Influence of surface reflectivity on reflectorless electronic distance measurement and terrestrial laser scanning

Zámečníková, Miriam; Woschitz, Helmut; Ressl, Camillo

doi:10.1515/jag-2014-0016

Cited by 36 publications

(32 citation statements)

References 6 publications

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“…With proper reference data, these profiles could be therefore used to identify the target material. The differences between materials for specific spectral bands agree with the error magnitudes identified in previous investigations on material-dependent uncertainties in reflectorless EDM (Zámečníková et al, 2014), signaling also that this approach holds potential to mitigate material-related uncertainties by accessing multispectral distance information unattainable for standard instruments. We have not yet investigated which are the dominant physical phenomena causing the observed distance dependencies with wavelength and material.…”

Section: Resultssupporting

confidence: 82%

An Instrumental Basis for Multispectral Lidar With Spectrally-Resolved Distance Measurements

Salido-Monzú

Wieser

2019

Int. Arch. Photogramm. Remote Sens. Spatial Inf. Sci.

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Commission II, WG II/3 KEY WORDS: Hyperspectral and multispectral LiDAR, reflectorless distance measurement, remote material probing, laser scanning, femtosecond laser ABSTRACT:Hyperspectral solutions augment laser scanning technology with material probing capabilities by measuring target reflectance along with topography. We propose a novel instrumental basis that enables also spectrally-resolved distance measurement with sufficient sensitivity as to access dispersive phenomena on the reflecting target and along the propagation medium, further enhancing the material analysis capabilities of hyperspectral approaches. To this end we have extended distance metrology using intermode beat notes of a mode-locked femtosecond laser to cover flexibly selected spectral regions. The approach is based on an ultra-broadband source derived from a femtosecond laser via coherent supercontinuum generation. Herein we provide a first demonstration of the successful application of this technique to reflectorless measurements and thus its feasibility for multispectral LiDAR. We use a table-top experimental set-up to assess the approach by measuring distance, spectrally-resolved relative distance and reflectance to 5 different material samples on 5 multiplexed contiguous spectral bands of 50 nm in the range of 600 nm to 850 nm. We have achieved a distance measurement precision and accuracy better than 100 µm using integration times of about 30 ms, with promising perspectives regarding scalability to practical distances. The spectrally-resolved distance measurements also show repeatable material-dependent profiles with differences between materials up to several tenths of mm in some spectral bands. Combined with simultaneously acquired reflectance estimations, these profiles enable collecting additional target information, indicating the potential of the approach to enhance the material probing capabilities of prospective multispectral laser scanners.

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Section: Resultssupporting

confidence: 82%

An Instrumental Basis for Multispectral Lidar With Spectrally-Resolved Distance Measurements

Salido-Monzú

Wieser

2019

Int. Arch. Photogramm. Remote Sens. Spatial Inf. Sci.

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“…Since the target center is estimated from this point cloud, it can be assumed that the geometry also has an influence on the precision of the TCE. Zámečníková et al [19] show that systematic errors in the single point measurement can also occur due to the incidence angle. 3.…”

Section: Influencing Factors On the Precision Of Target Center Estimamentioning

confidence: 99%

“…The algorithms are assumed to be unbiased, thus no systematics are expected. Only the systematic errors due to the incidence angle [19] remain. However, since the incidence angles during the scanning of targets are usually small and the error on the TCE will behave the same as for the single point measurement, this systematic error will not be examined further.…”

