Terrestrial laser scanning (TLS) is a surveying technology to measure distances<br>to surfaces in the spherical surrounding of the scanner instrument. In contrast to<br>pulse, i.e. time of flight scanners, phase based scanners emit a modulated wave signal<br>that allows for determining the object distance from the returned phase pattern.<br>Because of their high scanning speed, phase based instruments are getting more and<br>more popular. It is clear from literature and practice that, because of the interaction<br>between the laser light and the object, the characteristics of the object surface have a<br>large influence on the measurement quality. Still, a quantitative insight in the quality<br>of scanning results is missing.<br>This publication will compare two phase based scanners, the Imager5003<br>from Zoller und Fröhlich and the HS880 from Faro. We investigate the scan<br>quality of both scanners for a variety of surfaces with different reflection<br>characteristics. For this purpose scans of an Esser Test Chart TE 109 were made<br>with both scanners. The test chart consists of six different grey patches ranging<br>from 71% remission white to 0.05% remission black. The chart was scanned<br>from a distance of 4 m in a stable environment. In order to compare the scanning<br>results of both scanners a patch wise analysis is made of (i) the number of points<br>scanned, (ii) the intensities values of the scanned points, and (iii) the reliability<br>and precision of a local plane adjustment.<br>It turns out that for both scanners the measurement noise is significantly<br>increasing with decreasing remission. An insight in the amount of absorbed and<br>reflected energy per grey value patch will be part of the analysis results. An overall<br>conclusion of the presented experiment is that the two scanners differ only in extreme<br>cases from the specifications given by the manufacturers.


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