Recent Updates to Spire’s GNSS Radio Occultation and Reflectometry Constellation for Operational Weather Data

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 currently produces RO profiles 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. More recently in 2023, Spire launched the first three of its polarimetric RO capable satellites, which provide measurements sensitive to precipitation along with traditional RO-observing variables.

The Spire constellation also continuously monitors valuable geophysical variables of the Earth’s surface through GNSS-R measurements. The receivers onboard Spire’s numerous GNSS-RO satellites are configured to measure GNSS reflections at grazing angles, i.e., between 5 and 30 degrees elevation. Spire satellites continuously measure grazing angle GNSS-R events in areas of high-coherence, i.e., calm waters and glaciated surfaces, which are used to create products of sea ice extent, classification and precise altimetry. Spire also operates conventional GNSS-R satellites in orbit that 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’s Earth observation data have been evaluated by NOAA, NASA, NRL, USAF, ESA, EUMETSAT, ECMWF, and the UK Met Office, all with positive results. Since 2020, Spire has been an active participant of the NOAA Commercial Radio Occultation Data Program by supplying near-real-time data for further processing and assimilation into operational weather forecast models. Over the past year, it has also participated in NOAA’s Commercial Space Weather Data Pilot Program by supplying low-latency data with the potential to improve space weather forecasting. Due to its large satellite constellation and technological maturity, Spire has supplied GNSS data to NOAA at unmatched consistency on a daily basis throughout all of its delivery orders. On the European-side, Spire has also supplied near-real-time RO data to EUMETSAT over the past several years with similar success. Finally, Spire’s GNSS-based Earth observation products have been made available for research users and applications primarily through participation in NASA’s Commercial Smallsat Data Acquisition Program (CSDA).

In this presentation, we will describe the current status and capabilities of Spire’s Earth observation constellation and the derived GNSS-RO and -R products being operationally delivered to downstream users.