  Wind is a critical component of the Earth system and has unmistakable impacts
on everyday life. The CYGNSS satellite mission improves observational coverage
of ocean winds via a fleet of eight micro-satellites that use reflected GNSS
signals to infer surface wind speed. We present analyses characterizing
variability in wind speed measurements among the eight CYGNSS satellites and
between antennas. In particular, we use a carefully constructed Gaussian
process model that leverages comparisons between CYGNSS and Jason-3 during a
one-year period from September 2019 to September 2020. The CYGNSS sensors
exhibit a range of biases, most of them between -1.0 m/s and +0.2 m/s with
respect to Jason-3, indicating that some CYGNSS sensors are biased with respect
to one another and with respect to Jason-3. The biases between the starboard
and port antennas within a CYGNSS satellite are smaller. Our results are
consistent with, yet sharper than, a more traditional paired comparison
analysis. We also explore the possibility that the bias depends on wind speed,
finding some evidence that CYGNSS satellites have positive biases with respect
to Jason-3 at low wind speeds. However, we argue that there are subtle issues
associated with estimating wind speed-dependent biases, so additional careful
statistical modeling and analysis is warranted.
