Spire's new GNSS-R soil moisture products collected from small and innovative Earth observing satellites

Spire Global operates the world’s largest and rapidly growing constellation of CubeSats performing GNSS based science and Earth observation. The Spire constellation, performs a variety of GNSS science, including radio occultation (GNSS-RO), ionosphere and space weather measurements, and precise orbit determination. In December 2019, Spire launched two new satellites to perform GNSS reflectometry (GNSS-R), with plans for two more GNSS-R satellites to be launched in mid-2020. Due to its agility and rapid launch cycle, averaging launches of four to eight satellites every six weeks, Spire has the unique ability to improve performance and add capabilities on-orbit that are impossible with traditional, risk-averse satellite missions. GNSS-R is a relatively new technique based on a passive bistatic radar system. The potential of space-borne GNSS-R observations for ocean and land applications has been demonstrated by other GNSS-R missions, including the NASA Cyclone Global Navigation Satellite System (CYGNSS) and the UK’s Technology Demonstration Satellite, TechDemoSat (TDS-1). We present initial results from these new Spire GNSS-R satellites that are primarily focused on retrieving soil moisture but also estimate other Earth surface properties such as ocean wind speeds and flood inundation/wetland mapping. Prior to the launch of Spire’s GNSS-R satellites and in preparation for Level-2 data production, we developed algorithms and processing chains for land applications. We will present Spire's soil moisture retrieval method using CYGNSS observations. We evaluated the implemented soil moisture change detection algorithm by comparing the Spire’s daily soil moisture product with NASA’s Soil Moisture Active Passive (SMAP) observations and in-situ soil moisture measurements. The results of study indicate remarkable retrieval skills of the GNSS-R technique for soil moisture monitoring at a medium spatial resolution. Spire’s GNSS-R satellites are tuned for land applications with a series of hardware and software optimizations for better signal calibration and acquiring many more data per satellite compared to CYGNSS. A more robust GNSS-R soil moisture retrieval at finer spatial resolution will be possible in the near future after having more Spire satellites in orbit. Spire’s current and future GNSS-R satellites will provide unprecedented sub-daily global coverage and fine spatial resolution. Such intensive data acquisition is of great importance for many land and ocean applications.