# HydroGNSS (ESA Scout)
*missions*

Two-microsat ESA Scout constellation launched November 2025; GNSS-R instruments receive GPS and Galileo reflections to measure soil moisture, freeze-thaw state over permafrost, wetland inundation, and above-ground biomass at 500-600 km SSO.

## Specifications
- **operator**: esa
- **current status**: commissioning
- **actual launch**: 2025-11-28
- **orbit type**: SSO 550 km 98-degree inclination
- **tasking supported**: false
- **launch vehicle**: spacex-falcon-9
- **entity type**: mission
- **last verified date**: 2026-06-11
- **verified by**: agency-doc
- **claim status**: unclaimed
- **provider**: esa
- **attributes**: {"operator":"esa","current_status":"commissioning","actual_launch":"2025-11-28","orbit_type":"SSO 550 km 98-degree inclination","tasking_supported":false,"summary":"Two-microsat ESA Scout constellation launched November 2025; GNSS-R instruments receive GPS and Galileo reflections to measure soil moisture, freeze-thaw state over permafrost, wetland inundation, and above-ground biomass at 500-600 km SSO.","launch_vehicle":"spacex-falcon-9"}
- **relevance**: in-scope

## Editorial
HydroGNSS is an ESA Scout mission consisting of two microsatellites launched on 28 November 2025 into a sun-synchronous orbit at 550 km altitude and 98-degree inclination. As of mid-2026 the mission is in the commissioning phase, with science data release expected in July 2026.[^esa-hydrognss-launch][^sstl-hydrognss-2026]

Each spacecraft carries an SGR-ReSI-Z GNSS reflectometry receiver designed to measure reflected GPS and Galileo signals and to derive soil moisture, freeze-thaw state of permafrost, wetland inundation extent, and above-ground biomass. The SGR-ReSI-Z is a new generation of the SGR-ReSI instrument flown on TechDemoSat-1, which demonstrated spaceborne GNSS-R ocean wind retrieval in 2014, and builds on techniques validated on the CYGNSS constellation.[^eoport-hydrognss]

The two-satellite configuration provides repeat coverage to support seasonal monitoring of permafrost dynamics and flood inundation in high-latitude and wetland regions.[^eoport-hydrognss][^esa-hydrognss-launch]

## Sources
- [eoport-hydrognss] | HydroGNSS/Scout-2 mission overview, eoPortal | https://www.eoportal.org/satellite-missions/hydrognss | tier=agency-doc | accessed=2026-06-11
- [esa-hydrognss-launch] | ESA HydroGNSS launched to scout for water | https://www.esa.int/Applications/Observing_the_Earth/FutureEO/HydroGNSS/ESA_s_HydroGNSS_mission_launched_to_scout_for_water | tier=operator-press | accessed=2026-06-11
- [sstl-hydrognss-2026] | HydroGNSS satellites proving in-orbit capabilities, SSTL 2026 | https://www.sstl.co.uk/media-hub/latest-news/2026/hydrognss-satellites-proving-in-orbit-capabilities | tier=operator-press | accessed=2026-06-11

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Source: https://eo-atlas.org/missions/hydrognss
Maintainer: SpectraWorks B.V. (CC-BY 4.0)