "Kauristie, Kirsti"

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Auroral Imaging With Combined Suomi 100 Nanosatellite and Ground-Based Observations: A Case Study
(2023-05) Kallio, Esa; Harri, Ari Matti; Knuuttila, Olli; Jarvinen, Riku; Kauristie, Kirsti; Kestilä, Antti; Kivekäs, Jarmo; Koskimaa, Petri; Lukkari, Juha Matti; Partamies, Noora; Rynö, Jouni; Syrjäsuo, Mikko
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Auroras can be regarded as the most fascinating manifestation of space weather and they are continuously observed by ground-based and, nowadays more and more, also by space-based measurements. Investigations of auroras and geospace comprise the main research goals of the Suomi 100 nanosatellite, the first Finnish space research satellite, which has been measuring the Earth's ionosphere since its launch on 3 December 2018. In this work, we present a case study where the satellite's camera observations of an aurora over Northern Europe are combined with ground-based observations of the same event. The analyzed image is, to the authors' best knowledge, the first auroral image ever taken by a CubeSat. Our data analysis shows that a satellite vantage point provides complementary, novel information of such phenomena. The 3D auroral location reconstruction of the analyzed auroral event demonstrates how information from a 2D image can be used to provide location information of auroras under study. The location modeling also suggests that the Earth's limb direction, which was the case in the analyzed image, is an ideal direction to observe faint auroras. Although imaging on a small satellite has some large disadvantages compared with ground-based imaging (the camera cannot be repaired, a fast moving spinning satellite), the data analysis and modeling demonstrate how even a small 1-Unit (size: 10 × 10 × 10 cm) CubeSat and its camera, build using cheap commercial off-the-shelf components, can open new possibilities for auroral research, especially, when its measurements are combined with ground-based observations.
Numerical Ray Tracing of Medium and High Frequency Radio Waves in the Terrestrial Ionosphere
(2019-01-29) Fontell, Mathias
Perustieteiden korkeakoulu | Master's thesis
This thesis develops a numerical ray tracing program to study the propagation of medium and high frequency radio waves in the terrestrial ionosphere. Based on the cold plasma wave approximation and geometrical optics, a ray tracing program is developed in C++ to numerically solve the paths of radio waves transmitted as skywaves. The thesis presents the key properties of the terrestrial ionosphere as a medium for radio waves. We show how the Appleton-Hartree dispersion relation can be used with the Hamiltonian ray equations to obtain a solution to the radio ray path by adaptive numerical integration. Depending on the polarization of the radiating antenna, we present methods for evaluating the signal attenuation by magnetoionic splitting, ground reflections, and D-layer absorption. Moreover, we present a Monte Carlo method for estimating the geometric attenuation of skywaves. The performance of the developed ray tracing program is validated against theoretical and empirical results. We find that the computed predictions of the maximum usable frequency agree well with the predictions of commercial software, representing at most a difference of 8% between our ray tracer and the commercial program. Moreover, we ascertain that the developed ray tracer produces reversible ray paths, a property that is expected on the basis of first principles. Finally, the developed program is used to predict coverage maps of a high frequency receiver in orbit, demonstrating how ray tracing and ray reversibility can be utilized to deduce high frequency ground stations that are within reach of a satellite.
Radar – CubeSat Transionospheric HF Propagation Observations: Suomi 100 Satellite and EISCAT HF Facility
(2022-10) Kallio, Esa; Kero, Antti; Harri, Ari-Matti; Kestilä, Antti; Aikio, Anita; Fontell, Mathias; Järvinen, Riku; Kauristie, Kirsti; Knuuttila, Olli; Koskimaa, Petri; Loyala, Jauaries; Lukkari, Juha; Modabberian, Amin; Niittyniemi, Joonas; Rynö, Jouni; Vanhamäki, Heikki; Varberg, Erik
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Radio waves provide a useful diagnostic tool to investigate the properties of the ionosphere because the ionosphere affects the transmission and properties of High Frequency (HF) electromagnetic waves. We have conducted a transionospheric HF-propagation research campaign with a nanosatellite on a low-Earth polar orbit and the EISCAT HF transmitter facility in Tromsø, Norway, in December 2020. In the active measurement, the EISCAT HF facility transmitted sinusoidal 7.953 MHz signal which was received with the HEARER radio spectrometer onboard 1 Unit (size: 10 cm × 10 cm × 10 cm) Suomi 100 space weather nanosatellite. Data analysis showed that the EISCAT HF signal was detected with the satellite’s radio spectrometer when the satellite was the closest to the heater along its orbit. Part of the observed variations seen in the signal was identified to be related to the heater’s antenna pattern and to the transmitted pulse shapes. Other observed variations can be related to the spatial and temporal variations of the ionosphere and its different responses to the used transmission frequencies and to the transmitted O- and X-wave modes. Some trends in the observed signal may also be associated to changes in the properties of ionospheric plasma resulting from the heater’s electromagnetic wave energy. This paper is, to authors’ best knowledge, the first observation of this kind of "self-absorption" measured from the transionospheric signal path from a powerful radio source on the ground to the satellite-borne receiver.