ESA Scout HydroGNSS Early Mission Results

The ESA Scout HydroGNSS mission, launched in December 2025 will provide measurements of key hydrological climate variables, including soil moisture, freeze–thaw state over permafrost, inundation and wetlands, and above-ground biomass, using a novel technique called Global Navigation Satellite System (GNSS) reflectometry. According to GCOS there is a shortage of high-quality soil moisture data, a key parameter linked to Essential Climate Variables; physical, chemical or biological variables that critically contribute to the characterization of Earth’ s climate.

Scout missions are a recent addition to the ESA Earth Observation Directorate, intended to deliver valuable science from small satellites. HydroGNSS was a rapid development mission with a budget of less than €30m incorporating NewSpace methods and is the first Scout mission to be launched. It comprises of two identical satellites with mass of about 72 kg each that were carried into a 530 km sun-synchronous orbit as part of a SpaceX Rideshare launch on 28th November 2025.

GNSS Reflectometry (GNSS-R) takes measurements of the Earth’s surface by collecting in orbit GNSS signals scattered off the Earth’s surface. GNSS-R has been developing rapidly as an L-Band remote sensing technology suitable for small satellites and continues to find applications over ocean, ice and land. HydroGNSS is primarily a land-sensing mission and has been developed to specifically address hydrological essential climate variables using GNSS-R. Results from the mission will be presented to show progress towards the Mission & Science Objectives. The industrial consortium features a fully European science team.