Intensity measurements

Laser scanners determine the geometry of objects and surfaces using distance measurements. State-of-the-art systems also record the intensity of the light scattered back when doing so. Evaluating the intensity of the light scattered back allows a photo-realistic image of the surrounding area to be generated. Parallel system approaches can be implemented in order to be independent of light source and geometry-measurement receiver electronics. Defined light wavelengths, an ideally shaped measurement beam and parallelized detectors are required for generating an ideal image of the measuring object. This achieves resolutions in the region of one millimeter even for mobile laser-scan systems and with high travel speed. 

Topographical and intensity measurement of a road surface
© Fraunhofer IPM
Topography and intensity measurement of a road surface at a driving speed of 80 km/h. The lines show the cross-sections along the direction of movement. The red 3D scan lines run at a distance of 28 mm perpendicular to the direction of travel. The green lines of the 2D intensity scan have a distance of 1.7 mm. The picture below right shows the individual measuring points and their distance to each other perpendicular to the movement.

In addition to the 3D geometry of objects, their surface is often also of interest. The requirements here reach down to the submillimeter range. Mobile platforms moving at typical speeds of 80 km/h have so far only been able to capture intensity images by using special camera systems and strong, active lighting. However, their focus range and field of vision are very limited. Subsequently, the camera images obtained must be consistently combined in an elaborate process.

Fraunhofer IPM has developed and patented an innovative technology that simultaneously captures 3D images and high-resolution 2D surface images - without using a camera. For this concept, an intensity scanner for the 2D information and a distance scanner for the 3D information were combined in an optical setup. Based on this concept, compact devices are feasible where the units are calibrated to one another. In the previous version, the 2D image has a resolution 16 times higher than the 3D image.

The photorealistic display has three central advantages: it is completely independent of ambient lighting and has a high depth of field. In addition, the pure hardware calibration eliminates the need for time-consuming post-processing such as stitching.

The technology makes it possible, for example, to detect damages to asphalt or concrete in the sub-millimetre range, from carrier platforms moving at speeds of over 80 km/h.



Systems for pavement profile measurement

In addition to the scan profile, the Pavement Profile Scanner PPS-Plus captures a high-resolution intensity image of the road surface on which even smaller defects, such as cracks, can be detected.