HydroGNSS will be the first European Space Agency Scout science mission in orbit, with a launch scheduled for 2025.
HydroGNSS (Hydrology from Global Navigation Satellite Systems) comprises two small satellites that will provide data over land about the presence or absence of water – from moisture levels in soil, to flooding, to vegetation density and the freezing of the surface layer above permafrost.
The mission also sets out to demonstrate that reliable climate data can be collected in a cost-effective way. An objective of the European Space Agency (ESA) Scout programme is to demonstrate that science missions can be delivered using small satellites within three years for a maximum cost of €30m. The programme covers the development of the space and ground segments, launch and in-orbit commissioning.
Mission facts
- The HydroGNSS instrument uses a technique called GNSS Reflectometry (GNSS-R). ‘SatNav’ signals from GPS and Galileo satellites are exploited as if radar sources, and the instrument records the strength of their reflections off the Earth’s surface.
- The mission introduces innovative GNSS-R measurements, including dual frequency, polarimetry and a high-resolution measurement channel.
- Each satellite is just 50cm x 50cm x 70cm, the size of a small filing cabinet, and weighs around 65kg.
- The two satellites will be in a sun-synchronous orbit at 550km altitude, phased 180 degrees apart.
Applications
From the two satellites’ GNSS-R readings, scientists will derive measurements of a number of climate variables through different processing techniques including neural networks (an AI method).
HydroGNSS will provide data for climate, agricultural and weather forecasting, insights into the capacity of permafrost and wetlands to absorb CO2 and/or release methane, flood risk, the health of wetlands and forest biomass.
Data from the mission will be owned by the ESA and distributed on a free and open basis after a commissioning period.
What are the benefits?
Hydrological knowledge is vital for society, now and increasingly for the future. The presence or absence of water in or on the land has a profound impact on agriculture, biodiversity, flood preparedness, climate and weather.
Two important missions dedicated to global soil moisture measurements – ESA’s SMOS (Soil Moisture and Ocean Salinity) and NASA’s SMAP (Soil Moisture Active Passive) – are reaching the end of their life, with no immediate replacements. HydroGNSS provides an affordable way to help address this imminent gap.
HydroGNSS will also measure forest biomass at high latitudes in areas that cannot be reached by the upcoming ESA Biomass mission.
As secondary objectives, HydroGNSS will measure winds over the ocean and sea ice extent, and its innovative global measurements may yet find new applications.
The technology is low cost and lends itself to a future affordable and sustainable constellation of satellite sensors, increasing temporal and spatial resolution with each new satellite.
UK Expertise
The GNSS reflectometry technology behind the mission has been a UK success story. An early experiment was flown on the UK-DMC satellite in 2003 by Surrey Satellite Technology Ltd (SSTL) Guildford, Surrey in partnership with the University of Surrey and the National Oceanography Centre (NOC). This demonstrated that GPS reflections could be sampled from space and used for sensing over ocean, ice and land. With support from a CEOI call, SSTL developed a more advanced instrument that was able to process reflections on-board. This was flown on the UK Space Agency-supported TechDemoSat-1 in 2014 and, with support from ESA, enabled large volumes of measurements to be collected and distributed to researchers across the world.
NASA selected the CYGNSS concept for Earth Venture-2 in 2012, aiming to measure cyclones over the ocean from a constellation of 8 small satellites using SSTL’s GNSS-R instrument. Launched in 2016, the CYGNSS mission has been long-lived, outstandingly successful and established the credentials of GNSS-R for remote sensing and furthermore highlighting the potential for soil moisture measurement over land.
The UK is well-known as a leader in small satellites. SSTL is the prime for the HydroGNSS Scout mission and is providing the instrument, the satellites and the ground segment. Martin Unwin, Principal GNSS Engineer at SSTL, is the industrial principal investigator for the mission, and Executive Officer of the HydroGNSS Science Advisory Group.
The HydroGNSS science team includes experts from across Europe who provide processors for the HydroGNSS Payload Data Ground Segment.
The UK partners in the team are Giuseppe Foti in NOC, developing the secondary processor for ocean applications, and Paul Blunt at the Nottingham Geospatial Institute in the University of Nottingham, supporting the development of advanced on-board signal processing.
International Science Team Partners
European Space Agency (Customer)
Sapienza University of Rome, Italy
Tor Vegata University of Rome, Italy
Institute of Space Sciences, Spain
Institute of Applied Physics, Italy
Finnish Meteorological Institute, Finland
Vienna University of Technology, Austria
Insights
“Soil moisture has emerged as a critical climate and agricultural measure. Studies show that improved space observations, combined with models, could transform knowledge of today’s water availability and future projections from droughts to soil saturation.”
– Professor John Remedios, Director National Centre for Earth Observation (NCEO)
“As well as targeting important climate variables, GNSS Reflectometry continues to surprise. We are ready to expect the unexpected in uncovering new applications from the innovative measurements that will be taken.” – Dr Martin Unwin, HydroGNSS Industrial Principal Investigator
