Fraunhofer Institute for Physical Measurement Techniques IPM
The Underwater LiDAR System (ULi) is based on the principle of pulsed time-of-flight (ToF) measurement and designed for high-resolution 3D inspection tasks. It captures fine geometric details over distances of several tens of meters, allowing for accurate documentation and assessment of underwater objects. With millimeter-level precision, the ULi provides a significantly higher spatial resolution than conventional sonar-based systems. This makes it well suited for detailed inspections, condition monitoring, and dimensional analysis.
In addition to the measurement hardware, the system includes algorithms for efficient data processing and evaluation.
Efficient static and dynamic scanning of large areas
The ULi sensor can be operated statically or on underwater inspection vehicles such as ROVs or ships. Two rotating wedge prisms project a laser beam on the surroundings and detect the returning light. Pulsed ToF technology is used to measure the distance from the scanner to the object. The exact position of each measurement point is calculated from the measured distance value and the angle of the scanning prisms. The backscattered signal is recorded at the detector in its full waveform in order to perform sophisticated analyses in post-processing.
The system works at scanning frequencies in the range of 2 × 25 Hz with a sampling frequency of up to 100,000 points per second and a scanning angle of up to 44° in water. The rotating prisms allow the entire field of view (FoV) to be captured without moving the sensor. The shape of the FoV can be linear, circular, or planar. It can be dynamically adapted to the individual application. Range and precision strongly depend on the water quality. In clear water, a scanning range of several tens of meters and submillimeter precision are achievable. In turbid water, a measurement range of two times the Secchi depth is feasible.
Customization and implementation
Upon request, the ULi sensor can be customized according to application by adapting the scanner’s opening angle, the measurement, or the scanning rate. Housing size and diving depth are also customizable. We adapt the system for either stationary or mobile use on ROVs or ships in close cooperation with the end user. Adjustable interfaces allow for application-specific design and integration.