Abstract
Terrestrial laser scanners (TLSs) can provide accurate and high-resolution data by measuring the distances (ranges) between the scanned points and the scanner center using time-of-flight or phase-shift-based methods. Distance measurement accuracy is of vital importance in TLSs and mainly influenced by instrument mechanism, atmospheric conditions, scanning geometry, and target surface properties. In general, existing commercial TLSs can achieve millimeter precision. However, significant errors (centimeter and even decimeter levels) beyond the instruments’ nominal accuracy exist in distance observations for targets with highly reflective surfaces whose specular reflections are dominant because these reflections can increase the backscattered laser signal power considerably and cause further disorder in the echo detection and recognition by TLS photodetectors. Apart from distance, the intensity value derived from the backscattered signal and influenced by the same factors as that of the distance measurement errors is recorded by TLSs. A certain link exists between the two instrumental observations. In this study, the anomalous distance measurement errors caused by target specular reflections are explored. The different planar reflective targets scanned by a Faro Focus3D 120 terrestrial scanner are used to experimentally investigate the relationship between the original intensity values and the distance measurement errors. Results imply that the distance measurement errors caused by specular reflections are not as erratic as they ostensibly seem. On the contrary, distance measurement errors are strongly related to the original intensity values. A polynomial can be established to empirically model the relationship between the original intensity data and the distance measurement errors. With use of the original intensity to compensate for the measured distance observations, the point cloud data accuracy can be improved by approximately 55.52%.
Highlights
Terrestrial laser scanning (TLS) is an outstanding technology for spatial and geographical data acquisition and has been widely used in various fields
This study aims to investigate the relationship between intensity and distance errors caused by target specular reflection characteristics
This study presents an intensity-based method for correcting the distance measurement errors caused by target specular reflections, thereby establishing a connection between the two types of data in TLS
Summary
Terrestrial laser scanning (TLS) is an outstanding technology for spatial and geographical data acquisition and has been widely used in various fields. The achievable distance precision is highly important in deciding whether TLS is suitable for a task or not [1]. Achievable distance precision determines the accuracy and reliability of the point cloud and the performance of the instrument. Distance measurement unit is a core component of TLSs. The investigation of distance measurement error sources and solutions is of vital importance to the improvement of TLS data accuracy and quality and has attracted widespread attention from manufacturers, users, and researchers in the past two decades [2,3,4,5,6,7,8,9]
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