Laser scanners (LIDAR) create high resolution digital point clouds by measuring the time it takes for a transmitted laser signal to be reflected from the sensor, to an object, and back to the sensor. A laser scanner is an active sensor; it produces its own signal and eliminates the need to rely on ambient lighting to produce usable data. This is a critical difference to the Structure from Motion (SfM) method.
The biggest advantage of aerial laser scanning is the ability of this laser signal to ‘penetrate’ vegetation and tree canopies. Canopy penetration is a common term used in remote sensing, though it is not entirely accurate. This sensing technology cannot see though a leaf, but it can find a gap between leaves and return a signal based on its reflection through that gap. Aerial laser scanning offers the capability to create a 3D point cloud which quickly maps significantly larger areas than can be assessed with terrestrial methods. The primary deterrent to laser scanning is its cost. When cost is a concern, structure from motion can be an acceptable alternative.
LIDAR sensor packages made specifically for sUAS applications cost $40,000-$200,000. The core influences on a LIDAR sensor package costs are the accuracy of the global positioning system / inertial measurement unit (GPS/IMU) and the capability of the LIDAR head. The GPS/IMU is the critical component to reference and scale the point cloud. Without it, the point cloud would just be an arbitrary collection of points. With it, valuable measurements can be made from the point cloud to a certain degree of accuracy.
The GPS determines the points’ real-world location and for a LIDAR sensor package, this GPS is corrected by either RTK or PPK methods. Next, the IMU determines the orientation of the LIDAR head while it is collecting points. This is critical to accurately resolve the point cloud. An entry-level IMU has an accuracy of plus/minus 5cm. An advanced IMU will increase this accuracy to plus/minus 3cm. This gain in two centimeters increases the cost of the sensor by 50%. Detailed next is the LIDAR head which is the final cost-driving component of a sUAS LIDAR sensor package.
A common LIDAR head used in sUAS LIDAR packages is the Velodyne VLP-16 (http://velodynelidar.com/vlp-16.html). This LIDAR head is purpose-built for autonomous vehicle navigation. Due to the increasing demand of this market, these LIDAR heads are continuously improving and decreasing in cost. Many companies have taken advantage of the VLP-16’s relatively low cost and small size to build sUAS LIDAR sensor packages. Increasing the capability of a LIDAR head is most directly related to increasing the scan rate of the head. Given the same flight profile, a more expensive LIDAR head will typically produce a denser point cloud over a lower cost LIDAR head. However, an increase in LIDAR head capability can increase the cost by 50%-100%.
Listed below are examples of a few sUAS LIDAR sensor package providers:
Geodetics: https://geodetics.com/product/geo-mms/
Emensent Autonomy: https://www.emesent.io/
Phoenix LiDAR Systems: https://www.phoenixlidar.com/lidar-products/
LiDAR USA: https://www.lidarusa.com/
YellowScan: http://www.yellowscan.fr/products/yellowscan-surveyor
BoE Systems: http://www.boesystems.com/
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