7 December 2015
Ben Shinabery (right), a land surveyor in Louisville, Ky., stands in Big Bat Cave with a volunteer and a lidar scanner sitting atop a tripod. Shinabery travels to Big Bat Cave once every 2 months to scan a new section of the cave. Credit: David Black
A compass, some measuring tape, a couple of waterproof notebooks, and a pencil or indelible pen: These are the bare minimum supplies a caver needs to create a map of a cave. While one person measures, sets compass headings, and calculates angles and true distances, another person slowly trails behind, making intricate hand-drawn sketches of the cave’s geological features.
These days, cavers also employ handheld instruments that use laser beams to determine heights and distances. This is how Dave Field, a retired geophysicist and avid caver who heads the Mid-Atlantic Karst Conservancy, maps caves in Pennsylvania. However, these small instruments don’t have the range needed to determine the size of large caverns where roofs and tunnel endings may be lost in darkness.
Several hundred miles away, in Breckenridge County, Ky., cave enthusiast and former state cartographer Ken Bailey, who is now the president of the Kentucky Karst Conservancy, deploys a much more powerful laser technology to map caves. The equipment, called a lidar terrestrial scanner, offers much greater range and data-gathering ability than hand-held devices.
Bailey has teamed up with Ben Shinabery, a land surveyor with access to a scanner, to create three-dimensional (3-D) cave maps of Big Bat Cave—the world’s 57th longest cave—near Custer, Ky. Unlike Field’s laser range finder, a lidar scanner pulses thousands of times per second, gathering thousands of data points per pulse. The data, when processed with powerful software, spit out a precise 3-D map of the cave, opening up whole worlds of information.
First Maps, Then Science
Although people have explored caves since there have been people, the quest for scientific insights from caves remains a challenge. Scientists who work in caves say that ways to map caves more thoroughly and accurately could have a major influence on how that quest goes.
“I tell many cavers that [they’re] the Lewis and Clarks” of cave science, said George Veni, a hydrogeologist and executive director of the National Cave and Karst Research Institute. “Without these maps, we can’t do the science in any effective manner.”
As a hydrogeologist, Veni looks at maps of caves that act as aquifers and can see how such caves function, right down to the permeability of the rocks, the structure, and the very plumbing of the terrain.
Mapping caves with the precision of lidar could also open up investigations to a wide range of scientists outside of hydrology, Veni said, from biologists studying bat populations, to archeologists studying ancient societies, to geomorphologists studying how caves form, change, and erode. Caves also offer a multitude of localized paleoclimate data, Veni said, which could be revealed by 3-D maps.
Lidar’s Ups and Downs
Lidar has already proven itself a boon to science beyond the confines of caves. In the last couple of decades, scientists have used it to study Earth’s surface and atmosphere and to investigate forests, ice sheets, mountains, and even coral reefs in high resolution.
Lidar works by shooting pulses of laser beams at a target, measuring how long it takes for the light to bounce back, and then calculating the distances. Some say that the technology’s name derives from “light radar” because the technology works like radar but uses pulses of light instead of radio waves. Others identify LIDAR as an acronym, probably for “light detection and ranging.”
In Pennsylvania, Dave Field relies on publicly available aerial lidar data of the state’s topography to find sinkholes that might lead him to caves. Since the data became available, he said, the rate of discovering sinkholes has gone up significantly.
“It’s been a real enlightenment just to see how much karst is out there,” Field said, using a term for any landscape built on rocks, such as limestone, that water slowly dissolves—a process that creates such features as sinkholes and caves.
Below ground is another matter. The equipment isn’t terribly portable, Veni said. Cave exploration often requires a person to squeeze through excruciatingly tight tunnels, navigate up and down sudden rises or drops, and sometimes even swim through water—with only 3 centimeters of breathing room underneath a tunnel’s roof.
“It’s a new tool, and, again, we’re taking it into an environment that is hostile to electronics,” Veni said.
Because the technology is so expensive—a good lidar scanner can cost over a hundred thousand dollars—not many scientists have been able to take advantage of this valuable tool, Field noted.
The Largest Caves
Andy Eavis, a self-described “cave fanatic” who has been exploring caves for more than 50 years and has mapped more than 500 kilometers of caves around the world, is currently using lidar technology to scan the world’s largest cave chambers. In preparation for the International Union of Speleology meeting in 2017, he and his team plan to produce 3-D-printed models of the vast caverns. The purpose, Eavis said, is to concretely define particular cave terminology like “passageway” or “chamber” because there is still some disagreement over what exactly these terms mean. For instance, how wide is a “passageway”? How high must the roof be to call an area a “chamber”?
Eavis and his team use a lidar scanner with a resolution of 1 centimeter and a range of up to 400 meters, which has suited their needs perfectly because one of the caves they scanned just last month—Cloud Ladder Hall in China—hosts a roof towering 365 meters (1197 feet).
“These roofs are bigger than any roofs man has ever made. Structurally, they shouldn’t really stay up, they should have fallen down a long time ago,” Eavis said.
In the past 2 years, Eavis and his team have mapped nine chambers in Malaysia, China, Spain, and France. Upcoming trips include visits to caves in Iran, Oman, Mexico, and Belize. A 3-D map produced by laser scanning of the Miao Room in China was recently documented in a National Geographic feature.
After Eavis and his team are finished with their multicave scanning project, he says they’ll sell the $150,000 scanner because they will have no more use for it.
Shinabery, the land surveyor, travels from Louisville, Ky., to Big Bat cave once every 2 months to scan another leg and is often accompanied by a team of volunteers—students looking for research experience, members of the community who want to explore the cave, or local scientists. The karst conservancy has already put together videos of the scanned portions of the cave. The green spheres that come and go in the video below are reference points set up by Shinabery. Likewise, the black boxes represent where the scanner was placed during each scan.
download mp4 video here .
Bailey hopes that creating 3-D maps of Big Bat Cave and other Kentucky caves might lead to more conservation efforts. Caves not only provide homes to living things, including bat colonies that are currently being decimated by white-nose syndrome, but also provide water to millions of people across the nation.
However, if people can’t see the caves, they might not care, Bailey said.
“We are protecting ourselves when we protect [caves],” he continued. “To be able to show people who will never go there why it’s worth saving is what the lidar is for me.”
—JoAnna Wendel, Staff Writer
Citation: Wendel, J. (2015), Laser beams brighten prospects for cave science, Eos, 96, doi:10.1029/2015EO040995. Published on 7 December 2015.
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