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A multispectral tunnel inspection system for simultaneous moisture and shape detection
Author(s): Valentin Vierhub-Lorenz; Katharina Predehl; Sebastian Wolf; Christoph S. Werner; Frank Kühnemann; Alexander Reiterer
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Paper Abstract

In this paper, we present the implementation of a differential-absorption measurement-technique for surface moisture detection into a laser scanner aiding modern tunnel inspections. The use of laser scanners for tunnel inspections can reduce costly tunnel closures and provide digital data, compliant with modern building information modeling (BIM). Unfortunately, available systems are typically limited to pure 3D mapping. The Fraunhofer Institute for Physical Measurement Techniques IPM is developing a novel multi-parameter laser scanning system. For the first time, this system allows the simultaneous measurement of 3D-geometry, remission and surface moisture. The scanner measures simultaneously with two collinear laser beams with distinct wavelengths. One is centered at the absorption band of water at 1450 nm wavelength, while the other, with 1320 nm wavelength, is used as an intensity reference. The intensity ratio gives a good estimate of the surface water content. Additionally, the power of both lasers is modulated with a high frequency. This enables simultaneous measurement of the distance by comparing the phase difference of the backscattered light with a local reference. With this approach, we are able to record up to two million points per second containing distance, intensity and moisture information. Besides the technical implementation, we present point clouds from multiple test objects and surfaces. The presented data nicely demonstrates the ability to differentiate between absolute intensity variations, e.g. caused by dirt, and actual water contamination.

Paper Details

Date Published: 2 October 2019
PDF: 7 pages
Proc. SPIE 11157, Remote Sensing Technologies and Applications in Urban Environments IV, 111570T (2 October 2019); doi: 10.1117/12.2533101
Show Author Affiliations
Valentin Vierhub-Lorenz, Fraunhofer Institute for Physical Measurement Techinques IPM (Germany)
Katharina Predehl, Fraunhofer Institute for Physical Measurement Techniques IPM (Germany)
Sebastian Wolf, Fraunhofer Institute for Physical Measurement Techniques IPM (Germany)
Christoph S. Werner, Fraunhofer Institute for Physical Measurement Techniques IPM (Germany)
Frank Kühnemann, Fraunhofer Institute for Physical Measurement Techniques IPM (Germany)
Alexander Reiterer, Fraunhofer Institute for Physical Measurement Techniques IPM (Germany)
Albert-Ludwigs-Univ. Freiburg (Germany)


Published in SPIE Proceedings Vol. 11157:
Remote Sensing Technologies and Applications in Urban Environments IV
Thilo Erbertseder; Nektarios Chrysoulakis; Ying Zhang; Frank Baier, Editor(s)

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