SPIRE GLOBAL'S OPERATIONAL GNSS-REFLECTOMETRY CONSTELLATION FOR EARTH SURFACE OBSERVATIONS

Spire Global designs, builds, and operates one of the largest satellite constellations in the world for Earth observations. Using a state-of-the-art GNSS receiver, the constellation is able to produce a variety of Earth observation products that include atmospheric profiles from radio occultation (RO) measurements, and Earth surface characteristics from reflected GNSS signals (GNSS-R). Since 2018, the receivers onboard Spire's GNSS-RO satellites were configured to additionally measure GNSS reflections at grazing angles (GA-GNSS-R), i.e., between 5 and 30 degrees elevation. Currently, over 20 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 has also launched four GNSS-R satellites that measure reflections near nadir (NN-GNSS-R) i.e. between 20 and 90 degrees elevation. These use deployable nadir-pointing antennas and process delay-Doppler maps (DDMs) 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 speed and mean-squared sope. Spire has been continuing to improve on the state-of-the-art to both observe more reflections and improve the quality of measurement. The grazing-angle GNSS-R has seen a 3.5x increase in the number of observations in 2022 through improvements to the payload including improved efficiency and multi-constellation grazing-angle observations. With the near-nadir GNSS-R constellation, Spire has been preparing for the next generation of receiver to launch in 2023, and improving the existing satellites by rolling out onboard digital beam-forming for increased antenna gain. We present the Spire Global operational grazing angle GNSS-R and near-nadir GNSS-R constellation status, developments in the data products and the new updates to the constellation for 2023. The Spire GNSS-R constellation is operationally generating observations that flow into NASA CSDA Programme and ESA EarthOnline.