# GNSS reflectometry (GNSS-R)
*methodologies*

Retrieves surface properties (ocean wind speed, soil moisture, sea ice extent, surface roughness) from reflected L-band navigation signals; good for global ocean wind monitoring and soil moisture at low constellation cost.

## Specifications
- **family**: GNSS-R
- **requirements envelope**: {"kind":"geometric","gsd_max":25000,"repeat_pass_geometry":false,"polarisation_modes":["L-band"]}
- **entity type**: methodology
- **last verified date**: 2026-06-11
- **verified by**: sw
- **claim status**: unclaimed
- **attributes**: {"family":"GNSS-R","summary":"Retrieves surface properties (ocean wind speed, soil moisture, sea ice extent, surface roughness) from reflected L-band navigation signals; good for global ocean wind monitoring and soil moisture at low constellation cost.","requirements_envelope":"{\"kind\":\"geometric\",\"gsd_max\":25000,\"repeat_pass_geometry\":false,\"polarisation_modes\":[\"L-band\"]}"}
- **technology**: gnss-signal-sensing

## Editorial
GNSS reflectometry (GNSS-R) is a passive bistatic radar technique that exploits navigation signals from GPS, Galileo, and BDS constellations as signals of opportunity. Reflected GNSS waveforms are captured by a nadir-facing antenna and processed into Delay-Doppler maps (DDMs), which encode surface roughness and dielectric properties to retrieve ocean wind speed, soil moisture, sea ice extent, and surface inundation.[^cygnss-nature-2018]

TechDemoSat-1 (launched July 2014) carried the SGR-ReSI instrument developed by Surrey Satellite Technology Ltd and demonstrated the first spaceborne GNSS-R measurements of ocean wind speed and sea ice classification.[^sstl-tds1] CYGNSS (launched December 2016) scaled the approach to an eight-microsatellite constellation in a 520 km, 35-degree-inclination orbit, enabling near-daily tropical coverage. Its DDMI instrument delivers L2 ocean wind speed, L3 soil moisture, and L3 flood inundation products distributed via NASA PO.DAAC.[^cygnss-rs-2021] ESA's HydroGNSS Scout constellation (launched November 2025) extends the application set to soil moisture, freeze-thaw state, wetland inundation, and above-ground biomass.[^esa-hydrognss] Spire Global operates a commercial CubeSat constellation with GNSS-R capability, offering Spire Soil Moisture Insights as an operational commercial product.

L-band navigation signals penetrate vegetation canopy more effectively than shorter-wavelength active radar, making GNSS-R an efficient complement to dedicated active microwave sensors for land surface monitoring. The technique requires no onboard transmitter, which substantially reduces instrument mass and power compared to monostatic active radar.

## Sources
- [cygnss-nature-2018] | A New Paradigm in Earth Environmental Monitoring with the CYGNSS Small Satellite Constellation (Scientific Reports 2018) | https://www.nature.com/articles/s41598-018-27127-4 | tier=peer-reviewed | accessed=2026-06-11
- [cygnss-rs-2021] | The CYGNSS Mission: On-Going Science Team Investigations (Remote Sensing 2021) | https://www.mdpi.com/2072-4292/13/9/1814 | tier=peer-reviewed | accessed=2026-06-11
- [esa-hydrognss] | HydroGNSS mission overview, ESA EO Gateway | https://earth.esa.int/eogateway/missions/hydrognss | tier=agency-doc | accessed=2026-06-11
- [sstl-tds1] | TechDemoSat-1 mission profile, Surrey Satellite Technology Ltd | https://www.sstl.co.uk/space-portfolio/launched-missions/2010-2019/techdemosat-1-launched-2014 | tier=operator-engineering | accessed=2026-06-11
- [wikipedia-gnssr] | Wikipedia: GNSS reflectometry | https://en.wikipedia.org/wiki/GNSS_reflectometry | tier=community | accessed=2026-05-22

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Source: https://eo-atlas.org/methodologies/gnss-reflectometry
Maintainer: SpectraWorks B.V. (CC-BY 4.0)