GNSS Reflectometry Applications in Earth Observation

Global Navigation Satellite System Reflectometry (GNSS-R) exploits signals transmitted by constellations such as GPS, Galileo, GLONASS and BeiDou after they reflect from the Earth’s surface. These reflections, which carry imprints of surface roughness, dielectric properties and geometry, can be measured by bespoke receivers on satellites, aircraft or ground stations. Over the past decade, GNSS-R has emerged as a versatile, low-cost technique for quantifying a wide range of environmental variables. On the oceans, GNSS-R supports altimetry, wind-speed estimation and the detection of surface currents. Over land, it enables retrieval of soil moisture, flood extent and snow or ice thickness. In vegetated regions, reflectometry can infer biomass density and canopy structure. Its all-weather capability and high revisit frequency make GNSS-R particularly attractive for monitoring dynamic processes such as tropical cyclone intensity, wetland inundation and rapid post-disaster flood mapping. Advances in receiver design, signal processing and data assimilation are driving new applications in climate monitoring, hydrology, cryospheric science and ecosystem studies, with planned multi-system constellations set to enhance spatial coverage and measurement precision globally.

Research from Nature Portfolio

Recent studies have demonstrated the transformative potential of a small-satellite GNSS-R constellation for environmental monitoring. One pioneering effort described an ensemble of microsatellites equipped with GNSS receivers that sample L-band reflections at high temporal resolution. By leveraging orbital manoeuvres via differential drag and continuous GPS emulation, this platform yields frequent sea-state observations, soil moisture estimates and flood detection. Initial on-orbit results confirmed robust retrievals of ocean wind speed and surface saturation over land, heralding a new paradigm in low-cost, high-throughput Earth-observation. In flood-mapping applications, researchers repurposed these GNSS-R signals to delineate inundation during a major hurricane season. A straightforward thresholding of reflectivity data produced spatially detailed flood extents, revealing areas of significant land saturation that would otherwise be obscured by cloud cover or vegetation. This work underscores the capacity of GNSS-R to augment existing hydrological monitoring networks with rapid, wide-area assessments during extreme weather events.

Research from all publishers

A comprehensive review in Satellite Navigation has synthesised recent advances across GNSS-R theory, instrumentation and data analysis. It highlights improvements in delay-Doppler mapping, refined bistatic radar models and novel signal-processing algorithms that enhance retrieval accuracy for wind speed, sea-surface height, soil moisture and ice thickness. The authors identify emerging challenges such as multi-GNSS integration, polarimetric measurements and the development of specialised airborne and ground-based receivers for near-field sensing. Weekly mapping of tropical wetland inundation using spaceborne GNSS-R has also been reported, where reflectivity data combined with biomass maps enabled the generation of high-frequency water-fraction time series. This approach captured seasonal flood dynamics with global root-mean-square deviations below 15%, outperforming passive optical sensors under dense vegetation and persistent cloud cover. Seminal work on a pioneering GNSS-R mission from the mid-2010s demonstrated the feasibility of ocean wind retrieval from reflected GPS signals, laying the groundwork for successor missions and operational wind-speed products with precision approaching that of conventional scatterometers.

GNSS Reflectometry Applications in Earth Observation publication trend

The graph below shows the total number of articles in gnss reflectometry applications in earth observation across all publications each year (not limited to Nature Index journals).

Technical terms

GNSS Reflectometry (GNSS-R): A remote-sensing technique that analyses signals from navigation satellites after they reflect from the Earth’s surface to infer geophysical properties.

Bistatic Radar: A radar configuration in which the transmitter and receiver are in separate locations, here referring to GNSS satellites as transmitters and dedicated receivers as sensors.

Delay-Doppler Mapping: A processing method that resolves reflected signals in time delay and frequency shift to determine the spatial distribution and motion of reflecting features.

Reflectivity: The ratio of power in a reflected GNSS signal to the power of the direct signal, related to surface roughness and dielectric constant.

Signal-to-Noise Ratio (SNR): The measure of signal strength relative to background noise, often used to infer geophysical parameters from GNSS-R data.

References

1. Remote sensing and its applications using GNSS reflected signals: advances and prospects. Satellite Navigation (2024).
2. Weekly mapping of surface water extent in the intertropical wetlands using spaceborne GNSS reflectometry. Journal of Hydrology (2023).
3. Spaceborne GNSS reflectometry for ocean winds: First results from the UK TechDemoSat‐1 mission. Geophysical Research Letters (2015).
4. A New Paradigm in Earth Environmental Monitoring with the CYGNSS Small Satellite Constellation. Scientific Reports (2018).
5. CYGNSS data map flood inundation during the 2017 Atlantic hurricane season. Scientific Reports (2018).