Application Of Terrestrial Laser Scanning Research Articles

Testing the Application of Terrestrial Laser Scanning to Measure Forest Canopy Gap Fraction

Terrestrial laser scanners (TLS) have the potential to revolutionise measurement of the three-dimensional structure of vegetation canopies for applications in ecology, hydrology and climate change. This potential has been the subject of recent research that has attempted to measure forest biophysical variables from TLS data, and make comparisons with two-dimensional data from hemispherical photography. This research presents a systematic comparison between forest canopy gap fraction estimates derived from TLS measurements and hemispherical photography. The TLS datasets used in the research were obtained between April 2008 and March 2009 at Delamere Forest, Cheshire, UK. The analysis of canopy gap fraction estimates derived from TLS data highlighted the repeatability and consistency of the measurements in comparison with those from coincident hemispherical photographs. The comparison also showed that estimates computed considering only the number of hits and misses registered in the TLS datasets were consistently lower than those estimated from hemispherical photographs. To examine this difference, the potential information available in the intensity values recorded by TLS was investigated and a new method developed to estimate canopy gap fraction proposed. The new approach produced gap fractions closer to those estimated from hemispherical photography, but the research also highlighted the limitations of single return TLS data for this application.

Quantifying the effects of terrestrial laser scanner settings and survey configuration on land surface roughness measurement

The application of terrestrial laser scanning (TLS) for measuring Earth surface features is increasing. However, TLS surveys require users to choose and specify certain properties of the scan (i.e., resolution, height, distance, number of scan positions), often with limited understanding of how these properties affect the accuracy of the data. This paper presents results from an experiment that quantifies the effects of different scan settings and survey configurations on the measurement of centimeter-scale surface roughness. The main goal is to provide quantitative evidence to help guide and optimize field-based surface roughness measurements involving TLS data. The experiment involved an array of artificial roughness elements placed on an asphalt surface, similar to the approach of using inverted buckets in boundary layer experiments to simulate a rocky or sparsely vegetated surface with smooth interspaces. The independent variables consisted of laser point spacing, number of scan positions, and the height and distance of the scanner relative to the roughness array. The dependent variables were roughness element height, data occlusion, relative vertical accuracy, the root mean square height of the cup array, and the relative roughness of the asphalt surface. Two roughness patterns were tested, isotropic and anisotropic. Results show that when the laser point spacing was greater than the size of the individual roughness elements, their calculated height was between 32% and 73% below their actual height, but with a smaller spacing the calculated height was either equivalent to their actual height or only slight lower. Therefore, before a TLS survey is undertaken, manual measurements of roughness elements should be used to determine the size of the smallest roughness elements of interest, thus guiding the selection of laser point spacing. Larger point spacing also decreased the vertical accuracy of surfaces interpolated from the point clouds compared to global positioning system points. By combining point clouds from three scan stations arranged in a triangular network around the roughness array, the proportion of data occlusion decreased to as little as 0.24%, but due to error associated with point cloud registration, the accuracy of roughness element height decreased and the roughness of the asphalt surface artificially increased. For the most accurate measurements of the roughness element height and interspace roughness our results suggest that high-resolution point clouds obtained from one vantage point should be used. In regard to scanner height and distance, we measured a doubling of the occluded area when the scanner height decreased and distance to the array increased, thus increasing the angle of incidence. Reducing the angle of incidence decreases occlusion but also limits the areal coverage of each TLS scan and increases the number of scan stations at different vantage points required to cover large areas, which ultimately affects the accuracy of other roughness metrics. Overall, this case study demonstrates that there are trade-offs in that the optimization of one metric (e.g., roughness element height) can have negative effects on another (e.g., data occlusion). The choice of TLS settings and survey configuration, therefore, influences the accuracy of surface roughness measurements.

Use of terrestrial laser scanning (TLS) for monitoring and modelling of geomorphic processes and phenomena at a small and medium spatial scale in Polar environment (Scott River — Spitsbergen)

The application of Terrestrial Laser Scanning (TLS) for precise modelling of land relief and quantitative estimation of spatial and temporal transformations can contribute to better understanding of catchment-forming processes. Experimental field measurements utilising the 3D laser scanning technology were carried out within the Scott River catchment located in the NW part of the Wedel Jarlsberg Land (Spitsbergen). The measurements concerned the glacier-free part of the Scott River valley floor with a length of 3.5km and width from 0.3 to 1.5km and were conducted with a state-of-the-art medium-range stationary laser scanner, a Leica Scan Station C10. A complex set of measurements of the valley floor were carried out from 86 measurement sites interrelated by the application of 82 common ‘target points’. During scanning, from 5 to 19 million measurements were performed at each of the sites, and a point-cloud constituting a ‘model space’ was obtained. By merging individual ‘model spaces’, a Digital Surface Model (DSM) of the Scott River valley was obtained, with a co-registration error not exceeding ±9mm. The accuracy of the model permitted precise measurements of dimensions of landforms of varied scales on the main valley floor and slopes and in selected sub-catchments. The analyses verified the efficiency of the measurement system in Polar meteorological conditions of Spitsbergen in mid-summer.

