Browsing by Author "Partamies, Noora"

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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.
Automatic segmentation and classification of seven-segment display digits on auroral images
(2016-07-21) Savolainen, Tuomas; Keith Whiter, Daniel; Partamies, Noora
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
In this paper we describe a new and fully automatic method for segmenting and classifying digits in seven-segment displays. The method is applied to a dataset consisting of about 7 million auroral all-sky images taken during the time period of 1973-1997 at camera stations centred around Sodankylä observatory in northern Finland. In each image there is a clock display for the date and time together with the reflection of the whole night sky through a spherical mirror. The digitised film images of the night sky contain valuable scientific information but are impractical to use without an automatic method for extracting the date-time from the display. We describe the implementation and the results of such a method in detail in this paper.
On the determination of ionospheric electron density profiles using multi-frequency riometry
(2022-01-27) McKay, Derek; Vierinen, Juha; Kero, Antti; Partamies, Noora
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Radio wave absorption in the ionosphere is a function of electron density, collision frequency, radio wave polarisation, magnetic field and radio wave frequency. Several studies have used multi-frequency measurements of cosmic radio noise absorption to determine electron density profiles. Using the framework of statistical inverse problems, we investigated if an electron density altitude profile can be determined by using multi-frequency, dual-polarisation measurements. It was found that the altitude profile cannot be uniquely determined from a "complete"measurement of radio wave absorption for all frequencies and two polarisation modes. This implies that accurate electron density profile measurements cannot be ascertained using multi-frequency riometer data alone and that the reconstruction requires a strong additional a priori assumption of the electron density profile, such as a parameterised model for the ionisation source. Nevertheless, the spectral index of the absorption could be used to determine if there is a significant component of hard precipitation that ionises the lower part of the D region, but it is not possible to infer the altitude distribution uniquely with this technique alone.