C. Watson, R. B. Langley, D. R. Themens, A. W. Yau, A. D. Howarth, and P. T. Jayachandran. Enhanced Polar Outflow Probe ionospheric radio occultation measurements at high latitudes: Receiver bias estimation and comparison with groundā€based observations. Radio Science, American Geophysical Union, volume 53, 2018 .