When looking at a glacier from an airplane window, it may just look like one big white surface. The scientists who fly over the ice with lidar see a complex, layered world full of texture, hidden structure, and clues about how our planet is changing.
How It Works: Lidar
The tool at the center of this is lidar. The idea is simple: scientists mount a laser on a plane, the laser shoots pulses of light down toward the ground, and when the light hits something, it bounces back. By timing how long it takes for the light to return, they can calculate exactly how far away that surface is.
Do this millions of times, flying over a landscape, and scientists can build a detailed 3D map of the ground. It works beautifully on bare ground, on forests, and on city streets. But when the ground is made of ice, things get a lot more complicated.
The Big Surprise: Ice Isn’t Opaque
Here’s what may surprise people: ice is partly see-through to laser light. If a laser shines on a rock, the light bounces off the surface and comes right back. If that same laser shines on ice, some of the light bounces off the top, but some of it passes through the surface and travels into the ice before bouncing back.
This means a single laser pulse can produce more than one echo—one from the surface, one from a layer inside the ice, and maybe even one from the bottom. For scientists trying to map the surface of a glacier, ‘Which echo is the real surface? ‘can be a problem. It’s like shouting into a canyon and hearing three echoes come back. If you don’t know which one bounced off the nearest wall, you can’t tell how far away the wall actually is.
The fact that ice lets light in instead of just reflecting it is actually central to how we measure sea-level rise.
Why This Matters: Measuring Ice That’s Disappearing
In places like Greenland and Antarctica, scientists fly over the ice year after year, taking measurements with lidar. If the ice surface is getting lower, the glacier is thinning. If it’s thinning, that mass is becoming meltwater—and meltwater raises sea levels.
If the laser sometimes penetrates into the ice before bouncing back, the measurement will say the surface is lower than it really is. It might look like the ice has thinned by a few inches, when actually it hasn’t changed at all—the laser just saw something a little deeper and got confused.
A few inches of error may seem insignificant, but when measuring thousands of miles of ice year after year, these small inaccuracies accumulate. When the difference between “stable” and “melting fast” is only a few inches per year, accuracy is crucial; a few inches per year, getting it right is everything.
Layers Inside the Ice: An Unexpected Bonus
The same property that makes lidar tricky on ice also makes it unexpectedly powerful. The laser can penetrate below the surface, and it can sometimes detect layers within the ice.
Every year, new snow falls on top and gets compressed into ice, building up new layers year after year. Sometimes a specific event, like ash from a volcanic eruption, gets buried in a single layer, marking that year precisely. All of this creates a record, trapped in the ice. Lidar can trace some of these layers across huge stretches of ice, connecting individual drill sites and painting a picture of how the ice has changed over time.
Different Kinds of Ice, Different Kinds of Problems
Not all ice is the same. Snow sitting on top of a glacier scatters laser light in all directions, making it hard to get a clean reading. When ice melts in the summer and water pools on the surface, those meltwater ponds act like mirrors and can bounce so much light back that the sensor gets overwhelmed.
Over the ocean, sea ice shifts and cracks and piles up into ridges. The roughness of the ice tells scientists how old it is, but thickness from above is a much harder problem.
For all its power, lidar has real limits. It usually can’t see all the way through a thick glacier to the rock underneath. For that, scientists use radar, which uses radio waves and can reach the bottom of an ice sheet a mile or more thick.
It also needs clear air. Clouds, fog, and blowing snow scatter the laser beam and can make a flight useless. In the Arctic and Antarctic, good flying weather is rare and getting rarer as the climate warms.
The best science comes from flying multiple sensors at once and combining everything into one picture, because each tool sees something the others can’t.
Why We Should Care
The question of how quickly the world’s ice is melting is one of the most consequential questions in climate science. Every fraction of an inch of ice lost from Greenland or Antarctica ends up in the ocean, eventually amounting to feet of sea-level rise—enough to reshape coastlines and displace millions of people.
The accuracy of those projections depends on measurements, and the accuracy of those measurements depends on understanding what our instruments actually see. When a laser looks at ice, it doesn’t see a simple white surface. It sees a layered, shifting, half-transparent world. Only by putting every tool together do scientists get close to the truth. Learning to read that world correctly is one of the quiet, difficult, absolutely essential tasks of our time.