Selected Aspects of the Application of Terrestrial Laser Scanning as a Tool to Support the Development of Rural Areas.

Selected Aspects of the Application of Terrestrial Laser Scanning as a Tool to Support the Development of Rural Areas.

Detecting Changes in Forest Structure over Time with Bi-Temporal Terrestrial Laser Scanning Data

Changes to stems caused by natural forces and timber harvesting constitute an essential input for many forestry-related applications and ecological studies, especially forestry inventories based on the use of permanent sample plots. Conventional field measurement is widely acknowledged as being time-consuming and labor-intensive. More automated and efficient alternatives or supportive methods are needed. Terrestrial laser scanning (TLS) has been demonstrated to be a promising method in forestry field inventories. Nevertheless, the applicability of TLS in recording changes in the structure of forest plots has not been studied in detail. This paper presents a fully automated method for detecting changes in forest structure over time using bi-temporal TLS data. The developed method was tested on five densely populated forest plots including 137 trees and 50 harvested trees in point clouds. The present study demonstrated that 90 percent of tree stem changes could be automatically located from single-scan TLS data. These changes accounted for 92 percent of the changed basal area. The results indicate that the processing of TLS data collected at different times to detect tree stem changes can be fully automated.

Validation of terrestrial laser scanning and photogrammetry techniques for the measurement of vertical underclearance and beam geometry in structural inspection of bridges

This research shows a novel methodology based on the application of terrestrial laser scanning and photogrammetry techniques as auxiliary metric tools for bridge inspections procedures. These methodologies are validated throughout a case study where the minimum underclearance and the overall geometry of a prestressed concrete beam are obtained. Data obtained are compared with high accurate measurements provided by a total station. Results show a good agreement for beam geometry with high statistical correlation coefficients. Minimum vertical underclearance also shows a good agreement for all the systems, which appears good enough due the metric tolerances required in these inspection works.

Improving particulate carbon loss estimates in eroding peatlands through the use of terrestrial laser scanning

Blanket bogs act as the largest terrestrial store of carbon within the UK. Unfortunately many are degraded with exacerbated erosion being common. Although considerable efforts have been made to quantify carbon fluxes across blanket bogs, less attention has focussed on quantifying losses associated with erosion. Traditional approaches to measuring erosion have relied on erosion pins and sediment traps. However, both methods suffer from several problems and are unable to provide data over large areas. Terrestrial laser scanning has been used widely in geomorphology to create detailed 3D topographic maps in a range of environments. A pilot study was carried out over winter 2010–2011 to test the applicability of terrestrial laser scanning to measure erosion across a blanket bog within the North Pennines, UK. The technique was found to be superior to traditional methods providing high resolution spatial data on surface elevation change. A net increase in the peat surface height of 2.5mm was calculated from the terrestrial laser scans between October 2010 and March 2011. This compares with a net surface lowering of 38mm measured using pins. These results suggest that previous erosion data from peatland sites based on pin measurements ought to be treated with caution. However, several improvements are required to the laser scanning technique before it is fully implemented in peatland environments including the development of a filter to remove vegetation from the scan results, and taking account of ‘mire-breathing’ which can cause surface level rise and fall in peatlands. It is clear that once these factors are dealt with, regular repeated ground based laser scanning will vastly improve our understanding of the role of processes that affect the surface elevation of peatlands including the relative roles of storm events and long-term seasonal cycles, and ‘roughening’ of the peat surface as a result of needle-ice formation, desiccation and wind-scouring.

