Unmanned aerial vehicles (UAV), or drones, make the acquisition of geo-referenced aerial images more efficient than ever. In addition to cost savings, companies implementing survey-grade drones also benefit by reducing risks to survey teams, especially along congested transport routes and in unstable environments like those often found around mines.
Accuracy down to 1-2 inches is possible, without the need for ground control points. Survey-grade drones are typically capable of receiving in-flight data corrections from a base operator for further refinement.
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Data Capture via Drone
Depending upon the application, either high-resolution cameras or lasers are deployed to capture essential data. Once the ground sampling distance is identified, the flight altitude of the drone is set automatically. Calculations define flight lines and where each image is to be captured. The landing zone is also pre-defined to bring the autonomous flight to a safe conclusion. Specialized flight control software makes it possible to monitor progress make any necessary flight plan alterations.
The process of taking measurements from photographs is called photogrammetry. Using appropriate software, images of land masses are converted into maps, 3D models or drawings. In aerial UAV photogrammetry, a drone captures overlapping images using waypoint navigation technology, which provides the precise flight path essential in this type of imaging. Specialized software integrates the overlapping images into one. Further processing converts the image into the desired map of 3D model.
LiDAR sensors use lasers for 3D mapping by bouncing extremely focused beams of light off of real-world objects like land masses. LiDAR stands for Light Detection and Ranging. Lasers quickly and efficiently measure variable distances such as from a drone to the earth below. In the past, laser arrays were mounted on helicopters, planes or satellites to collect required surveying and mapping data.
Now, drone technology makes this type data gathering less costly and more precise. As a LiDAR-equipped drone makes precise passes over selected terrain, tens or hundreds of millions of data points are gathered. On the ground, software filters out vegetation data to allow for precision terrain mapping. Ultimately, impressive 3D topographic mapping with resolutions down to 1-3 inches per pixel is possible.
When drones are deployed to survey terrain, an onboard SD card typically stores images and flight log information, and images are automatically geo-tagged. A quality report can verify the integrity of the coverage.
Choosing the Right Drone
Both quadcopters and fixed wing UAVs are used for aerial mapping and surveying. So-called vertical takeoff and landing (VTOL) drones combine the increased payload capacity and greater range of fixed wing drones with the exceptional agility of quadcopters. VTOL drones have been used in the military and for delivering medical supplies in challenging environments.
Recently, researchers at the Delft University of Technology released a prototype UAV which combines the strengths of both technologies. As the prototype VTOL drone reaches its desired height, the propeller shifts to face forward so that speeds of up to 66 mph are possible. The 10,000 MaH battery provides up to 60 minutes per charge. The 8.8-pound device uses inertial measurement unit (IMU) and GPS to track its position. It also includes obstacle avoidance technology.
New Technology Meets Ancient Architecture
The use of LiDAR sensors is ideal in settings where dense vegetation would ordinarily interfere with camera-based mapping of the underlying land mass. LiDAR’s capacity to “see” through dense forest is dramatically illustrated when archeologists used a laser-based system to locate and subsequently map areas just outside the temple walls of Angkor Wat in Cambodia.
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