Potential Of Terrestrial Laser Scanning Research Articles

Terrestrial Laser Scanning: An Operational Tool for Fuel Hazard Mapping?

Fuel hazard estimates are vital for the prediction of fire behaviour and planning fuel treatment activities. Previous literature has highlighted the potential of Terrestrial Laser Scanning (TLS) to be used to assess fuel properties. However, operational uptake of these systems has been limited due to a lack of a sampling approach that balances efficiency and data efficacy. This study aims to assess whether an operational approach utilising Terrestrial Laser Scanning (TLS) to capture fuel information over an area commensurate with current fuel hazard assessment protocols implemented in South-Eastern Australia is feasible. TLS data were captured over various plots in South-Eastern Australia, utilising both low- and high-cost TLS sensors. Results indicate that both scanners provided similar overall representation of the ground, vertical distribution of vegetation and fuel hazard estimates. The analysis of fuel information contained within individual scans clipped to 4 m showed similar results to that of the fully co-registered plot (cover estimates of near-surface vegetation were within 10%, elevated vegetation within 15%, and height estimates of near-surface and elevated strata within 0.05 cm). This study recommends that, to capture a plot in an operational environment (balancing efficiency and data completeness), a sufficient number of non-overlapping individual scans can provide reliable estimates of fuel information at the near-surface and elevated strata, without the need for co-registration in the case study environments. The use of TLS within the rigid structure provided by current fuel observation protocols provides incremental benefit to the measurement of fuel hazard. Future research should leverage the full capability of TLS data and combine it with moisture estimates to gain a full realisation of the fuel hazard.

Shifts in structural diversity of Amazonian forest edges detected using terrestrial laser scanning

Forest edges are an increasingly common feature of Amazonian landscapes due to human-induced forest fragmentation. Substantial evidence shows that edge effects cause profound changes in forest biodiversity and productivity. However, the broader impacts of edge effects on ecosystem functioning remain unclear. Assessing the three-dimensional arrangement of forest elements has the potential to unveil structural traits that are scalable and closely linked to important functional characteristics of the forest. Using over 600 high-resolution terrestrial laser scanning measurements, we present a detailed assessment of forest structural metrics linked to ecosystem processes such as energy harvesting and light use efficiency. Our results show a persistent change in forest structural characteristics along the edges of forest fragments, which resulted in a significantly lower structural diversity, in comparison with the interior of the forest fragments. These structural changes could be observed up to 35 m from the forest edges and are likely to reflect even deeper impacts on other ecosystem variables such as microclimate and biodiversity. Traits related to vertical plant material allocation were more affected than traits related to canopy height. We demonstrate a divergent response from the forest understory (higher vegetation density close to the edge) and the upper canopy (lower vegetation density close to the edge), indicating that assessing forest disturbances using vertically integrated metrics, such as total plant area index, can lead to an erroneous interpretation of no change. Our results demonstrate the strong potential of terrestrial laser scanning for benchmarking broader-scale (e.g. airborne and space-borne) remote sensing assessments of forest disturbances, as well as to provide a more robust interpretation of biophysical changes detected at coarser resolutions.

Above-ground biomass references for urban trees from terrestrial laser scanning data.

Background and AimsWithin extending urban areas, trees serve a multitude of functions (e.g. carbon storage, suppression of air pollution, mitigation of the ‘heat island’ effect, oxygen, shade and recreation). Many of these services are positively correlated with tree size and structure. The quantification of above-ground biomass (AGB) is of especial importance to assess its carbon storage potential. However, quantification of AGB is difficult and the allometries applied are often based on forest trees, which are subject to very different growing conditions, competition and form. In this article we highlight the potential of terrestrial laser scanning (TLS) techniques to extract highly detailed information on urban tree structure and AGB.MethodsFifty-five urban trees distributed over seven cities in Switzerland were measured using TLS and traditional forest inventory techniques before they were felled and weighed. Tree structure, volume and AGB from the TLS point clouds were extracted using quantitative structure modelling. TLS-derived AGB estimates were compared with AGB estimates based on forest tree allometries dependent on diameter at breast height only. The correlations of various tree metrics as AGB predictors were assessed.Key ResultsEstimates of AGB derived by TLS showed good performance when compared with destructively harvested references, with an R2 of 0.954 (RMSE = 556 kg) compared with 0.837 (RMSE = 1159 kg) for allometrically derived AGB estimates. A correlation analysis showed that different TLS-derived wood volume estimates as well as trunk diameters and tree crown metrics show high correlation in describing total wood AGB, outperforming tree height.ConclusionsWood volume estimates based on TLS show high potential to estimate tree AGB independent of tree species, size and form. This allows us to retrieve highly accurate non-destructive AGB estimates that could be used to establish new allometric equations without the need for extensive destructive harvesting.