TERRESTRIAL LASER SCANNING FOR COASTAL GEOMORPHOLOGIC RESEARCH IN WESTERN GREECE

Abstract. We used terrestrial laser scanning (TLS) for (i) accurate volume estimations of dislocated boulders moved by high-energy impacts and for (ii) monitoring of annual coastal changes. In this contribution, we present three selected sites in Western Greece that were surveyed during a time span of four years (2008-2011). The Riegl LMS-Z420i laser scanner was used in combination with a precise DGPS system (Topcon HiPer Pro). Each scan position and a further target were recorded for georeferencing and merging of the point clouds. For the annual detection of changes, reference points for the base station of the DGPS system were marked. Our studies show that TLS is capable to accurately estimate volumes of boulders, which were dislocated and deposited inland from the littoral zone. The mass of each boulder was calculated from this 3D-reconstructed volume and according density data. The masses turned out to be considerably smaller than common estimated masses based on tape-measurements and according density approximations. The accurate mass data was incorporated into wave transport equations, which estimate wave velocities of high-energy impacts. As expected, these show smaller wave velocities, due to the incorporated smaller mass. Furthermore, TLS is capable to monitor annual changes on coastal areas. The changes are detected by comparing high resolution digital elevation models from every year. On a beach site, larger areas of sea-weed and sandy sediments are eroded. In contrast, bigger gravel with 30-50 cm diameter was accumulated. At the other area with bigger boulders and a different coastal configuration only slightly differences were detectable. In low-lying coastal areas and along recent beaches, post-processing of point clouds turned out to be more difficult, due to noise effects by water and shadowing effects. However, our studies show that the application of TLS in different littoral settings is an appropriate and promising tool. The combination of both instruments worked well and the annual positioning procedure with own survey point is precose for this purpose.

Automatic Stem Mapping Using Single-Scan Terrestrial Laser Scanning

The demand for detailed ground reference data in quantitative forest inventories is growing rapidly, e.g., to improve the calibration of the developed models of airborne-laser-scanning-based inventories. The application of terrestrial laser scanning (TLS) in the forest has shown great potential for improving the accuracy and efficiency of field data collection. This paper presents a fully automatic stem-mapping algorithm using single-scan TLS data for collecting individual tree information from forest plots. In this method, the stem points are identified by the spatial distribution properties of the laser points, the stem model is built up of a series of cylinders, and the location of the stem is estimated by the model. The experiment was performed on nine plots with 10-m radius. The stem-location maps measured in the field by traditional methods were used as the ground truth. The overall stem-mapping accuracy was 73%. The result shows that, in a relatively dense managed forest, the majority of stems can be located by the automatic algorithm. The proposed method is a general solution for stem locating where particular plot knowledge and data format are not required.

Improving Completeness of Geometric Models from Terrestrial Laser Scanning Data

The application of terrestrial laser scanning for the documentation of cultural heritage assets is becoming increasingly common. While the point cloud by itself is sufficient for satisfying many documentation needs, it is often desirable to use this data for applications other than documentation. For these purposes a triangulated model is usually required. The generation of topologically correct triangulated models from terrestrial laser scans, however, still requires much interactive editing. This is especially true when reconstructing models from medium range panoramic scanners and many scan positions. Because of residual errors in the instrument calibration and the limited spatial resolution due to the laser footprint, the point clouds from different scan positions never match perfectly. Under these circumstances many of the software packages commonly used for generating triangulated models produce models which have topological errors such as surface intersecting triangles, holes or triangles which violate the manifold property. We present an algorithm which significantly reduces the number of topological errors in the models from such data. The algorithm is a modification of the Poisson surface reconstruction algorithm. Poisson surfaces are resilient to noise in the data and the algorithm always produces a closed manifold surface. Our modified algorithm partitions the data into tiles and can thus be easily parallelized. Furthermore, it avoids introducing topological errors in occluded areas, albeit at the cost of producing models which are no longer guaranteed to be closed. The algorithm is applied to scan data of sculptures of the UNESCO World Heritage Site Schönbrunn Palace and data of a petrified oyster reef in Stetten, Austria. The results of the method’s application are discussed and compared with those of alternative methods.

Adjustment of systematic errors in ALS data through surface matching

Surface matching is a well researched topic in both Computer Vision (CV) and terrestrial laser scanning (TLS) or ground based light detection and ranging (LiDAR), but the extent of the range images derived from these technologies is typically orders of magnitude smaller than those derived from airborne laser scanning (ALS), also known as airborne LiDAR. Iterative closest point (ICP) and its variants have been successfully used to align and register multiple overlapping views of the range images for CV and TLS applications. However, many challenges are encountered in applying the ICP approach to ALS data sets. In this paper, we address these issues, explore the possibility of automating the algorithm, and present a technique to adjust systematic discrepancies in overlapping strips, using geometrical attributes in a given terrain. In this method, the ALS point samples used in the algorithm are selected depending on their ability to constrain the relative movement between the overlapping laser strips. The points from overlapping strips are matched through modified point to plane based on the ICP method.

