LIDAR

Lasers at the Lava Flow

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By Ali Sundermier

After hiking for an hour and a half into the lava desert of Kilauea, NASA geologists Brent Garry and Patrick Whelley crouched by an outcrop to set up a yellow tripod. Whelley opened a matching yellow suitcase, pulled out a small UFO-looking gadget and placed it on top of the tripod.

It seemed almost anticlimactic. For the few days before this dry run, the crew had been describing Garry and Whelley’s light detection and ranging instrument, or LIDAR, as a massive piece of equipment. Yet here they were setting up an innocuous little spaceship on top of a thin yellow tripod.

A few minutes later, Garry and Whelley made their way over to a different section of the field. They took out a thick, black tripod and began driving its daggered legs into the ground. Garry unpacked a large metal device from a black suitcase. Its head was identical to the one Whelley had attached to the yellow tripod but it had a long cylindrical body, giving it the appearance of a quadriplegic robot. This was the LIDAR.

The LIDAR is a beast of a machine. Weighing in at 50 pounds, it was the heaviest piece of equipment on the mission. Although the crew often shared equipment-lugging duties during the 14-kilometer treks through Kilauea, it was often Whelley who had to bear the burden of the LIDAR.

Meet the team

Brent Garry

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Patrick Whelley

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Stephen Scheidt

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The LIDAR is essentially a giant laser pointer that delineates the shape of a landscape.

It quickly sends out laser pulses—a few hundred per second—and measures the two-way time it takes the laser pulses to leave the instrument, bounce off the earth and return to the detector. The smaller device that Garry and Whelley had installed first was a GPS that gave the LIDAR its exact positioning. Once the LIDAR was talking with the GPS and the environmental parameters were set, Garry and Whelley could begin scanning the area.

“It measures really accurately stuff that’s really hard to see from where you’re standing,” Whelley said. “The LIDAR tells us a lot about the landscape that we’re looking at that you’d otherwise ignore or wouldn’t notice.”

A large part of Theme 2 of RIS4E, Garry explained, involves comparing terrestrial geology to the geology of other planets. The LIDAR’s mission is to capture context. Scientists involved in this research project can use the data obtained by the LIDAR to pinpoint where all the other instruments have gone and get a very high-resolution, detailed topography of the features they’ve been looking at.

“You can’t always get that back at home. You can’t revisit it,” Garry said. “The LIDAR almost gives us a way to spatially revisit these outcrops that we were sampling or measuring and manipulate them in the office versus having to come back out in the field and remember what everything looked like.”

Garry and Whelley were looking for several different things when they brought the LIDAR to Hawaii. For one, they were trying to determine how useful this sort of instrument would be to an astronaut exploring the terrain of another planetary body during an extra-vehicular activity, or EVA.

“We can simulate using a LIDAR camera system to measure topography on the surface of another planet and figure out how that information would inform an astronaut in sampling,” Whelley said. “It’s a really useful tool for picking out rough surfaces or slopes that would be dangerous for an astronaut to walk on.”

The LIDAR can also give some spatial context to the EVAs, a luxury that wasn’t possible in the Apollo days. Back then, scientists and astronauts had to work with just a 2D map of the areas they explored, captured with a camera. With the LIDAR, they can actually see in 3D where samples are collected.

The LIDAR they used for this mission will most likely be too big for astronauts in space, so scientists at NASA Goddard Space Flight Center are working on a smaller, lighter and more energy-efficient version.

“We are seeing the limitations of what we have available to us with the commercial off-the-shelf instrument to drive the design of what we need to build for a specific mission in the future,” Garry said.

Beyond determining the utility and limitations of the LIDAR, Garry and Whelley were making use of their time on the Mars-like landscape of Kilauea for pure science. At the volcano’s 1974 lava flow, they were looking at a section that had banked up against one of the cliff faces, or scarps, and formed a giant lava pond. Garry and Whelley were interested in capturing the remnants of the lava pond: how high it was and how it was related to the surrounding topography as well as the older, pre-flow topography.

They were also investigating one of the lava channels in the area, trying to use the LIDAR to determine differences in roughness between the types of lava flows and see if they could figure out what the textures look like. By simulating this sort of scan, they could see if it was possible to scan lava flows that have been buried on Mars and determine the type of lava flow based on features picked up by the LIDAR.

In the field, Garry and Whelley typically did several scans of an area, each one taking from six to 15 minutes. From that they could then layer the scans on top of each other to create a much broader digital terrain model of the surface of the lava flows they were looking at.

As the LIDAR began slowly turning to survey the landscape for one if its long-direction scans, Garry and Whelley ducked down to eat some lunch out of the instrument’s line of sight. Whelley peeled open a big, refreshing can of protein-packed sardines. Garry, whose back had been turned to Whelley, was suddenly assaulted by the smell of fish, the scent expanding in the 85-degree heat.

“We couldn’t move because of the LIDAR. I just had to sit there, downwind of sardines, for ten minutes,” Garry said later. “It smelled like we were working at the aquarium.”

But that’s the price they pay for accuracy. Back at the village of cottages where the team was staying, Garry scrolled through the sets of images they had gathered on the mission.

“This scan is from the first day, the dry run day,” he explained. “The black streaks, or data shadows, are where people are in the way. You can fly in a little, rotate, zoom in, and begin to pick up the forms and textures of the lava flow. You start seeing people, trees, shrubbery.” He began pointing out different members of the crew who had been captured in the scan.

The image Garry was looking at is called a point cloud, because it’s composed of thousands and thousands of little points that create a 3D image from afar. Garry described the process of creating these images as “connecting the dots.” This particular scan was colorized by height to show the different elevations. Garry explained that he can also colorize the scan by the intensity of the reflectance—how it reflects light—to show differences within a lava flow, such as an area where it’s cracked open, and even slight variations in texture.

These point clouds can help scientists like Garry and Whelley look at relationships within lava flows, allowing them to investigate features like lava pits and lava ponds. By looking at the 3D reconstructions that the LIDAR allows them to create, they can get a better understanding of topographical details of these features and how they form.

As the sun began to set on the last data-gathering day of the trip, Garry and Weller stared out across the ever-shifting lava flows. With their trusty LIDAR by their side, the two geologists appeared in their element, ready to gather data and tackle the mysteries of volcanic terrain.

“You can’t replicate this in a lab,” Garry said. “Here it’s the ground truth of what you’re trying to model in a laboratory. We have to come out here because nature has the ultimate answer key and we have to figure out the questions.”