In a state where nearly 80 percent of the land is covered in forests, mapping the ground surface can be a complex but critical endeavor. The Vermont Geological Survey, part of the Vermont Department of Environmental Conservation, conducts research and mapping relating to the geology and topography of the state and has recently started using LiDAR technology to map the world beneath our feet.
Most Americans hadn’t heard of LiDAR until 1971 when the Apollo 15 mission used it to map the surface of the moon. Since then, LiDAR has been used for everything from predicting earthquakes to mapping ancient Mayan ruins covered in thick rainforest. Today, it’s being explored as a technology for autonomous cars to identify the objects around the vehicle.
LiDAR, or Light Detection and Ranging, allows scientists to use sensors to see and map the bare Earth below vegetation. LiDAR relies on lasers invisible to the human eye to measure the elevation of the ground, forests and buildings by measuring the amount of time it takes for a beam of light to reach the object below and return to the sensor. It’s like sonar that uses sound waves to map things, but LiDAR relies on light instead.
In Vermont, LiDAR data is collected via stationary sensors or sensors connected to airplanes. Planes gather LiDAR data with a sensor that emits beams of light that scan side to side to gather information from the earth below.
For the purpose of studying Vermont’s landscape, the airborne LiDAR provides incredible detail over large areas. Geologists at the Vermont Geological Survey use Digital Elevation or Digital Terrain Models to gather land-surface elevation information void of vegetation and buildings. Geologists use these elevation models in combination with fieldwork to map glacial landforms, bedrock structure, landslides, and many other geologic features preserved on Vermont’s landscape.
One benefit of LiDAR sensors and data post-processing is the ability to extract land-surface elevation information in densely vegetated areas. This allows geologists to interpret the size and shape of landforms that otherwise would be difficult to see. Many features, such as ancient glacial lake shorelines, can be easily hidden from view by vegetation.
The high-resolution LiDAR elevation data is a tremendous dataset that the Vermont Geological Survey incorporates into many mapping projects. Utilizing this dataset allows for more detailed and accurate characterization of Vermont’s geology. To find recent publications that incorporated interpretation of LiDAR data visit (https://dec.vermont.gov/geological-survey/publication-gis/ofr)
Colin Dowey works for the Vermont Geological Survey in the Vermont Department of Environmental Conservation.