EVALUATION OF REFLECTANCE FOR BUILDING MATERIALS CLASSIFICATION WITH TERRESTRIAL LASER SCANNER RADIATION

The main purpose of this work is the evaluation of the potential of Terrestrial Laser Scanning (TLS) technology to perform a reflectance analysis of scanned objects. A laser beam, having a coherent beam in the field of visible light (wavelength between 532nm and 680 nm), can lead to optical diffraction phenomena that allow a correlation between the degree of crystallinity of solids (in particular dispersed crystalline materials) and its reflectivity. Different materials with known crystallinity values have been examined and the diffraction value has been analysed for two types of lasers, one pulsed and the other phase measurement, with two different acquisition conditions (nadiral and oblique position). The results demonstrated the correlation by verifying that the incident laser light beam is more refracted by materials with a higher degree of crystallinity than less crystalline or amorphous materials.

Nondestructive Tree Stem and Crown Volume Allometry in Hybrid Poplar Plantations Derived from Terrestrial Laser Scanning

Abstract Accurate and frequently updated tree volume estimates are required for poplar plantations, which are characterized by fast growth rate and short rotation. In this study, we tested the potential of terrestrial laser scanning (TLS) as a reliable method for developing nondestructive tree volume allometries in poplar plantations. The trial was conducted in Italy, where 4- to 10-year-old hybrid plantations were sampled to develop tree crown volume allometry in leaf-on conditions, tree stem volume, and height-diameter allometries in leaf-off conditions. We tested one-entry models based on diameter and two-entry models based on both diameter and height. Model performance was assessed by residual analysis. Results indicate that TLS can provide accurate models of tree stem and crown volume, with percentage of root-mean-square error of about 20 percent and 15 percent, respectively. The inclusion of height does not bring relevant improvement in the models, so that only diameter can be used to predict tree stem and crown volume. The TLS-measured stem volume estimates agreed with an available formula derived from harvesting. We concluded that TLS is a reliable method for developing nondestructive volume allometries in poplar plantations and holds great potential to enhance conventional tree inventory and monitoring. Study Implications: Terrestrial laser scanning (TLS) is a technique that allows nondestructive measurement of the three-dimensional structure of a tree with high precision and low cost. The ability of TLS to measure both tree crown volume and tree position can be effective to test optimal spacing requirements and also to test innovative schemes such as mixed or polycyclic poplar plantations. The spatially explicit nature of TLS measurements allows better integration with different remotely sensed sensors, which can be used in combination with TLS, enabling a multiscale assessment of poplar plantation structure with different levels of detail, enhancing conventional tree inventory and supporting effective management strategies.

Assessing the Effects of Sample Size on Parametrizing a Taper Curve Equation and the Resultant Stem-Volume Estimates

Large and comprehensive datasets, traditionally based on destructive stem analysis or other labor-intensive approaches, are commonly considered as a necessity in developing stem-volume equations. The aim here was to investigate how a decreasing number of sample trees affects parametrizing an existing taper curve equation and resultant stem-volume estimates. Furthermore, the potential of terrestrial laser scanning (TLS) in producing taper curves was examined. A TLS-based taper curve was derived for 246 Scots pines (Pinus sylvestris L.) from southern Finland to parametrize an existing taper curve equation. To assess sensitivity of the parametrization regarding sample size, the number of Scots pines included in the parametrization varied between full census and 1 Scots pine at a time. Root mean square error of stem-volume estimates remained ≤20.9% and the mean absolute difference was relatively constant (≤9.0%) between stem-volume estimates when the sample size included ≥46 Scots pines. Thus, it can be concluded that, with a rather small sample size, a taper curve equation can be re-parametrized for local conditions using point clouds from TLS to produce consistent stem-volume estimates.

