LOS ANGELES • Nasa's most advanced space laser satellite blasted off yesterday on a mission to track ice loss around the world and improve forecasts of sea-level rise as the climate warms.
Cloaked in pre-dawn darkness, the US$1 billion (S$1.37 billion), half-tonne ICESat-2 launched aboard a Delta II rocket from Vandenberg Air Force base in California at 6.02am (9.02pm Singapore time).
"Three, two one, lift-off!" said a launch commentator on Nasa television. "Lifting ICESat-2 on a quest to explore the polar ice sheets of our constantly changing home planet."
The launch marks the first time in nearly a decade that Nasa has had a tool in orbit to measure ice sheet surface elevation across the globe.
The preceding mission, ICESat, launched in 2003 and ended in 2009. ICESat revealed that sea ice was thinning, and ice cover was disappearing from coastal areas in Greenland and Antarctica.
In the intervening nine years, an aircraft mission called Operation IceBridge, has flown over the Arctic and Antarctic, taking height measurements of the changing ice.
But a view from space - especially with the latest technology - should be far more precise.
The new laser will fire 10,000 times in one second, compared with the original ICESat, which fired 40 times a second.
Measurements will be taken every 0.7m along the satellite's path.
"The mission will gather enough data to estimate the annual elevation change in the Greenland and Antarctic ice sheets even if it's as slight as 4mm - the width of a No. 2 pencil," Nasa said in a statement.
Importantly, the laser will measure the slope and height of the ice, not just the area it covers.
"One of the things that we are trying to do is, one, characterise the change that is taking place within the ice, and this is going to greatly improve our understanding of that, especially over areas where we don't know how well it is changing right now," said Dr Tom Wagner, cryosphere programme scientist at Nasa, mentioning the deep interior of Antarctica as one such area of mystery.
The mission is meant to last three years but has enough fuel to continue for 10, if mission managers decide to extend its life.
The satellite's instrument, called the Advanced Topographic Laser Altimeter System, or Atlas, will also measure the heights of forests to determine the amount of vegetation in a region, as well as monitor other attributes of land surfaces, water and clouds. By precisely measuring the elevation of land ice, Atlas and ICESat-2 will help scientists develop a better sense of how much and how quickly that ice is melting in a warming world.
We already know that the melting that is taking place in the enormous storehouses of fresh water locked into the ice sheets of Greenland and Antarctica is increasing sea levels by 1mm a year, accounting for a third of the total rise. Other glaciers and ice caps account for another third, and the rest can be attributed to the fact that warming ocean water expands in volume.
A deeper and more precise understanding of the melting will lead to a better understanding of sea level rise. Measuring the height of that ice will also shed light on the effects of the fresh water on things like ocean currents.
Dr Tom Neumann, deputy project scientist for the new satellite, said it would provide "a phenomenal picture" of changes in the planet's ice sheets and water.
"It's going to enable science discoveries in the cryosphere and polar research for years to come," he said.
AGENCE FRANCE-PRESSE, NYTIMES