Introducing HydroGNSS
The HydroGNSS Scout mission comprises two identical satellites that were launched on 28 November 2025.
HydroGNSS is the first in ESA’s new family of Scout missions, developed under the Earth Observation FutureEO programme.
While the well-established Earth Explorer missions focus on large-scale research, Scout missions introduce a complementary New Space approach: small, agile satellites designed to deliver value-added science.
This is achieved by either miniaturising proven space technologies or by testing innovative observation techniques. Crucially, Scouts emphasise speed, ensuring that new ideas are demonstrated and deployed rapidly.
The HydroGNSS satellites use an innovative technique called Global Navigation Satellite System (GNSS) reflectometry. Navigation satellites such as GPS and Galileo transmit L-band microwave signals, which change when reflected off Earth’s surface.
HydroGNSS compares these reflected signals with the direct GNSS signals to extract valuable information on geophysical parameters related to the water cycle.
The mission focuses on four crucial parameters, recognised as Essential Climate Variables or parameters closely related to them: soil moisture, freeze–thaw state over permafrost, inundation and above-ground biomass.
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These data are vital for weather forecasting, agriculture, flood prediction, and for improving our understanding of wetlands, permafrost dynamics and forest carbon storage. In addition, HydroGNSS provides secondary measurements of ocean wind speed and sea-ice extent.
Information collected by HydroGNSS matters because changes in the global water cycle pose serious risks to both the environment and human societies.
Extreme weather events such as droughts and floods can cause water scarcity, disrupt food production, damage ecosystems, and threaten health and infrastructure.
By delivering timely and reliable data, HydroGNSS helps better understand and respond to these global challenges.
Surrey Satellite Technology Ltd in the UK is ESA’s prime contractor for HydroGNSS. SSTL is also responsible for operating the satellites in orbit and for distributing the data.