International benchmarking of terrestrial laser scanning approaches for forest inventories

The last two decades have witnessed increasing awareness of the potential of terrestrial laser scanning (TLS) in forest applications in both public and commercial sectors, along with tremendous research efforts and progress. It is time to inspect the achievements of and the remaining barriers to TLS-based forest investigations, so further research and application are clearly orientated in operational uses of TLS. In such context, the international TLS benchmarking project was launched in 2014 by the European Spatial Data Research Organization and coordinated by the Finnish Geospatial Research Institute. The main objectives of this benchmarking study are to evaluate the potential of applying TLS in characterizing forests, to clarify the strengths and the weaknesses of TLS as a measure of forest digitization, and to reveal the capability of recent algorithms for tree-attribute extraction. The project is designed to benchmark the TLS algorithms by processing identical TLS datasets for a standardized set of forest attribute criteria and by evaluating the results through a common procedure respecting reliable references. Benchmarking results reflect large variances in estimating accuracies, which were unveiled through the 18 compared algorithms and through the evaluation framework, i.e., forest complexity categories, TLS data acquisition approaches, tree attributes and evaluation procedures. The evaluation framework includes three new criteria proposed in this benchmarking and the algorithm performances are investigated through combining two or more criteria (e.g., the accuracy of the individual tree attributes are inspected in conjunction with plot-level completeness) in order to reveal algorithms’ overall performance. The results also reveal some best available forest attribute estimates at this time, which clarify the status quo of TLS-based forest investigations. Some results are well expected, while some are new, e.g., the variances of estimating accuracies between single-/multi-scan, the principle of the algorithm designs and the possibility of a computer outperforming human operation. With single-scan data, i.e., one hemispherical scan per plot, most of the recent algorithms are capable of achieving stem detection with approximately 75% completeness and 90% correctness in the easy forest stands (easy plots: 600 stems/ha, 20 cm mean DBH). The detection rate decreases when the stem density increases and the average DBH decreases, i.e., 60% completeness with 90% correctness (medium plots: 1000 stem/ha, 15 cm mean DBH) and 30% completeness with 90% correctness (difficult plots: 2000 stems/ha, 10 cm mean DBH). The application of the multi-scan approach, i.e., five scans per plot at the center and four quadrant angles, is more effective in complex stands, increasing the completeness to approximately 90% for medium plots and to approximately 70% for difficult plots, with almost 100% correctness. The results of this benchmarking also show that the TLS-based approaches can provide the estimates of the DBH and the stem curve at a 1–2 cm accuracy that are close to what is required in practical applications, e.g., national forest inventories (NFIs). In terms of algorithm development, a high level of automation is a commonly shared standard, but a bottleneck occurs at stem detection and tree height estimation, especially in multilayer and dense forest stands. The greatest challenge is that even with the multi-scan approach, it is still hard to completely and accurately record stems of all trees in a plot due to the occlusion effects of the trees and bushes in forests. Future development must address the redundant yet incomplete point clouds of forest sample plots and recognize trees more accurately and efficiently. It is worth noting that TLS currently provides the best quality terrestrial point clouds in comparison with all other technologies, meaning that all the benchmarks labeled in this paper can also serve as a reference for other terrestrial point clouds sources.

Terrestrial Laser Scanning to Detect Liana Impact on Forest Structure

Tropical forests are currently experiencing large-scale structural changes, including an increase in liana abundance and biomass. Higher liana abundance results in reduced tree growth and increased tree mortality, possibly playing an important role in the global carbon cycle. Despite the large amount of data currently available on lianas, there are not many quantitative studies on the influence of lianas on the vertical structure of the forest. We study the potential of terrestrial laser scanning (TLS) in detecting and quantifying changes in forest structure after liana cutting using a small scale removal experiment in two plots (removal plot and non-manipulated control plot) in a secondary forest in Panama. We assess the structural changes by comparing the vertical plant profiles and Canopy Height Models (CHMs) between pre-cut and post-cut scans in the removal plot. We show that TLS is able to detect the local structural changes in all the vertical strata of the plot caused by liana removal. Our study demonstrates the reproducibility of the TLS derived metrics for the same location confirming the applicability of TLS for continuous monitoring of liana removal plots to study the long-term impacts of lianas on forest structure. We therefore recommend to use TLS when implementing new large scale liana removal experiments, as the impact of lianas on forest structure will determine the aboveground competition for light between trees and lianas, which has important implications for the global carbon cycle.

