Development of a new instrument that could use satellite navigation signals to determine sea-surface roughness, ice characteristics, or soil moisture content has received a boost from the Centre for Earth Observation Instrumentation (CEOI). The SSTL-led team will continue the development in a CEOI funded project. The CEOI is an initiative to develop the next generation of Earth observation instruments, funded by the Natural Environment Research Council (NERC) and Technology Strategy Board (TSB).

The new project will continue the development of the instrument that exploits signals from the Global Navigation Satellite Systems (GNSS) satellites that are reflected from land, ice and ocean.

The instrument, which is named SGR-ReSI, will utilise a flexible multi-channel receiver for reflected GNSS signals for surface sea-state measurements. It is led by SSTL working with the University of Surrey, the University of Bath, the National Oceanography Centre in Southampton, and Polar Imaging Limited.

The objective of the current project is to continue development of an instrument that can be applied to both Earth surface reflectometry (ocean, land and ice) and atmospheric sounding, and to begin planning for experimental and operational use on a forthcoming satellite mission.

The prototype will incorporate a multi-antenna receiver for both GPS and Galileo signals on two frequencies that is evolved from the successful GNSS-R receiver flown SSTL’s UK-DMC satellite. It will have re-configurable processing capabilities and allow processing and data collection in real time.

The instrument may be flown in space as an approved addition to the future SMOSOps operational mission to measure soil moisture and ocean salinity, or through SSTL’s own satellite launching capabilities.

How it works

Global Navigation Satellite Systems (GNSS) such as the current GPS constellation and Europe's imminent Galileo system beam signals to the Earth from orbit. While their purpose is to provide satellite navigation for our transport or ramblers, these signals can also contain information that is valuable to scientists studying the Earth from space.

Remote sensing is made possible by analysing the reflected signal with an instrument flying on a separate small satellite. Using this elegant new technique important scientific data can be collected on the nature of the reflecting surface such as the sea-surface roughness, ice characteristics, or soil moisture content and also the properties of our atmosphere.

Science and operational need

GNSS signals for Earth Observation have already been well established as useful – for example in atmospheric sounding to measure tropospheric temperature, pressure and humidity.

These GNSS signals have also proved their worth for Earth Surface Reflectometry. In an experiment from an SSTL satellite in 2003, GPS signals reflected off the Earth surface were used to yield geophysical information about the scattering properties of the ocean, ice and land surfaces. GNSS signals reflected from the ocean contain information about both sea surface height (altimetry) and ocean roughness (sea state and scatterometry).

Ocean roughness impacts many areas of ocean and atmospheric science and is important for operational ocean and weather forecasting. Air-sea exchanges of gases, for example, are controlled by surface roughness, so that better sampling would have a direct impact on our understanding of the magnitude and distribution of atmospheric carbon dioxide (CO₂) uptake by the ocean. There are also important applications in the prediction of high winds, dangerous sea states, risk of flooding and storm surges.