The TrickyScribe: National Aeronautics and Space Administration (NASA) is all set to launch into space the most advanced laser instrument of its kind, beginning a mission to measure changes in the heights of Earth’s polar ice. Ice, Cloud and land Elevation Satellite-2 (ICESat-2) is scheduled to launch from Vandenberg Air Force Base, California on September 15.
NASA’s ICESat-2 will measure the average annual elevation change of land ice covering Greenland and Antarctica to within the width of a pencil, capturing 60,000 measurements every second. “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,” said Director, Earth Science Division, Science Mission Directorate, NASA, Michael Freilich.
ICESat-2 will extend and improve upon NASA‘s 15-year record of monitoring the change in polar ice heights, which kicked off with the first ICESat mission in 2003 and continued with Operation IceBridge, an airborne research campaign that kept track of the accelerating rate of change in 2009.
The ICESat-2 represents a major technological leap in our ability to measure changes in ice height. Advanced Topographic Laser Altimeter System (ATLAS), used in ICESat-2, measures height by timing how long it takes individual light photons to travel from the spacecraft to Earth and back.
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“ATLAS required us to develop new technologies to get the measurements needed by scientists to advance the research,” said Project Manager, ICESat-2, Doug McLennan. Doug is currently stationed at NASA’s Goddard Space Flight Center. “That meant, we had to engineer a satellite instrument that not only will collect incredibly precise data, but also will collect more than 250 times as many height measurements as its predecessor,” Doug said.
How it works?
The 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.
With photons returning from multiple beams, ICESat-2 will get a much more detailed view of the ice surface than its predecessor, ICESat. If the two satellites were flown over a football field, in fact, ICESat would take only two measurements, one in each end zone, whereas ICESat-2 would collect 130 measurements between each end zone.
The ICESat-2 will measure ice heights along the same path in the Polar Regions four times a year as it revolves around Earth from pole to pole, providing seasonal and annual monitoring of ice elevation changes.
Tracking melting ice
Billions of tons of land ice melts and eventually flows into the oceans continuously, contributing to sea level rise worldwide. Contributions of melt from the ice sheets of Greenland and Antarctica alone, in recent the years, have raised global sea level by more than a millimeter annually, accounting for approximately one-third of observed sea level rise. Unfortunately, the rate is increasing.
The ICESat-2 will help researchers reduce the range of uncertainty in forecasts of the future sea level rise and connect those changes to climate drivers. It also will make the most precise polar-wide measurements to date of sea ice freeboard, which is the height of sea ice above the adjacent sea surface.
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This measurement is used to determine the thickness and volume of sea ice. Satellites routinely measure the area covered by sea ice and have observed an Arctic sea ice area decline of about 40 percent since 1980, but precise, region-wide sea ice thickness measurements will improve our understanding of the drivers of sea ice retreat and loss.
Perils of floating ice
Although floating sea ice doesn’t change sea level when it melts, its loss has different consequences. The bright Arctic ice cap reflects the Sun’s heat back into space. When that ice melts away, the dark water below absorbs that heat. This alters wind and ocean circulation patterns, potentially affecting Earth’s global weather and climate.
Measuring height of ocean, land surfaces
Beyond the poles, ICESat-2 will measure the height of ocean and land surfaces, including forests. The ATLAS is designed to 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. Researchers also will investigate the height data collected on ocean waves, reservoir levels, and urban areas.
Benefits of precise data
Potential data users have been working with ICESat-2 scientists to connect the mission science to societal needs. ICESat-2 measurements of snow and river heights could help local governments plan for floods and droughts. Forest height maps, showing tree density and structure, could improve computer models that firefighters use to forecast wildfire behaviour. Sea ice thickness measurements could also be integrated into forecasts issued for navigation and sea ice conditions.