A recently-launched satellite mission is now proving a valuable addition to Antarctic monitoring efforts, according to work published this week in The Cryosphere.
The study, carried out by CPOM researchers alongside European Space Agency (ESA) and industry partners, shows the potential of Sentinel-3 – one of the EU Copernicus satellite missions – to contribute towards long-term ice sheet monitoring programmes.
From its orbit 815 km above the Earth, Sentinel-3 is able to detect the height of the ice surface at the remote Lake Vostok test site in East Antarctica to within tens of centimetres.
The scientists also found that Sentinel-3 could detect where the ice surface was rapidly lowering, establishing the satellite’s credentials as a new platform which can help to monitor Antarctica’s contribution to sea level rise.
Determining how well Sentinel-3 functions over ice sheets is particularly important given that CryoSat-2, ESA’s dedicated polar mission, is already operating well beyond its planned lifetime.
CryoSat-2 is designed to fly in a unique orbit, maximising coverage of coastal areas of the ice sheet, and mapping the regions close to the North and South Poles that were beyond the reach of previous satellites.
Although Sentinel-3 – which has to balance many tasks – cannot match this coverage, it still holds potential as a valuable long-term monitoring platform for decades to come.
Lead author Dr Mal McMillan, CPOM scientist at Lancaster University, said: “Although the Sentinel-3 altimeter was primarily designed to monitor the oceans, we wanted to test how well it works over ice, and to see whether it is able to detect signs of ice sheet change. Through the support offered by ESA’s Scientific Exploitation of Operational Missions element, we have been able to study the performance of the Sentinel-3 mission for several years now, and we are pleased to be able to publish these results”.
He added: “From what we can see here, with just two years’ worth of data, Sentinel-3 is going to be a very useful tool for surveying the Antarctic ice sheet.”
Sentinel-3 uses a radar technique called Delay-Doppler altimetry to make high resolution measurements of the height of the ice sheet.
Where the ice is relatively flat, Sentinel-3 could map its height to within 10 cm of measurements taken by aircraft, as part of NASA’s Operation Icebridge campaign.
Dr McMillan explained: “This level of accuracy means that we can also use Sentinel-3 to track important features on the ice surface, like the fingerprint of active subglacial lakes draining and refilling beneath several kilometres of ice.”
Using radar satellites like Sentinel-3 over ice nonetheless has its challenges. For example, measurements over Antarctica’s steeper, craggy coastal areas were less accurate because of how the rough landscape affects the radar signal.
Future research into Sentinel-3’s performance, as well as further improvements to data processing, will help take these effects into account. In the meantime, Sentinel-3 has already shown its value as a new tool for detecting ice sheet change.
Co-author Jérôme Benveniste of the European Space Agency summarised: “We are delighted with the early promise shown by Sentinel-3 for ice sheet monitoring, and are increasingly confident that it will be a long-term asset to climate science”.
The full paper is: McMillan, M. et al. (2019) Sentinel-3 Delay-Doppler altimetry over Antarctica, The Cryosphere 13, 1-14 doi:10.5194/tc-13-1-2019
Dr McMillan is available for comment (tel: +44 (0)1524 592595; email: email@example.com).
The Sentinel-3A satellite, part of the European Union’s Copernicus Programme was launched on 16 February 2016, followed by Sentinel-3B on 25 April 2018. Each satellite provides coverage up to a latitude of 81.35ᵒ, yielding regular, monthly observations of much of Earth’s polar ice sheets. Sentinel-3 is unique in being the first mission to operate in high-resolution Delay-Doppler (or Synthetic Aperture Radar—SAR) mode across the entire ice sheet.
The work was supported by the UK NERC Centre for Polar Observation and Modelling, ESA’s Sentinel-3 Performance Improvement for Ice Sheets (SPICE) study and the Sentinel-3 Mission Performance Centre.