Kimball Erdman and Malcolm Williamson have worked together on many projects, but never one in an alien land.
That’s how Erdman described the environment of Carlsbad Cavern in New Mexico, the centerpiece of Carlsbad Caverns National Park where a team of University of Arkansas researchers assembled to digitally map and write an exhaustive report on the dimensions, history and condition of one of the country’s best-known caves.
Williamson’s team is using a laser scanner to produce a three-dimensional map of the expansive cavern’s public trail areas.
Erdman will then incorporate the digital map into the Cultural Landscape Inventory he is writing for the National Park Service, which operates the park. The formation includes more than 119 caves, including Carlsbad Cavern itself, the best-known.
“As you can imagine, the cavern is a very complex landscape,” said Erdman, an associate professor in the university’s Department of Landscape Architecture.
“I’m sure it’s the most complex and alien of anything I’ve ever worked on.”
Williamson, research associate with the university’s Center for Advanced Spatial Technologies (CAST), said he is using a scanner that uses light detection and ranging technology (LiDAR) to produce a three-dimensional map of the cavern.
The scanner, in layman’s terms, sends out a pulsed laser and then collects the measurements by reflection; Williamson said the $123,000 device can collect up to 1 million data points a second.
Williamson and a colleague spent 16 days in the cavern in late January and early February before returning to what he believes is the last data collection trip last week.
In the first 16 days of scans, working mostly in the evenings when the cavern was empty of people, Williamson recorded data from 736 collection points and compiled more than 935 gigabytes of information.
The scanner is set up on a tripod or a solid surface, depending on the topography of each collection point, and it rotates 360 degrees for about five minutes.
During the revolution, the scanner collects more than 6 billion bits of data with full coverage vertically and nearly 300 degrees horizontally, with accuracy as close as 2 millimeters on objects as far as 50 meters away.
The scans can be combined, and Williamson is quick to show a virtual reality-like tour of the cavern using the aggregate scans.
“This is a monstrous data set,” Williamson said. “That’s a single file. It will be over a terabyte by the time we’re done.”
‘Little Bit of Art’
Williamson has digitally mapped structures such as the Great Pyramid of Giza, London’s St. Paul’s Cathedral and a stone building in Petra, Jordan. The CAST team had also scanned a portion of Blanchard Springs Caverns in Stone County near Mountain View.
But Carlsbad Cavern is a different beast altogether, and it required learning and adjustments on the fly. Williamson said the actual scanning work in the cave was pretty mundane.
The scanning process is straightforward: The team sets up the scanner and circles behind it for five minutes so as not to appear in the data captures. After five minutes, the team moves the scanner to the next collection point and repeats the process.
Some data points are close to each other because cave or manmade formations can block the scanner from getting a full picture. The research team is sticking to the 3½ miles of man-made trails in the cavern and trying to shoot from the human perspective.
“It’s a little bit of art,” Williamson said. “If you’re on the trail, you are going to see pretty much everything that is visible from the trail. We document each position; we take a picture at each position; we record a description of each position.
“The great thing about this — the work itself is pretty dull — but you’re spending hours with nothing more to do than look around the cave while you’re waiting for the scan to finish. You get to see some amazing things in the cave that most people don’t get to see because they’re not there long enough to spot them.”
Williamson said the team was all alone in the cavern at night with just a walkie-talkie and a bag full of flashlights. One exception was when they scanned during daytime hours from a trail no longer in use, and in many of the scans the apparition-like bodies of tourists appear.
In several scans, a disembodied head seems to float above the trail. Williamson sheepishly admits that it’s his head, showing up whenever he was too slow or distracted to move out of the scan’s view.
Erdman said the laser scanning of the cavern allows achieving something that seems practically impossible. The scope of the cavern — the Great Room is more than 8 acres — would overwhelm conventional measurement techniques. Plus, as expected in a limestone cavern, more stalactites and stalagmites than a normal person would want to count.
Carlsbad Cavern, discovered in the 1890s, is far from pristine; it has become a tourist attraction with approximately 500,000 annual visitors. Early in its tourism history, a lunchroom was built into the cavern, 3½ miles of concrete trails were installed with lights and seating, and elevators were built when it opened as a park in 1932.
The CLI is an attempt to document the exact condition of the cavern for the National Park Service, which is paying the university team $182,400 for the digital map and the CLI report, the first the NPS will have done on Carlsbad. Erdman said the CLI should take two years to complete, will be hundreds of pages long and will be boring when compared to an interactive digital map of the cavern.
“Mapping is the sexy thing,” Erdman said. “The real product is going to be a dry report. But that is going to be the principal value.
“It was felt that a digital scan of the cavern would be the best way to capture and describe the landscape. It would be impossible to do hand measurements of the cavern. The digital scan will allow us to create the report. It’s not the only piece but it’s an important piece for the project.”
Erdman said the project is important, showing the current status of the cavern and the effects that more than 100 years of human interaction have wrought.
“It’s really amazing to get to work on this project,” Erdman said. “It’s really different than any landscape I’ve ever worked on. This report helps all those involved, including the National Park Service, [establish] that this is a landscape, and it does have the same values and concerns and problems that a typical above-ground landscape has.
“This is a cultural landscape. That awareness is one of the largest benefits to all involved.”