The application of terrestrial laser scanning to aeolian saltation cloud measurement and its response to changing surface moisture

AbstractSaltation is the dominant form of aeolian transport of sand sized grains, yet its heterogeneous spatial and temporal distribution, and inherent feedback and interaction with the surface over which sand is transported, hinders large scale quantification. In this letter we present preliminary data on saltation cloud characteristics quantified using terrestrial laser scanning (TLS). These data, together with surface moisture and surface roughness patterns, elucidate the importance of saltation in the development of protodunes on a drying beach, and indicate the potential usefulness of TLS in examining aeolian processes in both beach and desert environments. Copyright © 2010 John Wiley & Sons, Ltd.

Reply to the discussion by Olsen and Stuedlein on “Use of terrestrial laser scanning for the characterization of retrogressive landslides in sensitive clay and rotational landslides in river banks”Appears in Canadian Geotechnical Journal, 47(10): 1164–1168.

In their discussion about aerial laser scanning (ALS) and terrestrial laser scanning (TLS), Olsen and Stuedlein present some issues than we did not address in our paper (Jaboyedoff et al. 2009a). Our study deals with compact landslide bodies and we had to overcome many related problems, such as shadowing, vegetation, site accessibility, and safety issues. In contrast, Olsen and Stuedlein deal with linear, clean features (coastal cliffs), which enable a completely different way of working. Nonetheless, their remarks are relevant and they were not addressed in our paper because it was beyond the scope of our study. Studies on landslide volumes and mechanisms do not in general need a high accuracy, while it is crucial for landslide movement monitoring. In their discussion, Olsen and Stuedlein give some examples of TLS applications in landslide studies in addition to those highlighted in our article. Most of them relate to coastal erosion and rockfalls in cliffs, and only a few relate to landslides. For the sake of completeness of the literature overview, TLS has also been widely used for

Terrestrial Laser Scanning of grain roughness in a gravel-bed river

This paper demonstrates the application of Terrestrial Laser Scanning (TLS) to determine the full population of grain roughness in gravel-bed rivers. The technique has the potential to completely replace the need for complex, time-consuming manual sampling methods. Using TLS, a total of 3.8 million data points (mean spacing 0.01 m) were retrieved from a gravel bar surface at Lambley on the River South Tyne, UK. Grain roughness was extracted through determination of twice the local standard deviation (2 σ z ) of all the elevations in a 0.15 m radius moving window over the data cloud. 2 σ z values were then designated to each node on a 5 cm regular grid, allowing fine resolution DEMs to be produced, where the elevation is equivalent to the grain roughness height. Comparisons are made between TLS-derived grain roughness and grid-by-number sampling for eight 2 m 2 patches on the bar surface. Strong relationships exist between percentiles from the population of 2 σ z heights with measured a-, b-, and c-axes, with the closest matches appearing for the c-axis. Although strong relationships exist between TLS-derived grain roughness (2 σ z ), variations in the degree of burial, packing and imbrication, results in very different slope and intercept exponents. This highlights that conventional roughness measurement using gravel axis length should be used with caution as measured axes do not necessarily represent the actual extent to which the grain protrudes into the flow. The sampling error inherent in conventional sampling is also highlighted through undertaking Monte Carlo simulation on a population of 2000 clasts measured using the grid-by-number method and comparing this with the TLS-derived population of grain roughness heights. Underestimates of up to − 23% and overestimates of up to + 50% were found to occur when considering the D 84, and − 20% and overestimates of up to + 36% were found to occur when considering the D 50.

Three-dimensional (3D) visualisation: the application of terrestrial laser scanning in the investigation of historical Scottish farming townships

Recent developments in digital technologies are heralding significant changes in the way we acquire, visualise and analyse archaeological data. Terrestrial laser scanners can be used to create photo-realistic virtual copies of landscapes, and archaeological features, and offer the potential to improve our understanding of three-dimensional (3D) spatial relationships at study sites. Here we present a methodology for the integration of a high-resolution 3D site model with soil chemical data obtained from an abandoned settlement site located in the Central Highlands of Scotland. At this site, the multi-element concentration in soil, co-visualised within a topographic setting, has an important role to play in elucidating settlement layout and activity. The methods described here are also of significance in archiving sites of archaeological/historical importance where development activities and/or environmental processes may destroy remains, or where access to field sites is restricted.

