CRREL researchers test new modular LiDAR tower, sensors

The U.S. Army Engineer Research and Development Center's Cold Regions Research and Engineering Laboratory's (CRREL) Remote Sensing Geographic Information System Center of Expertise (RSGIS CX) is testing a newly engineered automated terrestrial laser scanning system (A-TLS) in Alaska.

The system will help determine how underground permafrost changes the landscapes above by capturing precise lidar laser scans that can detect any gradual caving or sinking of the surface area as a means of assessing and validating satellite-based assets for continuous monitoring of permafrost environments globally.

"The A-TLS is designed to capture high-resolution 3D data from multiple laser scanners for a specific focus area," said Adam LeWinter, a CRREL research physical scientist and lidar group team lead. "Specifically, the system was installed at our permafrost study site outside of Fairbanks, Alaska, in an effort to capture permafrost subsidence over the course of an Arctic summer and fall season."

LeWinter says the system was sent to the CRREL Fairbanks Office and installed at the Husky Drop Zone on Eielson Air Force Base by CRREL personnel during the week of May 16t. It will capture 3D scans and imagery every six hours during the summer and fall seasons. The data will be analyzed for surface change in an effort to measure and characterize permafrost subsidence.

The A-TLS has been installed on a 12-foot-tall tower affixed with multiple lidar laser scanners, meteorological sensors and solar panels. The tower, the components used to mount the electronics inside and outside the tower and newly designed Pivoxes - which are a combination of time-lapse cameras and low-cost lidar sensors - were all designed and built by CRREL.

At the heart of the A-TLS, a computer allows for onsite data processing each day, converting the raw lidar point clouds into georeferenced, compressed files. This data can then be reviewed by the research team without the need to physically visit the site and allows the team to remotely conduct any necessary configuration changes as they assess the performance of the sensors. With this capability, the team was able to refine the system operations remotely during the first few days of operation in Alaska.

Another aspect of the project is to establish the effectiveness of the Pivoxes and determine if they can be an inexpensive replacement for in-situ sensors requiring substantial infrastructure, such as pressure transducers used in measuring water levels in rivers and streams.

"A pressure transducer requires a well tube as well as annual calibrations," said Aaron Kehl, a CRREL mechanical engineer. "Installing a well tube in a river, or near a dam, is difficult and requires significant labor when done correctly and often, is not feasible in remote locations."

"It's another means of monitoring the rate at which permafrost is melting or expanding as well as what that means for the active soil layer," he continued.

Kehl says that depending on how well a Pivox establishes measurements of a target surface - whether it be permafrost soil or river water level - it could be used in lieu of a pressure transducer. It can also be used to monitor ice jams near infrastructure such as bridges. Through the use of a Pivox, the growth and speed of ice jams can be monitored to preserve the infrastructure as well as predict dangers to nearby towns.

While the Pivox system is configured to operate in tandem with the larger A-TLS control, RSGIS CX has developed standalone Pivox systems that can be deployed with a significantly smaller footprint and power requirement. These standalone Pivoxes would be ideal for rapid deployment needs for emergent situations, such as when a river gauging system has been destroyed by wildfire or flood, or to monitor developing ice jam conditions over a short period of time.

Kehl and LeWinter both believe the tower and Pivoxes have the potential to assist the Army with their strategic plan of regaining Arctic dominance by helping to calibrate satellite-based measurements of permafrost subsidence, determine construction sites, help quantify ice melt, quantify rise in water levels and quantify the size and speed of glaciers, or ice-jams.

This round of testing both the lidar tower and the Pivoxes is scheduled to conclude in October of this year. After which, the tower will be disassembled and stored at CRREL-Fairbanks - and the data thoroughly analyzed -then set up in a different location in the remote plains of Alaska in the summer of 2023.

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