Dissipation of heat can be a major challenge when applying sensor systems outdoors under varying environmental conditions. Typically, complex software and knowledge is needed to optimize thermal management. In this paper it is shown how the thermal optimization of a LiDAR (light detection and ranging) sensor can be performed efficiently. This approach uses standard CAD (computer aided design) software, which is readily available, and saves time and cost as the thermal design can be optimized before experimental realisation. A four-step process was developed and realized: (i) Measurement of the thermal energy distribution of the current sensor design; (ii) Simulation of the time-dependant thermal behaviour using standard CAD software; (iii) Simulation of a thermally optimized design. This was compared quantitatively with the original design and was also used for verification of sufficient increase in heat dissipation; (iv) Experimental realisation and verification of the optimized design. It could be shown that the optimized prototype shows significantly improved thermal behaviour in accordance with the predictions from the simulations. The new LiDAR sensor shows lower heat generation and optimized dissipation of thermal energy which proofs the applicability of the approach to complex sensors.

An increasing number of underwater structures require regular, highly accurate inspections to maintain a safe and sustainable operation. Conventional sonar systems often lack the necessary resolution and precision, and camera-based systems are easily disturbed by turbid water. A technology which can bridge this gap is pulsed time-of-flight ranging. It provides higher resolution and precision compared to acoustic methods and tolerates turbid water. In this paper, we present a specialized underwater LiDAR (light detection and ranging) system which is capable of recording camera-like planar scenes using a two-dimensional beam-deflection unit. This is achieved using a combination of two rotating wedge-prisms mounted into custom-build motor modules which allows configurable linear, circular, and planar scan-patterns. Its compact design, paired with a large 33° deflection angle and 45 mm clear aperture makes it ideal for challenging underwater conditions.

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.

Over the past years a lot of effort is being focused on realizing the vision of fully autonomously driving vehicles. The achievement of this goal strongly depends on the development of sensors that allow the perception of the environment by scanning it with high speed, precision and resolution. The sensors employed in autonomous vehicles typically comprise cameras, Radar and LiDAR Systems. Especially LiDAR and Camera Sensors deliver the necessary high-resolution data, but both suffer from strongly degrading signals in low visibility conditions. To guarantee the safe operation of autonomously driving vehicles the existing sensors need to be improved with respect to these conditions and new sensors need to be developed. In this contribution we present a LiDAR system design that is optimized for the operation in low visibility conditions. On one hand we address the technical details of the system such as choice of laser, detector, deflection unit and signal processing electronics. Besides the technical details of the system, we discuss the physical and technological limitations such as wavelength dependent scattering and absorption and eye safety considerations. We further give an outlook on a sensor fusion approach with a time-gated sensor with high lateral resolution for a better recognition of objects obscured by scattering media.