Ionospheric measurement using a linearly polarized tri-band small satellite beacon

Abstract

Radio waves propagating the ionosphere are subject to a number of unpredictable and corrupting effects, the most significant of which are phase path reduction, Faraday rotation, and scintillation. A method of measuring these effects is necessary in order to study and understand the solar-terrestrial connections, as well as to anticipate their impact on radio systems. However, limitations in current measurement solutions, most notably the lack of direct ionospheric Faraday rotation measurement capability, restricts the ability to characterize the ionosphere to a sufficient degree for applications such as the detection of coronal mass ejections. The rise in popularity of small satellites presents a new cost-effective opportunity to study and observe the ionosphere in detail, however the challenge of realizing a beacon within the constraints of a small satellite system must be overcome. In this paper, we introduce a measurement technique that builds on past multi-frequency beacons, incorporating the well established differential phase technique, as well as introducing a new differential polarization technique. We achieve this by employing linearly polarized beacon signals, which enables us to separate phase path reduction and Faraday rotation into a phase and polarization error respectively. The introduction of linear polarization overcomes a key limitations in current ionospheric measurement techniques: eliminating errors associated with indirect Faraday rotation measurement. The additional polarization data also enables absolute unambiguous measurement of both parameters with fewer and lower frequencies than conventional solutions, as well as without the need for precise satellite clock, phase biases and positioning data. These characteristics correspond with a reduction in the size, power and complexity of the satellite payload, and as a result, our technique better suited to small satellite applications. To validate the capability of measuring the ionosphere within the constraints of a small satellite package, we establish the influence of system noise, weak scattering, clock errors and antenna characteristics on the measurement technique. We then use this to inform a starting point for a CubeSat beacon and receiver design solution which achieves unambiguous and high-resolution measurement of ionospheric parameters with practicable system requirements and constraints. This starting point demonstrates that a resolution of 12mTECU and 0.03rad/m2 for the electron density and Faraday rotation estimates respectively, as well as useful scintillation measurements dominated by scintillation noise may be achieved utilizing a tri-band 3U CubeSat beacon with frequencies 144.2MHz, 432.6MHz, and 1297.8MHz, a transmitter power of no more than 4watts, and antenna requirements consistent with a dipole type antenna.