Calibration of a Terrestrial Laser Scanner - Institute of Geodesy and ...

1Introduction1.1 Terrestrial Laser ScanningFor several years now, terrestrial laser scanning (TLS) has become an additional data acquisition techniquein geodesy. The development of laser scanners is in its infancy. Therefore, the scanners do not have thesame properties, e.g. accuracy, precision, reproducibility, repeatability, and reliability, as traditional geo¬detic instruments, e.g. automated total station and global positioning systems (GPS). However, furthertechnological developmentswill lead to advanced instruments in the near future. Theinterests of geodesistsregarding centering, levelling, real time processing of data (and not only in-situ controlling of acquireddata), etc. require close cooperation with manufacturers. Nowadays, the second to third generation ofsuch instruments is available on the market. Geodesists are not the only ones interested in laser scanning.The use of terrestrial laser scanners is widespread in production lines, plants, cultural heritage, industrialmetrology etc. The application area is growing nearly everyday. In geology, crime scene investigation andengineering geodesy, terrestrial laser scanning is relatively new.Terrestrial laser scanning technology has been strongly influenced by the developmentof LiDAR, an ac¬ronym for light detecting and ranging, which started in the 1970's. LiDAR has been successfullymore than 30 years in airborne and remote sensing applications. The delay in adoptingused forLiDAR in terrestrialinstruments involves providing for short ranges, i.e.less than one kilometer, and increased accuracy, i.e.less than one decimeter.These have been made possible by technological developments since the 1990's,such as:• improvements in microchip laser technology• manufacturing of optical elements• development of micro-electro-mechanical systems• improvements in computer technology• data processing algorithmsConsequently, the performance of data capturing, the accuracy in range measurement, the reliability ofacquired data etc. have increased and the instrumental design, i.e. weight and dimensions, the costs etc.have decreased.A LiDAR unit consists roughly of an emitter, a receiver and a detector system. The carrier is a laser, whichcontains the modulated information required for detecting the travel time from emitter to objectsLasers differ in power and wavelength, with power limited to a maximum value for eye safety.for solving the range is based on continuous waveforms or direct time-of-flight. Scattered lightand back.The methodis receivedat fixed time intervals. For detecting the laser beam, highly sensitive diodes have to be implemented. The