The IceSat-2, which was sent into orbit on September 15 to accurately determine the shape of the Earth’s ice sheets now has a new mission, making height maps. This includes mapping the height of all the features that constitute the Earth’s topography; including land, rivers, lakes, forests and even the ocean floor.
The IceSat-2 only carries one instrument, a green laser that weighs half a tonne, and shoots 10,000 pulses of light every second. Each of these shots go down to Earth and bounce back to the satellite. The time taken for the light to complete its journey is what determines the height of the reflecting surface. The system is capable of detecting behaviour in areas that are considered beyond the vision of traditional satellites. It uses only 150 photons (light particles) to calculate heights, and is able to produce an elevation level that is accurate to two centimeters.
This optical “tape-measure” will also be used to detect elevation changes in Antarctica and Greenland which could indicate melting. It can also see the forest canopy and the ground underneath, which will enable new assessments of the amount of carbon stored in the Earth’s vegetation.
“We’re resolving every valley in the mountains,” said team-member Ben Smith from the University of Washington, Seattle. “These have been really difficult targets for altimeters in the past, which have often used radar instead of lasers and they tend to show you just a big lump where the mountains are. But we can see very steeply sloping surfaces; we can see valley glaciers; we’ll be able to make out very small details.”
Already a project is being developed to use IceSat to map the near-shores of about 100 small islands in the Pacific.
“You need to know the bathymetry to understand how waves will move on to the reefs and atolls,” explained Sinéad Farrell from the University of Maryland. “If you have storm surges, for example, you need to know those depths to accurately model what those waves will do; and currently there’s almost no bathymetry data at all for these islands.”