Proceedings Article | 20 September 2020
KEYWORDS: Satellites, Satellite navigation systems, Global Positioning System, Earth's atmosphere, Atmospheric monitoring, Atmospheric sciences, Atmospheric scintillation, Environmental sensing, Climatology, Scintillation
Spire Global, Inc. operates a large and rapidly growing constellation of CubeSats performing GNSS-based science and Earth observation. In a few short years, Spire has grown from a modest CubeSat kickstarter campaign to a paradigm-shifting provider of satellite data to NOAA, NASA, and other customers of Earth observations. Spire specializes in using science-quality observations of GNSS signals (e.g., GPS, GLONASS, Galileo, QZSS, etc.) to derive valuable information about the Earth environment. Currently, these observations include radio occultations to profile the neutral atmosphere with high accuracy and vertical resolution for applications such as NWP assimilation and climate monitoring, as well as to measure ionosphere slant total electron content and scintillation indices for space weather applications. As of May 2020, and after 21 deployments, Spire now has over 80, 3U Cubesats satellites capable of performing a variety of GNSS science, with plans to grow the constellation to well over 100 operational and continuously replenished satellites. Beginning in 2018, Spire began an effort to design and build the first of many GNSS bistatic radar (or GNSS-R) missions for Earth observations for a variety of applications, including soil moisture measurement, wetlands and flood inundation mapping, sea surface roughness and winds, and sea ice characterization. Following an agile model of rapid, iterative satellite development that has been refined over a few years to produce radio occultation payloads optimized for operation on ultra-small, 3U CubeSats, we adopted a very aggressive schedule to adapt the current Spire 3U bus and STRATOS GNSS science receiver to perform GNSS-R measurements, with a launch of satellites in December of 2019, and plans for two more GNSS-R satellites to be launched in 2020. We will discuss the goals and accomplishments of the Spire GNSS-R mission, the design and operational modes of the first batches of Spire GNSS-R satellites, and plans for a full, operational constellation of GNSS-R satellites. The Spire GNSS-R effort also has a parallel path that is already harnessing existing orbiting Spire satellites used for radio occultation to additionally perform grazing angle GNSS-R measurements for high-precision, phase-delay altimetry. This presentation will additionally discuss the unique experience of adapting the current constellation of radio occultation satellites to perform these new and valuable grazing angle GNSS-R Earth observations. We will introduce the concept of phase-delay altimetry and its potential to estimate surface heights on the order of 10 cm using observations of coherent GNSS signals reflected from various Earth surfaces. We will also show sea ice products derived from these new observations. Finally, we will discuss Spire’s potential to rapidly proceed with these measurements from research to operations and to make them available as a new set of Earth observations.