Section: Influencing Factors On the Precision Of Target Center Estimamentioning

confidence: 99%

Decreasing the Uncertainty of the Target Center Estimation at Terrestrial Laser Scanning by Choosing the Best Algorithm and by Improving the Target Design

et al. 2019

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During the registration and georeferencing of terrestrial laser scans, it is common to use targets to mark discrete points. To improve the accuracy of the registration, the uncertainties of the target center estimation (TCE) have to be minimized. The present study examines different factors influencing the precision of the TCE. Here, the focus is on the algorithm and the target design. It is determined that, in general, the uncertainties of the TCE are much smaller than those indicated by the manufacturers. By comparing different algorithms for the first time, it was possible to clearly determine that an algorithm using image correlations yields the smallest standard deviations for the TCE. A comparison of different target designs could not identify an ideal commercially available target. For this reason, a new target, the BOTA8 (BOnn TArget with 8-fold pattern) was developed, which leads to smaller standard deviations than the previous targets. By choosing the best algorithm and improving the target design, standard deviations of 0.5 mm in distance direction and 1.2 arcsec in angular direction for a scan distance up to 100 m were achieved with the laser scanner Leica ScanStation P20. The uncertainties could be reduced by several millimetres and angular seconds compared to the manufacturer’s targets and software.

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“…The further the points are away, the lower is the intensity by the inverse-square-law and therefore the likelihood for invalid points will increase. For the second argument the signal strength is not only relative to the material and the distance, but also to the angle of incidence (Zámečníková et al, 2014). When holes are developing, vertical edges become visible due to the displacement of covering material at the breakline.…”

Section: Preliminary Resultsmentioning

confidence: 99%

Monitoring and Deformation Analysis of Groynes Using TLS at the River Elbe

Tschirschwitz

Mechelke

Jansch

et al. 2016

Int. Arch. Photogramm. Remote Sens. Spatial Inf. Sci.

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To enter the Port of Hamburg, one of Europe’s busiest ports all vessels need to navigate around 145 km along the Elbe river, a tide influenced navigation channel. To protect the Elbe shoreline from erosion and to channel the waterway groynes (rigid hydraulic structures) have been built along the river. In the past years since ca. 2001 there has been a large increase in damage of groynes structural integrity at parts of the German waterways. The reason for this was determined in the ever growing size of container vessels passing by and inducing long periodical primary waves which have such a force that they erode the groynes rock structure. To analyse and improve the groynes structural resistance for vessel-induced long periodical wave loads an in-situ study is carried out at Juelssand, located at the Elbe river estuary. Over a period of two years the change of the geometrical structure of two different groyne shapes is monitored automatically by utilising two terrestrial laser scanners mounted in protective housings, located each on a 12 m high platform. The self-contained monitoring systems perform scanning of the two groynes one to two times a day at low tide, as the structures are fully submerged at high tide. The long-periodical wave loads are also determined using pressure sensors in each groyne. To correlate the captured data with vessel events and analyse the effects, vessel related parameters are recorded utilizing the Automatic Identification System (AIS). <br><br> This paper describes the automated processes for the data acquisition and focusses on the deformation that is calculated using current, extended and new algorithms of the Point Cloud Library. It shows the process chain from the acquisition of raw scan files from an elevated station to the filtering of point cloud, the registration, the calculation of pointwise changes and the aggregation to a grid for later correlation with ship parameters. When working outdoor in all kinds of weather conditions, the processes and equipment need to be robust and account for various cases and situations. This is especially applicable for the algorithms, which need to be adaptable to different scenarios like wet surfaces or snow and unwelcome objects ranging from flotsam to birds sitting on the groyne. At the current stage of the research, deformation in the magnitude of a couple of decimetres is observable. The orientation and location of the deformation is on the seaward side and corresponds to the lower distance of vessels leaving the harbour.

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Influence of surface reflectivity on reflectorless electronic distance measurement and terrestrial laser scanning

Cited by 36 publications

References 6 publications

An Instrumental Basis for Multispectral Lidar With Spectrally-Resolved Distance Measurements

An Instrumental Basis for Multispectral Lidar With Spectrally-Resolved Distance Measurements

Decreasing the Uncertainty of the Target Center Estimation at Terrestrial Laser Scanning by Choosing the Best Algorithm and by Improving the Target Design

Monitoring and Deformation Analysis of Groynes Using TLS at the River Elbe

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