Radar—CubeSat Transionospheric HF Propagation Observations: Suomi 100 Satellite and EISCAT HF Facility.

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 High frEquency rAdio spectRomEteR (HEARER) onboard 1 Unit (size: 10 × 10 × 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. Key Points: Active radar‐satellite transionospheric measurements in the high frequency (HF) range with a CubeSat‐size satellite have been performedA radio spectrometer onboard the Suomi 100 CubeSat detected a clear signal transmitted by the EISCAT HF heaterThe properties of ionospheric plasma were found to be affected by the energy of the transmitted heater signal [ABSTRACT FROM AUTHOR]