Recent Developments from Spire's GNSS Radio Occultation and Reflectometry Constellation

Spire Global designs, builds, and operates one of the largest satellite constellations in the world for Earth observations. Using a state-of-the-art, science-grade GNSS receiver, the constellation is able to produce a variety of Earth observation products that include neutral atmospheric profiles and ionospheric estimates from radio occultation (RO) measurements, and Earth surface characteristics from near-nadir and grazing angle reflected GNSS (GNSS-R) signals.

The majority of Spire’s satellites carrying a GNSS receiver are equipped with Earth limb-facing antennas that are primarily intended to collect RO signals for weather forecasting and atmospheric climate applications. Spire’s GNSS-RO constellation has been the world’s largest source of RO measurements for the past several years and has demonstrated the capability of producing over 20000 high-quality, RO profiles per day in near-real-time for operational weather forecasting. Ionospheric estimates of total electron content and scintillation are also routinely derived from dual-frequency GNSS measurements and are available with low enough latency to be valuable for space weather applications. The receivers onboard Spire’s GNSS-RO satellites are also configured to additionally measure GNSS reflections at grazing angles, i.e., between 5 and 30 degrees elevation, which has applications for sea ice extent, classification and precise altimetry. Finally, Spire has also launched several conventional GNSS-R satellites into orbit. Each of Spire’s conventional GNSS-R satellites uses deployable nadir-pointing antennas to produce delay-Doppler maps of reflection power. This is corrected to reflectivity using the onboard calibration and then utilized to derive products such as soil moisture and ocean wind speeds.

Spire has also more recently launched the first three of its satellites capable of collecting polarimetric RO (PRO) data. These satellites have demonstrated the collection of over 2000 PRO profiles daily, about 10 times the amount of data available through the PAZ mission. 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 bending angle measurements suitable for the data assimilation in operational Numerical Weather Prediction (NWP) models.

In this presentation, we will cover the current status and capabilities of Spire’s constellation of GNSS receivers as described above while also looking ahead toward the future.