Uncertainty of GNSS Radio Occultation in the Lower Troposphere: An Updated Analysis Through Multi-Center, Multi-Mission Comparisons

In the past decade, there has been tremendous growth in the field of GNSS-RO, with the launch of the COSMIC-2 constellation and Sentinel-6 MF, which carry the advanced NASA/JPL TriG receivers, and the proliferation of GNSS-RO data from commercially available small satellites that are capable of tracking GNSS signals from all major global GNSS constellations. At the same time, the unique value of GNSS-RO in vertically resolving the thermodynamical structures of the planetary boundary layer (PBL) has been further recognized and exploited, generating global PBL height products that were heretofore not possible. Nevertheless, the uncertainty of GNSS-RO in the lower troposphere and PBL remains insufficiently characterized. In this study, we are motivated by the highly successful characterizations of GNSS-RO retrievals in the upper troposphere and lower stratosphere through multi-center, multi-mission comparisons and utilize a similar approach to quantify the uncertainty of GNSS-RO bending angle, refractivity, temperature, and water vapor profiles. The availability of GNSS-RO data from very different receivers with widely different signal-to-noise ratios should provide new insights on such characterizations. The results of this study will produce a more definitive uncertainty estimate of GNSS-RO retrievals in the lower troposphere and PBL that will help inform current and future efforts in combining GNSS-RO with other measurements.