engleski

Comparison of Terrestrial Laser Scanners for slope stability monitoring

Terrestrial laser scanning (TLS) is a technology that allows non-contact determination of large amounts of points in a relatively short time. Although the basic principle of measurement is known, there is no universal terrestrial laser scanner that could perform all types of measurements. Therefore, there are classifications of terrestrial laser scanners according to principles that are used for distance measurement (pulse, phase shift), as well as classifications of TLS according to laser beam deflection method to camera, panoramic and hybrid scanners. Because of various classifications of TLS's, it is not possible to directly compare technical specifications of instruments which make it difficult for customers to choose the right scanner for specific projects. Since there is no standard, it is necessary to investigate terrestrial laser scanners to obtain independent accuracy/precision estimates and develop standardized calibration models and procedures. Thus, in this article two terrestrial laser scanners from different manufactures were tested: Faro Focus 3D and Optech ILRIS. Instruments used in this research vary according to range measurement as well as deflection of the laser beam principle. In the experiments identifying distance measurement errors which occur due to erroneous laser beam reflection from some specific material or specific color was concentrated on. Measurements with terrestrial laser scanners as well as other surveying methods contain errors that are caused by a variety of sources and influences relevant to all processes of determining spatial data. TLS's consists of a series of optical, electronic and mechanical parts, which are all a potential source of errors. If a TLS is used in highly specialized conditions such as landslide surface movements or surface deformation analysis, comprehensive knowledge of all error sources is required for correctly interpreting collected data. Errors in TLS measurements can be divided into four classes: instrumental, object related, environmental and methodological errors. Therefore, the performed research in which investigation on standard parameters of laser scanners (accuracy, resolution, time) and some features of the "real" conditions of measurements that depend on the selection of laser scanner (precision measurements at different distances, the time required to collect detailed points, the intensity of the return signals from different materials of the subject) were preformed. Laboratory tests were performed on the Faculty of Geodesy in Zagreb, however in addition to laboratory tests geodetic measurements on the field during a period of one year were also performed. For the field tests a location of unstable block in the area of old town Omiš suitable for recording was determined and measured. Collected data and preformed analysis will be further presented in this article. Terrestrial laser scanner Faro Focus 3D is based on phase shift distance measurement method with a range of 120 m from targets having a minimum of 90% reflectivity. Field of view of the afore scanner is 360x305 degrees. Accuracy of distance measurement is 2 mm at 25 m and it has an integrated camera with a resolution of 70 MPx for the entire field of view. Scanner is controlled by touch screen directly on the device or remotely (notebook, PDA, Smartphone) using Wi-Fi and the collected data is stored on an SD card. Faro Focus 3D, also has a dual-axis compensator allowing for setting up of the scanner like a total station. Optech Ilris 360 is a pulse based distance measurement method scanner. It has an accuracy of about 7 mm at 200 m. This type of laser scanner can determine distances up to 1500 m depending on reflectivity of object. Its field of view is 40x40 degrees but it can be extended by using a pan/tilt base to 360x220 degrees. The scanner is controlled by notebook via Ethernet cable or by a remote device using Wi- Fi network. Field data can be stored in an internal or external memory.

TLS ; Faro ; ILRIS-3D ; comparison

nije evidentirano