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Prelaunch Performance of the 118.75 GHZ Polarcube 3U Cubesat Temperature Sounding Radiometer

The low cost PolarCube 3U CubeSat supports a 118.75 GHz imaging spectrometer for temperature profiling of the troposphere and surface temperature. It is a demonstrator for a constellation of LEO passive microwave imaging and sounding satellites at V and G bands using 3U/6U CubeSats. Such a constellation of ~40 satellites for weather forecasting will provide data at high spatial and temporal resolution to observe rapidly evolving mesoscale weather. The satellite payload is an eight channel, double sideband passive microwave temperature sounder with cross-track scanning and will provide 17.3 km surface resolution from a 450 km orbit. It's antenna system consists of a gold-plated offset paraboloidal reflector scanning at 1 Hz and a 3D printed corrugated feed with a 17.28° waveguide transition. This paper provides an overview of the radiometer including procedures used to determine optimum feed horn/reflector dimensions, phase center and antenna efficiencies. A brief description of the design and functionality of the eight channel intermediate frequency module is also provided. Initial performance results obtained from airborne measurements over Antarctica on the NASA DC-8 in November 2016 indicate a well-functioning radiometer and scanning antenna subsystem. The measured radiometer sensitivity varies from 1.3 to 2.6 K across the eight channels for an integration time of 4.096 ms. Gain stability of the various channels with ambient temperature variations were also measured.