As a group, ants are creatures of habit. While an individual's path isn't certain, biologists who have spent a lot of time watching the behavior of entire colonies can predict the average time any one ant might wander around underground. Yongxiang Hu wondered if the same predictability could be found in light particles traveling through the snow. If that is the case, it would allow scientists to use a laser from a satellite to estimate snow depth.
NASA's ICESat-2 satellite is equipped with lidar, the same type of laser system that self-driving cars use to build 3D maps of their surroundings. The instrument fires trillions of photons at the Earth and then analyzes what goes back to the satellite. A photon that bounces off the top of a mountain will take less time to reach ICESat-2 than a photon that bounces off a valley floor.
When you shoot lidar into a snowbank, you can measure the distance each photon travels inside the snow. The photons might go deep into the snow before they come to the surface and head back to the satellite. The photons penetrate the snow as a beam. Imagine a laser shot through a cloud of smoke. It takes a bit more time to return to the lidar instrument than a photon bouncing off a valley.
A path is not always easy. A photon shot from a space laser takes a random route through the snow as an ant wanders around its underground colony. A few will travel all the way to the underlying soil and reflect off it before they come back aboveground. Some bounce back after hitting snow particles.
There is a pattern in the way groups of ants move around a colony. Scientists can represent the average distance that each photon travels with a mathematical representation. The team calculated that a photon travels twice as far as the depth of the snow it is moving through.
The team was able to estimate snow depth using global lidar data from ICESat-2. They compared the estimates to the snow depth measured by the airplanes. The methods compare well, Hu says.
All Rights Reserved © 2024
