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M. Zamecnikova, A. Wieser, H. Woschitz, C. Ressl:
"Influence of surface reflectivity on reflectorless electronic distance measurement and terrestrial laser scanning";
Journal of Applied Geodesy, 8 (2014), 4; 311 - 325.

The uncertainty of electronic distance measurement to surfaces rather than to dedicated
precision-reflectors (reflectorless EDM) is affected by the entire system comprising
instrument, atmosphere and surface. The impact of the latter is significant for applications like
geodetic monitoring, high-precision surface modelling or laser scanner self-calibration.
Nevertheless, it has not yet received sufficient attention and is not well understood.
We have carried out an experimental investigation of the impact of surface reflectivity on the
distance measurements of a terrestrial laser scanner. The investigation helps to clarify (i)
whether variations of reflectivity cause systematic deviations of reflectorless EDM, and (ii) if
so, whether it is possible and worth modelling these deviations. The results show that
differences in reflectivity may actually cause systematic deviations of a few mm with
diffusely reflecting surfaces and even more with directionally reflecting ones. Using a
bivariate quadratic polynomial we were able to approximate these deviations as a function of
measured distance and measured signal strength alone. Using this approximation to predict
corrections, the deviations of the measurements could be reduced by about 70% in our
experiment.
We conclude that there is a systematic effect of surface reflectivity (or equivalently received
signal strength) on the distance measurement and that it is possible to model and predict this
effect. Integration into laser scanner calibration models may be beneficial for high-precision
applications. The results may apply to a broad range of instruments, not only to the specific
laser scanner used herein.

Laser scanning; EDM; Signal strength; Calibration; Error modelling

http://dx.doi.org/10.1515/jag-2014-0016