Initial Polarimetric Radio Occultation Results from Spire’s Nanosatellite Constellation

Spire Global has been operating three Polarimetric Radio Occultation (PRO) payloads since early 2023. They are the first nanosatellites to collect such datasets, following the initial demonstration from the secondary ROHP payload onboard the PAZ mission since 2018. The development of Spire’s novel payload effort has been supported by ESA through the InCubed project PROGRES.

In this presentation, we will show the first results of nine months of calibration and validation for Spire’s PRO-capable satellites. Nearly 2000 occultation events are processed daily from polarimetric observations of multi-GNSS signals. The differential phase shifts observed by the phase delays in the H and V polarizations are shown to match with precipitation events as determined by colocations with the IMERG product. Furthermore, combining the H and V signals together to reconstruct the RHCP signal results in a higher SNR and similar RO retrieval statistics when compared to the RO-only antenna onboard. This result suggests that measurements collected through Spire's PRO antenna are also suitable for the data assimilation of RO bending angle in operational Numerical Weather Prediction (NWP) models.

The goal of these datasets, which can uniquely sense precipitation events and icy particles from GNSS signals passing through the limb of the atmosphere, is to augment operational NWP models.