A lightweight laser scanner for UAV-based applications

Abstract

Laser scanners are widely used for the 3D-measurement of large-scale infrastructure objects. For objects like bridges or special tunnels unmanned aerial vehicles (UAVs) are well suited mobile platforms for inspection. Laser scanners used in these scenarios must be lightweight and low in power consumption to maximize flight time. A laser scanner optimized for UAV-based applications was developed by the Fraunhofer Institute for Physical Measurement Techniques IPM. The system is based on the pulsed time-of-flight measurement technique. A 1550 nm pulse laser featuring a repetition rate of 1 MHz for high point density is used as a light source. The short pulse length of less than 1 ns allows for a precise detection of the reflected signal in the time domain. Beam deflection is done with a rotating 45° mirror as in typical profile scanners. To optimize for detection aperture and weight, a custom mirror was designed. A lightweight scanning motor with a maximum rotation frequency of 120 Hz was chosen. An optical deflection path was developed that allows for a full 360° scan without any shading. The housing is made from aluminium and carbon fibre to reduce weight. The prototype of the laser scanner has a total weight of 2.1 kg and a power consumption of less than 100 W. The laser scanner is eye-safe (laser class 1) which is especially important for UAV-based applications. Test measurements in an indoor facility show a measurement uncertainty (one standard deviation) of approximately 3 mm on a surface at 10 m distance. The system was also mounted on a drone for flights in a tunnel which resulted in dense point clouds with high precision confirming the laboratory tests. Regarding the measurement uncertainty there is still a large potential for improvement by optimizing the full waveform analysis. First tests indicate that a reduction of the uncertainty by one order of magnitude may be possible.