Improvements in airborne scanning technology boost productivity
Leica TerrainMapper meets the challenges of large area mapping.
Author: Linda Duffy
Increased demand for aerial LiDAR is being met with improved scanning features and functionality that produce denser point clouds over larger areas in less time. As an early adopter of scanning technology, Woolpert, the fastest-growing architecture, engineering and geospatial (AEG) firm in the US, has owned and operated every product in Leica Geosystems’ LiDAR series since the ALS40 was released in 2002. Woolpert purchased its first Leica TerrainMapper in early 2019 and has since acquired three more. Today, the TerrainMapper is Woolpert’s preferred technology for large area mapping and difficult terrain, including Department of Transportation (DOT) projects and federal programs such as the United States Geological Survey (USGS) 3D Elevation Program (3DEP).A colorized 3D point cloud image (top) can be compared to a bare-earth image (bottom) looking northwest on U.S 26 near Wind River Lake in Teton County, Wyo.
Demand for elevation data
Aerial LiDAR data is a valuable source of information for many applications, such as 3D urban modelling, infrastructure development, coastal and natural hazard monitoring, and environmental conservation. Efforts are underway to establish a current national LiDAR dataset, and there are numerous local and regional entities investing in LiDAR coverage as well.
Expectations for density and accuracy continue to rise to match the enhanced capabilities of LiDAR sensors. Incremental improvements in performance culminated in the release of the Leica TerrainMapper, a linear-mode sensor that allows very dense point clouds to be collected at a higher altitude, greatly reducing acquisition time.
“With large area mapping, efficiency really pays off,” says Joseph Seppi, vice president and geospatial sector leader at Woolpert. “Our projects can exceed 30,000 square miles, even 100,000 square miles, so the ability to fly at a higher altitude at a faster speed makes TerrainMapper an extremely efficient option.”
The TerrainMapper is capable of collecting LiDAR at flying heights between 300 metres (m) and 5,500 m and delivers USGS LiDAR Quality Level 0 (QL0) data at flying heights up to 2 kilometres (km). This outstanding level of efficiency is ideal for larger regional or national mapping projects where operating costs have a major impact on the frequency of updates.The contours of the landscape without trees blocking the view are shown in this bare-earth point cloud image looking north on U.S 26 near Brooks Lake Creek Falls in Teton County, Wyo.
Meeting and exceeding the specs
Every project has minimum data requirements depending on the intended application. For example, USGS QL1 data must be at least 8 points per square metre (ppsm) with a Root Mean Square Error (RMSE) not exceeding 10.0 centimetres (cm). Other criteria may include leaf-off, no snow, no standing water, and no rain. In temperate climates, deciduous trees and snow are obstacles. In tropical and subtropical climates, clouds and rain are often a problem. Due to challenging conditions in many geographic areas, efficient data collection during limited flying windows is crucial for getting the job done.
In 2019, the Wyoming Department of Transportation (WYDOT) contracted with Woolpert to map three landslide areas along a 10-mile stretch of the Continental Divide in northwest Wyoming, close to Yellowstone National Park. Woolpert collected LiDAR at 50 ppsm and colourised the point cloud with imagery collected simultaneously with the integrated Leica RCD30 aerial camera. The final digital terrain models (DTMs) and triangulated irregular network (TIN) models provided WYDOT with a baseline to determine the slide movement, volume and rate at which the earth is moving over time. WYDOT performed an independent check and compared over 120 individual point cloud elevations from field collected points. The average elevation difference of 3.6 cm exceeded the requested 5 cm vertical accuracy.
The TerrainMapper has also proven effective on linear utility projects and powerline rights-of-way and successfully measures sag on elevated power lines. Even while flying faster and higher than other sensors, the TerrainMapper returns the necessary point density for a variety of projects.
“In high relief terrain we achieve greater efficiency by flying higher without adjusting to as many different altitudes,” Seppi stated. “And for utility work, it is safer to fly at a high altitude far above the lines, with the added benefit of capturing more of the surrounding area.”
Woolpert also flew more than 10 USGS projects in various states in 2019 with the TerrainMapper. In states like Florida and Ohio, the large volume collection at high speeds was instrumental in completing mapping projects within one flying season, despite the weather conditions.
“The weather in some places can be challenging, leaving us with fewer days to work, so the high-volume collection capability of the TerrainMapper helps us finish the project quickly and maintain consistency,” Seppi continued. “Also, the point distribution, patterns and excellent intensity returns from this sensor are extremely beneficial for many feature extraction uses.”
This zoomed-in contour map shows features such as pavement, pipes, and a culvert near Wind River Lake.
Acquisition and processing integration
The post-processing workflow is another area where efficiency impacts overall project costs. Woolpert uses the Leica HxMap multi-sensor processing platform, which is designed to streamline the handling of TerrainMapper data. HxMap processes, calibrates, and registers LiDAR point clouds while simultaneously processing image sensor data and colourising the point cloud. With help from HxMap, Woolpert delivers fully processed classified point clouds that meet strict project specifications for accuracy and density.
“HxMap allows us to be more agile and adapt on the fly to changes,” says Seppi. “We can easily shift processing around to allocate HxMap resources from other projects when we have a critical deadline. HxMap is like a black box that automatically performs its work behind the scenes.”
Designed specifically to work with TerrainMapper data, HxMap leverages the advantages of the integrated scanner/camera system to generate all airborne data products within one single interface. HxMap offers embedded aerial triangulation and a solution for large oblique imaging projects, country-wide orthophoto projects, and large or small LiDAR projects.
The Wyoming Department of Transportation translated the lidar data provided by Woolpert into a variety of graphics, including a digital terrain model of the area near Wind River Lake.
The Leica TerrainMapper is the next generation of LiDAR sensors after the highly successful ALS80 series. The sensor system increases data collection rate versus flying height, improves flight planning, and achieves even point distribution. The enhanced productivity saves time and money, while the higher pulse rate, greater laser power and gateless technology contributes to higher point density.
“Leica Geosystems sensors just keep getting better,” Seppi says. “The performance jump to TerrainMapper from ALS80 was significant. We find the circular scan pattern has a lot of advantages, such as line-to-line calibration and adjustment for pitch. Flying higher and faster boosts our efficiency 200-400%. Leica Geosystems products have been the backbone of our sensor fleet since 1989.”
Demand for 3D LiDAR data is on the rise, which makes timely acquisition and processing increasingly important. The tight integration of TerrainMapper with the HxMap workflow expedites the entire process, from data download to product generation, to support faster turnaround on every mapping project.