Multi-Spectral Laser Scanning for Inspection of Building Surfaces - State of the Art and Future Concepts

Abstract

The Federal Institute for Materials Research and Testing (BAM) developed a multi-spectral laser scanner to demonstrate the advantages of such systems for the inspection of building surfaces. It is shown that damage of building surfaces, caused by enhanced moisture content and/or vegetation, can be recorded automatically with a high signal-to-noise ratio by using four continuous wave semiconductor lasers at different wavelengths for the defined illumination of the object surface. It is worked out that the damaged areas can be identified by applying commercial multi-spectral image processing software. Finally a concept is presented to improve the overall performance of the system with regard to sampling speed and sensitivity. Here the cw lasers are modulated by sinusoidal signals of different frequencies and the intensity of the backscattered laser light is detected by synchronous demodulation. Furthermore, these structured signals can be used for slant range measurements. Knowing the slant for each pixel, three dimensional multi-spectral images are obtained