Examination of the Potential of Terrestrial Laser Scanning and Structure-from-Motion Photogrammetry for Rapid Nondestructive Field Measurement of Grass Biomass

Above ground biomass (AGB) is a parameter commonly used for assessment of grassland systems. Destructive AGB measurements, although accurate, are time consuming and are not easily undertaken on a repeat basis or over large areas. Structure-from-Motion (SfM) photogrammetry and Terrestrial Laser Scanning (TLS) are two technologies that have the potential to yield precise 3D structural measurements of vegetation quite rapidly. Recent advances have led to the successful application of TLS and SfM in woody biomass estimation, but application in natural grassland systems remains largely untested. The potential of these techniques for AGB estimation is examined considering 11 grass plots with a range of biomass in South Dakota, USA. Volume metrics extracted from the TLS and SfM 3D point clouds, and also conventional disc pasture meter settling heights, were compared to destructively harvested AGB total (grass and litter) and AGB grass plot measurements. Although the disc pasture meter was the most rapid method, it was less effective in AGB estimation (AGBgrass r2 = 0.42, AGBtotal r2 = 0.32) than the TLS (AGBgrass r2 = 0.46, AGBtotal r2 = 0.57) or SfM (AGBgrass r2 = 0.54, AGBtotal r2 = 0.72) which both demonstrated their utility for rapid AGB estimation of grass systems.

Image-based correlation of Laser Scanning point cloud time series for landslide monitoring

Very high resolution monitoring of landslide kinematics is an important aspect for a physical understanding of the failure mechanisms and for quantifying the associated hazard. In the last decade, the potential of Terrestrial Laser Scanning (TLS) to monitor slow-moving landslides has been largely demonstrated but accurate processing methods are still needed to extract useful information available in point cloud time series. This work presents an approach to measure the 3D deformation and displacement patterns from repeated TLS surveys. The method is based on the simplification of a 3D matching problem in a 2D matching problem by using a 2D statistical normalized cross-correlation function. The computed displacement amplitudes are compared to displacements (1) calculated with the classical approach of Iterative Closest Point and (2) measured from repeated dGPS observations. The performance of the method is tested on a 3 years dataset acquired at the Super-Sauze landslide (South French Alps). The observed landslide displacements are heterogeneous in time and space. Within the landslide, sub-areas presenting different deformation patterns (extension, compression) are detected by a strain analysis. It is demonstrated that pore water pressure changes within the landslide is the main controlling factor of the kinematics.

Yersel lazer tarama ile tek ağaç özelliklerinin belirlenmesi

In this study, the potential of Terrestrial Laser Scanning (TLS) data obtained from a single point on determination of some individual tree characteristics was assessed. The study was carried out in two beech stands, two Corsican pine stands, and one Douglas fir stand located in an urban woodland in the North England. The targeted tree attributes including diameter at breast height (DBH), tree height, crown base height, and crown width were determined both by the field measurements and from the laser point cloud data. Totally, we measured the DBH in 127 trees in the beech and Corsican pine plots, and the tree height, crown base height, and crown width were determined in 45 trees in only the Corsican pine plots. However, we were not able to measure any tree attributes on the laser point cloud in the sampling plot taken from Douglas fir stand due to high stand density (1393 trees ha-1). The relationships between field-measured and laser-derived tree attributes were determined using simple regression analyses. The obtained determination coefficients (R2) and root mean square errors (RMSE) were; 0,91 and 5.84 cm for DBH; 0,88 and 1,1 m for tree height; 0,83 and 1 m for crown base height; 0,65 and 0,81 m for crown with, respectively. It was concluded that using laser data obtained from a single scan, a) the DBH in definite rate of individuals might be measured in the forest stands with low density; and similarly in some trees, b) the tree height and the other crown characteristics might be determined in conifer stands with a canopy cover less than 70 percent. Keywords: Lidar, Forest inventory, Stand structure

