How to measure snow from space

Kiowa Peak, seen from the University of Colorado Institute of Arctic and Alpine Research’s Tundra Lab, some 3,810m above Boulder, Colorado. To unlock the capabilities of the new Nisar satellite, scientists had a key task: to measure the depth of snowpack atop a mountain at the exact moment the satellite passed overhead. — Nina Riggio/The New York Times

AT 4.30am on a recent Wednesday, three scientists arose from fitful sleep in a chilly research lab in the Colorado mountains, 3,500m above sea level.

They drank some grainy coffee, strap­ped into their skis and headed out into the moonlight, dragging a sled loaded with gear.