Publications
Spatialization and analysis of the GNSS-R measurements around of the Cordouan lighthouse
Research around the Cordouan Lighthouse in the Bay of Biscay reveals significant tidal variations in sea level measurements using GNSS reflectometry (GNSS-R). However, submerged sandy banks at low tide disrupt these measurements. The study spatialized GNSS reflection points to distinguish between sandy and rocky areas, creating a map of water height estimates based on reflection point positions. By analyzing 1-second Signal-to-Noise-Ratio (SNR) data over sliding elevation windows and correcting atmospheric delay effects, the team reduced dispersion in water heights by a factor of two. The findings show high variability (over one meter) and elevated mean water heights in the eastern part, consistent with known shoals, while oceanic areas exhibit much smaller variations. This distinction is further emphasized by differences between low and high tides.
Reflectometry With an Open-Source Software GNSS Receiver: Use Case With Carrier Phase Altimetry
A novel approach using open-source GNSS software demonstrates centimeter-level precision in carrier phase altimetry by extending coherent integration time (CIT) beyond the standard 20-ms limit. This method, tested at the Cordouan Lighthouse and during a high-altitude flight over a lake, enables robust measurements of amplitude ratio and differential carrier phase between direct and reflected signals. The findings highlight the potential for precise altimetry applications, including ocean surface wind and wave height retrieval, as well as environmental monitoring such as soil roughness and snow/ice characteristics. By leveraging signal processing techniques like bit sign wiping, this research advances GNSS reflectometry as a versatile tool for remote sensing.
Simulations of direct and reflected wave trajectories for ground-based GNSS-R experiments
Simulations reveal that the choice of Earth's surface model significantly impacts the accuracy of GNSS-R (Global Navigation Satellite System Reflectometry) measurements, with planimetric differences averaging 9 cm for satellite elevation angles above 10° and 13.9 cm between 5° and 10°. The study also highlights substantial errors due to angular refraction from the troposphere, which can reach up to 116 m in planimetric terms when the receiver height exceeds 300 m. Conducted at two test sites—Cordouan Lighthouse in France's Gironde estuary and Lake Geneva on the Franco-Swiss border—the research underscores the critical role of digital elevation models (DEMs) in improving measurement precision, with average planimetric differences of 6.3 m without DEM integration. The simulator developed for this study provides tools to optimize GNSS-R receiver placement for monitoring water levels and other surface variations.
Simulations of direct and reflected waves trajectories for in situ GNSS-R experiments
A simulator was developed to accurately determine the reflection points of Global Navigation Satellite System (GNSS) signals on Earth's surface, offering a unique method to monitor water level variations. The study found that geometric differences between reflection points, when considering Earth as a sphere or ellipsoid, averaged 44 cm for satellites with elevation angles greater than 10° and 1 m for those between 5° and 10°. Integration of Digital Elevation Models (DEM) significantly impacted reflection point accuracy, with errors reaching up to 3.80 m without DEM integration at a minimum elevation angle of 5°. Tropospheric effects also introduced substantial errors, increasing from 43 cm at a 5 m receiver height to 103 m at 300 m. These findings underscore the importance of precise Earth representation and atmospheric corrections in GNSS-R experiments.
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