A NASA satellite designed to precisely measure changes in the earth's ice sheets, glaciers, sea ice and vegetation has been launched into polar orbit from California.
A Delta 2 rocket carrying the ICESat-2 lifted off from Vandenberg Air Force Base at 6.02am local time on Saturday and headed over the Pacific Ocean.
NASA earth science division director Michael Freilich says the mission will advance knowledge of how the ice sheets of Greenland and Antarctica contribute to sea level rise.
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The melt from those ice sheets alone has raised global sea level by more than 1 millimetre a year recently, according to NASA.
The mission is a successor to the original Ice, Cloud and Land Elevation Satellite that operated from 2003 to 2009.
Measurements continued since then with airborne instruments.
ICESat-2 carries a single instrument, a laser altimeter that measures height by determining how long it takes photons to travel from the spacecraft to earth and back.
According to NASA, it will collect more than 250 times as many measurements as the first ICESat.
In addition to ice, the satellite's other measurements, such as the tops of trees, snow and river heights, may help with research into the amount of carbon stored in forests, and also with flood and drought planning and wildfire behaviour, among other uses.
