Great Bear Lake in the Northern Territories of Canada. Data acquired by Sentinel 2 on the 06/05/2016. Data courtesy by ESA/Copernicus.⠀
Two recently published scientific papers show uses of SAR data to measure different characteristics of ice in both the Arctic and Antarctic.
Firstly, a paper in the IEEE Transactions on Geoscience and Remote Sensing demonstrated how CryoSat data has been used to measure the thickness of lake ice in Canada.
This is a further repurposing of Cryosat-2’s mission as it was launched with the aim of measuring the thickness of ice sheets and marine ice cover using its Synthetic Aperture Radar (SAR)/Interferometric Radar Altimeter, known as SIRAL. It has a 250 m swath and can detect millimetre changes in the elevation of both ice-sheets and sea-ice.
This research for the first time uses SIRAL to measure the thickness of ice in the Great Slave Lake and the Great Bear Lake. These two lakes were chosen as they have flat and smooth surfaces to enable the radar reflections between ice-covered and ice-free areas to be easily distinguished. The results show a thickening of the ice during the winter, which was validated by in-situ measurements. Whilst these are large lakes, the researchers are confident it can be applied to smaller lakes enabling a study of the changes, and thickness, of lake ice over a year which are indicators of climate change. The importance of understanding this is that between fifteen and forty percent of North America’s Arctic and sub-Arctic regions are covered by lakes making them a vital resource for both people and wildlife.
NASA/UC Irvine map of ice velocity in Antarctica. Coloured lines indicate the direction of flow; background colours show speed. Credit: UCI/Jeremie Mouginot
The second piece of research is from the bottom of the world where a new map of Antarctic ice velocity has been developed by researchers from the University of California, Irvine and NASA’s Jet Propulsion Laboratory. The paper titled ‘Continent‐wide, interferometric SAR phase, mapping of Antarctic ice velocity’ by Mouginot, Rignot & Scheuchl (2019) was published in American Geophysical Union journal Geophysical Research Letters.
Surface ice velocity is a characteristic of glaciers and ice sheets that quantifies the transport of ice, and changes in this impact on ice sheet mass and sea level rises. Whilst previous maps have only covered 20% of the continent, the team have achieved 80% coverage with their new approach that is ten times more accurate than the previous maps.
They used SAR phase interferometry to detect small movements in snow and ice. It does require significantly more data than previous methods, including the data over the area at different angles, which is why it was necessary to use the multiple missions, in this case, six satellite missions:
- Canadian Space Agency’s Radarsat-1 and Radarsat-2;
- European Space Agency’s ERS-1, ERS-2 and Envisat ASAR; and
- Japan Aerospace Exploration Agency’s ALOS PALSAR-1.
The result is a map that shows movement to a level of 20 centimetres per year in speed and 5 degrees in annual flow direction for more than 70 percent of Antarctica. This will help better identify the boundaries between glaciers, ice-core drilling for climate models, inform ice sheet numerical models and improving understanding on how the Antarctica mass itself changes and evolves over time. The new map and related datasets are available for download here.
Satellite remote sensing comes into its own in measuring large scale, remote and difficult to reach such as these two polar regions.
