How Ants Inspired a New Way to Measure Snow With Space Lasers

Ants, as a group, are creatures of behavior. Whereas a person’s path isn’t sure, biologists who’ve spent quite a lot of time watching the habits of complete colonies can predict the typical time anybody ant may wander round underground earlier than resurfacing. That received NASA physicist Yongxiang Hu questioning if the identical predictability may be true of photons—particles of sunshine—touring by the snowpack. If that’s the case, that will let scientists use a laser pulsed from an orbiting satellite tv for pc to estimate snow depth—doubtlessly a robust new approach to monitor water provides and the well being of sea ice within the Arctic. 

NASA’s ICESat-2 satellite tv for pc is supplied with lidar, the identical number of laser system that self-driving automobiles use to construct 3D maps of their environment. This extraordinarily delicate instrument fires trillions upon trillions of photons on the Earth, then analyzes what bounces again to the satellite tv for pc. As a result of scientists know the pace of sunshine, they’ll use lidar to find out altitude: A photon that bounces off the highest of a mountain will take barely much less time to achieve ICESat-2 than a photon that bounces off a valley ground.

The identical factor occurs if you shoot lidar right into a snowbank. “We will measure that distance of every particular person photon touring contained in the snow,” says Hu, a researcher at NASA’s Langley Analysis Middle. Some photons may go tens or perhaps a hundred ft deep into the snowpack earlier than coming to the floor and heading again to the satellite tv for pc. (The photons penetrate the snow as a beam, as an alternative of spraying out laterally. Think about the best way a laser shot by a cloud of smoke appears like a single line.) This delay exposes the snow’s depth, similar to a photon bouncing off a valley takes a bit extra time to return to the lidar instrument than one bouncing off a mountaintop. 

A photon’s path will not be at all times easy. Simply as an ant wanders round its underground colony, a photon shot from an area laser takes a random route by the snow. A couple of will journey all the best way to the underlying soil and mirror off it earlier than they arrive again aboveground. Some bounce again halfway by, after hitting snow particles. “Most of them go inches within the snow and are available again,” says Hu. “However then there are quite a lot of them that go very deep, very lengthy distances trapped contained in the snow—bouncing forwards and backwards, forwards and backwards.” All that ricocheting round makes for noisy information.

However inside it, there’s a sample, simply as there may be in the best way teams of ants, within the mixture, transfer round a colony. Whereas every photon takes an erratic path, scientists can mathematically characterize the typical distance that every travels. The crew calculated that on common, a photon travels twice so far as the depth of the snow it’s shifting by. 

As soon as they’d that formulation, the crew may estimate snow depth everywhere in the planet utilizing international lidar information from ICESat-2. Then they in contrast these estimates to snow depth measurements of the identical areas taken by airplanes utilizing radar. (A 3rd choice is inserting particular poles into the snow.) “They examine very effectively,” says Hu of the strategies. “We’re very blissful that the idea labored.”