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Nasa radar


High-altitude flights over Alaska this summer are measuring how various types of summer ice respond to laser altimeters
Above the wild white yonder (Photo: Nasa)

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Nasa scientists took to the wing over Alaska today on one of a scheduled six flights that will map summertime ice.

The mission, set to wrap up on August 1, is not expected to contribute directly to this year’s ice measurements. Instead, it is hoped that the findings will allow scientists to put the finishing touches on the instruments of the ICESat-2 satellite.

Due to be launched in 2017, ICESat-2 – short for Ice, Cloud and land Elevation Satellite – will measure the earth’s elevation by using laser light. By firing burst of lasers, the satellite will be able to calculate the distance to the earth depending on how long it takes for the beams to bounce back.

But, because the surface the lasers bounce off plays a role in how they are reflected, detailed calculations must be made before the satellite can be launched.

“We need to give scientists data to enable them to develop algorithms that work during summer,” Thorsten Markus, ICESat-2’s project scientist at NASA’s Goddard Space Flight Centre, said in a statement. “All the algorithms need to be tested and in place by the time of launch. And one thing that was missing was ICESat-2-like data on the summer conditions.”

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The measurements will be made using a piece of equipment called MABEL – Multiple Altimeter Beam Experimental Lidar – from an altitude of 65,000 feet (or double the cruise altitude of commercial passenger jets).

The measurements MABEL takes will resemble those taken by ICESat-2’s lone piece of equipment – nicknamed ATLAS (short for Advanced Topographic Laser Altimeter System) – which earlier this year was reported to be suffering from delays.

While MABEL will collect data on sea ice and glaciers, as well as forests, lakes and open ocean, Nasa scientists are focusing on how the laser system interacts with melt ponds and bare ice.

Melt ponds – areas where snow has melted and the water run off and formed pools on icy surfaces – are of particular interest because the darker surface of the water absorbs more heat than lighter ice surfaces. Scientists worry that these pools and the heat they retain can accelerate the pace at which the surrounding ice melts. 

“The melt pond coverage may be an indicator of the ice coverage at the end of the summer,” said Ron Kwok, a senior research scientist at Nasa's Jet Propulsion Laboratory, said. “But we don’t have a lot of information about melt pond coverage over the Arctic.”

SEE RELATED: Thin ice getting thinner

Nasa says it might also be able to use melt ponds to indicate the age of ice, since deep ponds can only appear on older ice that has had the time to build up formations where water can well up. Ice that was formed in the previous winter is too flat to develop deep ponds.

Scientists are uncertain how the laser beams will react when they hit these ponds: some may be reflected off the surface, while others could be reflected off the ice below the water.

The data collected over the next few weeks, Kwok said, should provide Nasa with enough information to calibrate ICESat-2’s ATLAS sensor.