Speaker
Description
A 29 MHz frequency modulated continuous wave (FMCW) bi-static radar system that illuminates the ionosphere from a CubeSat in low earth orbit (LEO) has been developed. The radar transmitter uses a Linear Frequency Modulation (LFM) format that matches that of the Coastal Observation Radar (CODAR) system. The frequency of 29 MHz is chosen because radio propagation at that frequency is affected by the ionosphere, transmit antenna size is physically realizable, and the licencing at that frequency is in the Amateur-satellite service.
The globally distributed SDR based radar receivers are operated by radio Amateurs and citizen scientists to measure characteristics of the ionosphere. The SDR receivers run a GNU Radio flowgraph to measure the impulse response (multipath) and Doppler shifts of the radio propagation path from satellite to ground through the ionosphere. The system may be viewed as a bi-static radar with transmitter and receiver in different location. The measured data and metadata is uploaded by the citizen scientists to a central data repository operated by the project team and is made publicly available for analysis.
One of the main objectives of the project is science outreach, to motivate citizen scientists and radio Amateurs to learn about radar systems, ionospheric science, SDR, GNU Radio and LEO satellites, involving the public the in the mission of Skya’anaSat, the 3U CubeSat developed by the authors as a LEO signal source for this project, in the context of the CUBICS program funded by the Canadian Space Agency. While there are numerous papers in the literature describing FMCW radar using GNU Radio for a range of applications including observation of terrestrial CODAR signals, none exist on observation of signals originating from a LEO CubeSat. The GNU Radio flowgraphs developed for FMCW may be adapted for this project. A short-term goal is to develop robust GNU Radio CODAR Toolbox that yields results out-of-the-box.
Another objective is to provide a LEO signal source for observations using radio telescopes. The authors have access via an annual call for proposals to observing time on the Long Wavelength Array (LWA) based in New Mexico USA and have successfully made observations for the last five years. The LWA features a 256 element array of broadband cross-polarized inverted vee dipoles covering 10-88 MHz. Processing of LWA data can create an all-sky image of signals arriving at various azimuths and elevations and will provide direction-of-arrival information and antenna gain that is not practical for citizen scientists using simple dipole or Yagi antennas.
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