Incidence angle influence on the quality of terrestrial laser scanning points

A terrestrial laser scanner measures the distance to an object with a precision in the order of millimeters. The quality of each single point in a point cloud affects post-processing applications, such as deformation analysis or 3D modeling. The quality of a scan point is influenced by four major factors: instrument calibration, atmospheric conditions, object properties and scan geometry. In this paper, the latter factor is investigated focusing on the influence of incidence angle, i.e. the angle between incoming laser beam and surface normal, on the precision of a scan point. It is shown that by considering the influence of incidence angle on the signal to noise ratio, the increase in measurement noise with increasing incidence angle can be successfully modeled. The implications of this model are demonstrated on two practical experiments. In the first experiment, a reference plate is scanned at a fixed distance but under different scan angles. The analysis shows that also in a practical setting the influence of incidence angle could be successfully isolated, allowing the conclusion that above 60º the incidence angle dominates the scan point precision. In the second experiment it is demonstrated that for a typical point cloud of a room, 20% of the measurement noise is due to incidence angle. The results of this research make it feasible to optimize the scan locations in a measurement setup in the sense that noise due to incidence angle is minimized.Earth Observation and Space SystemsAerospace Engineerin

EXAMINATION METHOD OF THE EFFECT OF THE INCIDENCE ANGLE OF LASER BEAM ON DISTANCE MEASUREMENT ACCURACY TO SURFACES WITH DIFFERENT COLOUR AND ROUGHNESS

Interest in the influence of the incidence angle of a laser beam to distance measurements can be seen in many areas of science and technology: geodesy, glaciology, archaeology, machine automation, and others. This paper presents results of measurements of the effect of the incidence angle of a laser beam to distance measurements to the surfaces of different colour and roughness by Topcon's electro-optical total station with an accuracy of 3 mm. Measurement method and the method of elimination of test stand errors are presented. The results of measurements have been analysed and the influence of selected factors (surface colour and roughness, lack of instrument rectification) on the distance measurement have been discussed. It is also shown the critical incidence angle above which it can be impossible to measure distances to reflective foil with tested total statio

Eolian sand transport monitored by terrestrial laser scanning

Morphodynamic changes at sandy coasts, as are dominant in The Netherlands, are typically monitored at yearly intervals by means of LIDAR. Meanwhile it is recognized that beach morphodynamics is not a regular process but is strongly correlated to meteorological conditions. A time series of 14 terrestrial laser scans of a beach experiment is analyzed, obtained during a time period of 88 hours characterized by changing weather conditions including strong wind and rain. It is shown that after a conversion to a suited spherical grid, different deformation regimes can be identified and that elevation changes rates below a millimeter an hour can be detected.Remote SensingAerospace Engineerin