SSTL demonstrates new GNSS-R capabilities

Surrey Satellite Technology Ltd (SSTL) has successfully demonstrated GNSS-Reflectometry (GNSS-R) from its 18kg DoT-1 satellite. SSTL has pioneered the new field of GNSS-R with successful payloads on board TechDemoSat-1 and the CYGNSS constellation, and is continuing to develop the technology and data analysis in pursuit of this new science. The latest GNSS-R payload on-board the DoT-1 satellite is incorporated within the new small form factor Core Avionics module integral to all SSTL’s future satellite platforms. This innovation paves the way for any SSTL satellite that can accommodate a nadir pointing antenna to become part of a GNSS-R small-sat constellation.

GNSS Reflectometry is an Earth observation technique that uses GNSS signals as L-Band radar sources, allowing the satellite to take measurements of ocean wind speeds, polar ice and hydrological land parameters, at a higher spatial resolution and an order of magnitude lower cost than other methods.

This GNSS-R technology demonstration from SSTL’s DoT-1 satellite is also an important stepping stone for a proposed ESA Scout Mission Concept called HydroGNSS which comprises two 40kg satellites that collect data continually in near-polar orbits, taking hydrological measurements over the whole globe. The HydroGNSS mission concept makes advanced use of new GNSS Reflectometry techniques such as Galileo signals, dual polarisation, and coherent signal acquisition to measure 4 Essential Climate Variables (ECVs) over land: Soil Moisture, inundation, permafrost freeze/thaw, and biomass. HydroGNSS has been down-selected by ESA for a concept study, and the finally selected Scout mission will commence in 2021.

SSTL’s GNSS-R instrument collects and processes measurements into a “Delay Doppler Map” (DDM) that can be corrected and inverted into Level 2 products such as ocean wind speed, as has already been successfully demonstrated by the SSTL GNSS-R instruments on-board the TechDemoSat-1 and CYGNSS missions. The plot below shows results from data gathered by the DoT-1 satellite on 12th August 2020 and shows simultaneous “Delay Doppler Maps” from four separate GPS satellites. As this is a forward scattering technique, the stronger signals with redder peaks indicate a calmer ocean with lower wind speeds. Approximately 40 minutes of data were collected from the Pacific to the Antarctic to the Southern Ocean.

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