Abstract:The uncertainty of electronic distance measurement to surfaces rather than to dedicated precisionre ectors (re ectorless EDM) is a ected by the entire system comprising instrument, atmosphere and surface. The impact of the latter is signi cant for applications like geodetic monitoring, high-precision surface modelling or laser scanner self-calibration. Nevertheless, it has not yet received su cient attention and is not well understood. We have carried out an experimental investigation of the impact of surface re ectivity on the distance measurements of a terrestrial laser scanner. The investigation helps to clarify (i) whether variations of re ectivity cause systematic deviations of re ectorless EDM, and (ii) if so, whether it is possible and worth modelling these deviations. The results show that di erences in re ectivity may actually cause systematic deviations of a few mm with di usely reecting surfaces and even more with directionally re ecting 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 re ectivity (or equivalently received signal strength) on the distance measurement and that it is possible to model and predict this e ect. Integration into laser scanner calibration models may be bene cial for highprecision applications. The results may apply to a broad range of instruments, not only to the speci c laser scanner used herein.

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