The potential of terrestrial laser scanning for the estimation of understory biomass in coppice-with-standard systems

Methods for estimating the biomass potential of dense coppice in coppice-with-standard forests in a fast and objective way are currently rare. We adapted existing methodical approaches for biomass estimations from terrestrial laser scanning developed for mature stands in order to perform single scan measurements of diameter at breast height in extremely dense coppice with a stem density of 30,000 ha−1. Diameter was then used as input for allometric regression models for estimations of the dry weights. As a tribute to the dense stocking on the investigated stands study plots were smaller than in previous studies focusing on mature forests. Results were found to be sound with a mean absolute error of about 6.9 kg which is equal to a relative error of 11.1%. With respect to the strongly reduced amount of field work the method is therefore of high efficiency. With the new approach reliable assessments of the bioenergy potentials become possible for coppice stands, which might play an important role in future tasks of mitigating climate change.

Terrestrial laser scanning for measuring the solid wood volume, including branches, of adult standing trees in the forest environment

This study evaluates the potential of terrestrial laser scanning (TLS) to assess the solid wood volume (i.e., stem and branch diameters of more than 7cm) of adult standing trees in the forest environment. The solid wood volume of 42 trees of different species and size classes was investigated under leafless conditions, both by manual destructive field measurements and by TLS. The trees were first digitised by TLS using a protocol developed to provide fine-scale sampling of trees within acceptable scanning time. TLS data were processed by retro-engineering software using geometric fitting procedures to model tree woody structure and to compute the wood volume. After tree felling, labour-intensive fieldwork was conducted to obtain the solid wood volume of the trees by destructive measurements. The comparison between both methods gave excellent results, regardless of the tree species or size. The relative differences of the TLS estimates remained primarily within a range of ±10% for estimating the volume of the main stem of the trees, and within a range of ±30% for estimating the cumulative branch volumes. Although our semi-automated modelling method makes it possible to overcome the effect of (acceptable) wind, it remains time-consuming and requires further improvement to be used on a large number of trees. However, it demonstrates the appropriateness of laser scanning techniques and simple geometric fitting to characterise the woody structure of a tree in the forest environment and provides new insights for tree growth monitoring, carbon sequestration and bioenergy assessment.

Beitrag des terrestrischen Laserscannings zur Erfassung der Struktur von Baumkronen | Application of terrestrial laser scanning for measuring tree crown structures

This paper addresses the potential of terrestrial laser scanning (TLS) for describing and modelling of tree crown structure and dynamics. We first present a general approach for the metabolic and structural scaling of tree crowns. Out of this approach we emphasize those normalization and scaling parameters which become accessible by TLS. For example we show how the individual tree leaf area index, convex hull, and its space-filling by leaves can be extracted out of laser scan data. This contributes to a theoretical and empirical substantiation of crown structure models which were missing so far for e.g. quantification of structural and species diversity in forest stands, inventory of crown biomass, species detection by remote sensing, and understanding of self- and alien-thinning in pure and mixed stands. Up to now works on this topic delivered a rather scattered empirical knowledge mainly by single inventories of trees and stands. In contrast, we recommend to start with a model approach, and to complete existing data with repeated TLS inventories in order to come to a consistent and theoretically based model of tree crowns.

Potential of terrestrial laserscanning in load test measurements of bridges

The state-of-the-art geodetic and remote sensing techniques can prove their potential through particular engineering applications. Besides the traditional surveying terrestrial laserscanning broadens its application field in civil engineering projects. The Department of Photogrammetry and Geoinformatics has long experience in the measurement methods, accuracy analysis and applications of terrestrial laserscanning. This paper deals with the potential of the technology through the examples of load test measurements of Danube bridges. Prior to the particular bridge surveying projects accuracy analysis has been carried out in laboratory measurements, the results validated the accuracy and reliability of the laserscanned data. The paper discusses the complex measurement procedure, the main steps of the data processing and results. Remote sensing can provide data about specific (e.g. with limited accessibility) areas of the structure that cannot be measured with traditional techniques during the short period of the load test measurements. The post-processing includes comparison analysis using ground-based geodetic measurements (such as high precision leveling) as reference in defining displacements. By computing the accuracy measures of the terrestrial laserscanning the overall technology can be qualified and calibrated.