SSTL’s HydroGNSS satellite gets green light for climate mission

The small satellite will measure climate variables using GNSS Reflectometry

The European Space Agency (ESA) has selected HydroGNSS from Surrey Satellite Technology Ltd. (SSTL) for its second Scout Earth Observation small satellite mission. HydroGNSS is a 40-kg satellite that will be built and operated by SSTL.

ESA selected the first ESA Scout satellite, ESP-MACCS, in December 2020. ESP-MACCS focuses on understanding and quantifying processes in the upper atmosphere over the tropics — processes that play an important role in the overall evolution of the atmosphere.

HydroGNSS will take measurements of key hydrological climate variables, including soil moisture, freeze thaw state over permafrost, inundation and wetlands, and aboveground biomass, using GNSS reflectometry. It will complement missions such as ESA’s SMOS and Biomass, Copernicus Sentinel-1 and NASA’s SMAP.

Both small satellites are expected to be the first in a series of ESA Scout missions demonstrating how small satellites on a budget of less than €30 million and a three-year schedule can play an important role in Earth observation, and be scaled up for future missions.

Knowledge of these variables helps scientists understand climate change and contributes towards weather modelling, ecology mapping, agricultural planning and flood preparedness.

“SSTL pioneered GNSS reflectometry, providing the payloads on TechDemoSat-1 and the NASA CYGNSS mission for measuring ocean wind speeds, and I am delighted that we will now launch the first satellite mission specifically addressing hydrological measurements using this innovative technique,” said Phil Brownnett, SSTL managing director.

Previously, addressing hydrological variables such as these has required sizable and higher cost satellites with large aperture antennas, but GNSS reflectometry uses existing signals from GNSS as radar signal sources. These signals are reflected off the land, ice and ocean and can be collected by a low power receiver on a small satellite in low Earth orbit, and used to yield important geophysical measurements.

Image: SSTL

SSTL is working closely with partners to tackle the scientific and technological challenges involved. Partners include Sapienza, Tor Vergata and IFAC-CNR in Italy; FMI in Finland; IEC/IEEC in Spain; and NOC and the University of Nottingham in the United Kingdom (UK),

“The decision to implement HydroGNSS after ESP-MACCS demonstrates that the Earth observation community is very interested in the concept of Scout missions. We are confident that this interest will further flourish when we see the first data in 2024,” said Toni Tolker-Nielsen, ESA’s acting director of Earth Observation Programmes.

As well as the already established GNSS-Reflectometry measurements, new techniques will be explored on HydroGNSS, including use of Galileo signals, dual polarization, dual frequency and recovery of coherently reflected components. These new measurements are expected to improve the separation, resolution and quality of the climate variables under observation.

The HydroGNSS mission exemplifies the UK’s innovation in climate change research, according to SSTL. The 26th United Nations Climate Change Conference takes place in the UK Nov. 1-12.

Image: SSTL

“The UK is leading the way in using space to tackle climate change, with Earth Observation satellites providing some of the most important data to monitor our environment as we build back greener,” said Science Minister Amanda Solloway. “Using a UK satellite just the size of a microwave oven, this pioneering mission will build on the UK’s expertise in space research by measuring changes in the Earth’s water, providing crucial information to address climate change, improve farming and support wider disaster management.”

HydroGNSS paves the way for an affordable future constellation that can offer measurements with a temporal-spatial resolution not accessible to traditional remote-sensing satellites, thus offering new capacity to monitor very dynamic phenomena and helping to fill the gaps in our monitoring of the Earth’s vital signs for the future.

Featured image: SSTL