Mighty backpack captures millions of topographical data points in minutes

Surveyors have been measuring and documenting the topography of the Earth for thousands of years. Though the instruments have evolved from the early days of rope stretchers to modern total stations, it’s been challenging to collect accurate data efficiently when surveying heavily wooded areas, until now. A team of Purdue researchers is revolutionizing traditional ground surveying methods with a new technology that maps millions of elevation points in mere minutes simply by walking around the area wearing a backpack.

“We’ve developed a backpack system equipped with GPS and inertial navigation systems as well as LiDAR sensing,” said Ayman Habib, the Thomas A. Page Professor of Civil Engineering. “The LiDAR system sends more than one quarter million pulses per second. Each one of these pulses derives an XYZ coordinate. The traditional total station and digital level surveying method captures a few hundred points a day in wooded areas. Using this new technology, millions of points are captured within a few minutes.”

The team has tested the new techniques at Ross Camp — a site 10 miles southwest of campus purchased by David Ross (BSME 1893) in 1926 to provide civil engineering students a training camp to practice the latest surveying technology. By Indiana standards, the site has significant vertical relief with some valleys more than 100 feet deep and vertical slopes of more than 35%. This rugged terrain has been used to compare traditional surveying methods against the LiDAR-equipped backpack. It took a team of four about seven hours to capture 140 points using two total stations. A backpack unit mapped the same area in 15 minutes.

Traditional surveying techniques will yield more accurate results when surveying solid surfaces, however for areas with soft terrain, such as forests and shorelines, the backpack method measures within an inch of accuracy. And its capabilities will have impact far beyond the construction industry.

“This technology has multiple applications,” Habib said. “It can be used to capture the biometrics of trees growing in a forest, map crops in a field, monitor erosion that could lead to landslides or evaluate the conditions of a shoreline. Some of this information can be captured through manned aircraft systems but that’s an expensive undertaking and therefore only performed on an annual or biennial basis. This technology enables scientists to gather data at a higher frequency which is essential to develop timely mitigation measures.”

Habib doesn’t see his technology replacing traditional ground surveying methods such as total stations, but rather complementing their use. Total stations may still be the preferred method for mapping solid surfaces, but the advanced technology of the LiDAR backpack empowers surveyors with greater capabilities for about twice the cost of a total station.

“One area of focus is how to harness the developments in sensor technology to give the user community the ability to use these technologies at an affordable price while delivering the level of accuracy they would get from traditional techniques, if not better,” Habib said.

Darcy Bullock, Lyles Family Professor of Civil Engineering, collaborates with Habib on the project and joined him for many of the backpack test runs. As the director of the Joint Transportation Research Program at Purdue, Bullock said he’s excited about the impact Habib’s technology will have on the transportation sector.

“Anytime a road is built near woods or wetlands, the entire area needs to be topographically mapped before construction,” Bullock said. “Accurate mapping is critical to estimate the cost of removing vegetative matter such as stumps, roots, buried logs and other debris to make way for the new road. This new technology will reduce labor, improve the quality of the data and increase safety for surveyors. It’s difficult work to haul around traditional equipment, crawling up steep slopes and over rugged terrain to mark every tree and boulder. The ability to accurately map the topography of these areas just by walking around with a backpack, it’s an absolute game-changer.”