The aim of this document is to identify the required steps towards full exploitation of the GNSS polarimetric radio occultation data and technique, and to share it with potential interested agencies and related scientific communities. GNSS Polarimetric Radio Occultation (PRO) is a new technique to sense vertical atmospheric profiles of both thermodynamic variables (temperature, pressure, moisture) and hydrometeors, especially in intense precipitation and convection events. The proof-of-concept demonstrator is orbiting aboard the PAZ satellite and acquiring data since 2018. Since then, other commercial satellites have orbited GNSS PRO payloads (Spire Global and PlanetiQ Low Earth Orbiters). Despite the uniqueness of this technique, its data are not fully exploited yet. In part, this is due to the novelty and non-conventional aspects of the technique. Five potential applications have been identified thus far: Diagnosis Tool for NWP and their Microphysics parameterizations; Data Assimilation in NWP Models; Applications for Climate Models; Characterization of Frozen Hydrometeors; and Applications to Other Datasets. The document briefly analyzes what we know and what we do not know about GNSS PRO, and what we need to learn (studies), develop (software, tools) or acquire (data) to foster the exploitation of the GNSS PRO signals. The study concludes with the prioritized list of key aspects.

Contributors.-- Scope of this document.-- Executive Summary.-- 1. Background. 1.1 GNSS Polarimetric RO in a nutshell.-- 1.2 GNSS PRO demonstration misión.-- 1.3 Mandate of the 2nd PAZ-Polarimetric Radio Occultations User Workshop.-- 2. What we know and we do not know about GNSS PRO.-- 2.1 Facts.—Resolution.-- Response from the media.-- 2.2 Envisaged Applications.-- 2.3 Uncertain aspects.-- Open Questions.-- 3. Steps forward.-- 3.1 Key elements of the Roadmap.-- 3.2 Prioritization of pending elements.-- 4. Timeline.3-- References

Working Group Conclusions and Recommendations.

Collaborative effort.

Peer reviewed