Assessing the applicability of terrestrial laser scanning for spatial snow depth measurements

Abstract Snow depth observation in potentially dangerous avalanche-starting zones is important for avalanche prediction and dimensioning of permanent protection measures. The possible danger of avalanches complicates measurements of snow depth in the field (e.g. by probing). Therefore, the applicability of terrestrial laser scanning to measure the depth of the snow cover was analysed. Different long-range laser profile measuring systems were used carrying out numerous field campaigns (Vorarlberg, Austrian Alps). The objective of the study was to discover under which meteorological and snowpack conditions the measurements must be taken in order to provide accurate results ( 1 mm) only 50% of the emitted signal was received, depending on the angle of incidence. In any case, the accuracy decreases with increasing distance to the target. For distances to the object of more than about 500 m, the accuracy that can be achieved with the used TLS measuring systems is rather low and the errors can be significantly larger than 10 cm.

Application of Terrestrial Laser Scanning in determining the pattern of late Pleistocene and Holocene fault displacement from the offset of pluvial lake shorelines in the Alvord extensional basin, northern Great Basin, USA

The northwardtrending Alvord extensional basin of southeastern Oregon lies along the northern margin of the Great Basin. The basin is nearly 200 km long and 15 km wide and is bound and internally dissected by a complex system of active normal faults. The faults cut Pleistocene wave-cut terraces that formed along successive shorelines of pluvial Lake Alvord. The wave-cut terraces are incised into late Tertiary volcanic and sedimentary rocks and unconsolidated Quaternary sediments. The terraces formed during stillstands of the ancient lake, during at least two cycles of lake fill and desiccation in the Pleistocene. Wave-cut terraces are divided into two sets, with the topographically higher and older Serrano terrace series consisting of three shorelines and the Alvord terrace series composed of the five topographically lower and younger shorelines. Shorelines are dated locally, and together with regional correlation to other pluvial lakes, the Serrano highstand is estimated as 200–130 ka and the Alvord highstand as 20–15 ka. High-resolution topographic images of the terrace morphology acquired by Terrestrial Laser Scanning georeferenced with the Global Positioning System allowed detailed analysis of shoreline altitudes where they are crosscut by faults. Variation in shoreline altitude measured across faults and on opposing sides of the basin indicates that fault slip occurred during and following periods of lake-level recession. The Serrano terrace highstand records a cumulative vertical displacement of 137.5 ± 3.6 m and the vertical offset of the younger Alvord terrace series highstand is 72.5 ± 2.8 m. Fault displacement is heterogeneously distributed across the basin. Faults along the western margin of the basin accommodated nearly 50% of the total displacement, with one fault accommodating over 20% of the total displacement budget. The residual displacement is distributed across the basin. As much as 30% of the cumulative offset is taken up by structures concealed beneath basin cover and 20% by structures exposed in the highlands along the eastern flank of the basin. Since formation of the Alvord shorelines, the rate of fault displacement was nonperiodic and the basin underwent elevated activity in the late Pleistocene and early Holocene. Vertical displacement rates vary through time, and offset of Alvord terraces occurred at 3.6–7.3 mm/yr, whereas displacement of the Serrano terraces ranged from 0.7 to 1.1 mm/yr. When the horizontal component of motion is calculated by using fault dips of 60°, the 104 yr time-scale rate determined from the Alvord terraces is as much as 2.4–4.2 mm/yr and exceeds the contemporary horizontal displacement across the basin of 1.75 mm/yr determined geodetically. The 105 yr horizontal displacement rate calculated for the Serrano highstand is substantially lower, 0.4–0.6 mm/yr. Spatial and temporal pattern of faulting within the Alvord basin illustrates the complexity of strain release within the basin and highlights the length- and time-scale dependence of deformation rate estimation within extensional basins.

On-the-job detection and correction of systematic cyclic distance measurement errors of terrestrial laser scanners

Application of terrestrial laser scanning for engineering and documentation projects requiring high accuracy is often prohibitive due to the error budget of terrestrial laser scanners (TLS) which is worse than that of alternative instruments such as total stations. However, by separating the errors of TLS into random and systematic components, the influence of both can be reduced significantly. Approaches for reducing the influence of random noise rely on averaging. One method is introduced briefly as it is relevant for the task of the proposed systematic error removal. We discuss the correction of cyclic distance measurement errors of TLS in detail. For the investigated scanner, these cyclic errors are the most dominant systematic errors. The proposed approach is based on an on-the-job determination of a distance correction function which allows reducing the magnitude of the occurring distance errors by a factor of ten, reducing the systematic errors to less than 0.5 mm. The massive amount of data acquired by TLS is exploited using robust statistical methods. The algorithm developed relies on small, flat surfaces found automatically in the scene. Hence, the method can be applied on engineering project data without requiring additional laboratory experiments. Therefore, it is not essential that the errors are constant over time. By the introduction of on-the-job correction procedures as the one proposed, the systematic errors of TLS can be decreased significantly. This makes them more suitable to be used as an alternative to single point measurement devices.