Melting ice

Measuring ice melt

In mid September NASA launched a satellite that will monitor the rate Earth's ice caps are melting. And despite its vast distance from earth, the sophisticated $1bn instrument can measure the height and thickness of ice sheets to within one centimetre. 

NASA’s Ice, Cloud and land Elevation Satellite-2 (ICESat-2) will measure the average annual elevation change of land ice covering Greenland and Antarctica, capturing 60,000 measurements every second. 

By calculating the length of time for the laser beams to bounce back, NASA can confidently measure the heights of ice sheets as well as the thickness of remaining sea ice.

In the course of three months the satellite – the size of a smart car - will orbit more than 1,000 paths while focusing six lasers at the Arctic and Antarctica’s ice sheets.

“The new observational technologies of ICESat-2 will advance our knowledge of how the ice sheets of Greenland and Antarctica contribute to sea level rise,” explained Michael Freilich, director of the Earth Science Division in NASA’s Science Mission Directorate.

The concept is not new. ICESat-2 is an improvement on NASA's 15-year record of monitoring the change in polar ice heights, which started in 2003 with the first ICESat mission and continued in 2009 and found that in that period the measured sea ice lost 40 per cent of its thickness.

ICESat-2 is described as representing a major technological leap in NASA’s ability to measure changes in ice height. Its Advanced Topographic Laser Altimeter System (ATLAS) measures height by timing how long it takes individual light photons to travel from the spacecraft to Earth and back, collecting more than 250 times as many height measurements as its predecessor.

ATLAS will fire 10,000 times each second, sending hundreds of trillions of photons to the ground in six beams of green light. The roundtrip of individual laser photons from ICESat-2 to Earth’s surface and back is timed to the billionth of a second to precisely measure elevation.

Tom Neumann who is NASA’s deputy project scientist for the special mission said  “In the time it takes someone to blink, sort of half a second, ICESat-2 is going to collect 5,000 measurements in each of its six beams, and it’s going to do that every hour, every day … it’s a tremendous amount of data.”

The data gained will be put to practical use, with the measurements of snow and river heights potentially helping local governments plan for floods and droughts, and sea ice thickness measurements could be integrated into forecasts issued by the US Navy for navigation and sea ice conditions.

ATLAS will also measure both the tops of trees and the ground below, which – combined with existing datasets on forest extent – will help researchers estimate the amount of carbon stored in the world’s forests.

Apparently several federal US agencies are keen to review the satellite data when it starts rolling in in October.