Lidar day!

Today is (informally) lidar day! You might not have the day off work, your kids might not bring home art projects featuring lidar, and it’s probably not possible to have a cake emblazoned with a point cloud, but lidar is taking center stage in science throughout the world and we want to celebrate!

Wave goodbye to the moon—lidar tells us it’s receding by inches per year.

But what is it? Lidar—Light Detection and Ranging, or a combination of ‘laser’ and ‘radar’—has been around since the 1960’s when folks first used lasers to measure the distance between objects. During the Apollo missions, in addition to collecting great moon rocks for geologists to study, the astronauts also installed reflectors that scientists use with lidar to measure how quickly the moon is moving away from the earth (~3.8 cm/yr it turns out, slowing our orbit about 2 seconds per century).

point cloud
‘Point cloud’ data of both vegetation and the ground surface. From UC Division of Agriculture and Natural Resources Green Blog (click for link)

In the past two decades, people have developed ways to mount the lidar equipment to a light plane and take millions of data points as the plane flies over the ground surface. Because of how fast data is collected, and the specific frequencies of light used, scientists are able to measure the elevation of both the vegetation and the bare earth. These new techniques allow unprecedented levels of accuracy (less than ~5 cm) in the elevation of the Earth’s surface—typically a tricky thing to really pin down.

This has led to an ‘elevation revolution’ for earth scientists, surveyors, land planners, farmers, anyone who thinks about the Earth or needs data about its elevation. Even the military.

One of the biggest uses in earth science is the identification of geologic features in vegetated regions. Sure enough, it’s easy (for a geologist) to see fault scarps, old landslides, and other features in a desert region, but throw the Olympic rainforest on top and a healthy dose of soil and moss, and natural hazards become more difficult to identify.

comparison photo
The three images above illustrate the differences between lidar (center) and the existing, statewide topographic dataset from shuttle radar (right) at the same location as the aerial image (left). The dense tree canopy in portions of the aerial image show the ability of lidar lasers to pass between tree leaves and needles to accurately measure the ground. Note that the lidar image captures the road system in the lower third of the image, also evident in the aerial image.

This is where lidar comes in—by penetrating the dense forest canopy and showing (in detail) the shape of the ground surface, it’s as if we lifted up the forest by the nape of its neck and once-hidden geologic structures are revealed.

For planning—the lidar topography clearly shows roads and other man-made features.

Okay, so maybe waxing poetic about geology doesn’t stir your emotions, but lots of other people are also using lidar: Foresters use it to monitor the height and volume of timber from year to year and can determine optimal times for harvest; farmers can use it to determine crop yields before harvest or where they should apply more fertilizer; land-use planners can develop 3D models of their cities; your new car that automatically slows down is using lidar to keep you safe; the military can use lidar surveys to detect recent land disturbances (read: roadside ordinances) and stop convoys before they reach danger.

Floodplains—subtle landforms can be identified by lidar that are not visible with other methods.

So raise your mouse, pint glass, coffee mug, or whatever nerdy object you’re holding to lidar—keep it up, smart people.