Polarimetric Spectrometer Receivers for Remote Sensing of Ionospheric Currents

The solar storms create ionospheric currents around the poles of the Earth. These currents cause variations in the local magnetic fields that give rise to the Zeeman frequency splitting of the oxygen absorption peak at 118.75 GHz. We developed polarimetric spectrometer receivers that measure the magnitude and polarization of the black body radiation from these oxygen absorption peaks allowing remote sensing of the ionospheric currents that cause them. The receivers have an average noise temperature of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$370 \mathrm{K}(\text{NF}=3.6 \text{dB})$</tex> and their low power, mass and volume allowed accommodation in the 0.2 mx <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0.2 \mathrm{m} \times 0.1 \mathrm{m}$</tex> space on a 6 U CubeSat. These are the lowest noise polarimetric receivers reported at these frequencies.