LIDAR - like radar with lightwaves

DW: Mr. Kiemle, what exactly is LiDAR?

Christoph Kiemle: LiDAR stands for Light Detection and Ranging. It's similar to radar, or radiowave detection and ranging, but it works with optical radiation rather than radio waves. It works with light, basically. You can use lasers to send out this light to discover properties of the atmosphere or the Earth surface.

We typically send a laser beam down to Earth from an airborne platform. That beam travels through the atmosphere and can measure particle matter, aerosol in the atmosphere for example. It can detect clouds, it could travel down to the surface when there are no clouds, and it gives us profiles of atmospheric properties. We can detect and derive a lot of information from these measurements that help advance science.

We can also measure trace gases in the atmosphere. These are gases that are present in very small amounts in the atmosphere. This is an interesting new perspective and important for the future because a lot of greenhouse gases can be measured with this principle, like methane and CO2.

At your institute at the DLR you have an airplane equipped with LiDAR scanners, the Dassault Falcon. What do you do with that?

The advantages of an aircraft of course are that you can take it virtually anywhere and you can join other research groups. We have done a lot of such international campaigns in the past decades. Because it's a moving platform you can scan a certain area quickly.

Researchers have recently used LiDAR this way to discover a lost Mayan city in Guatemala. How did that work?

LiDAR's laser beam has a very small focus spot, or field of view. This enables it to occasionally penetrate the forest canopy, even though tropical forests are of very, very dense vegetation.

With a LiDAR system that is airborne, and if you have a laser with a high repetition frequency that emits a lot of shots per second, you can make your measurement curtain quite dense. So the probability that you will hit a hole in the canopy with your laser beam is a higher, and you'll occasionally get signals reflected back from [structures on] the surface.

What are some practical applications for LiDAR, aside from discovering ancient, long-lost cities?

There are two basic applications. There are LiDAR scanners that simply scan the Earth surface. They can detect irregularities in surface elevation, like in the Mayan case. Urban planning or agriculture forestry also use these kinds of lasers.

And we use LiDAR to learn more about atmospheric properties. That advances climate research and could improve weather forecasts.

What could future uses of LiDAR be?

There are plans for self-driving cars: Instead of radar, you could use LiDAR to calculate distances to other cars. Using optical radiation for this is more precise than radar.

Another field is space applications. The European Space Agency will launch the ADM - the Atmospheric Dynamics Mission - this year. There will be satellites with LiDAR on board to improve weather forecasts.

Wind speed is a main ingredient for weather systems and it can be derived from motions of clouds already visible in satellite images. But sometimes you have no clouds and therefore you have no motion vectors as they say. LiDAR can measure atmospheric changes in these cloud gaps. This mission is expected to bring us significantly advanced weather forecasts.

Christoph Kiemle is a research associate at the German Aerospace Center's Institute for Atmospheric Physics.