Terrestrial Laser Scanning Surveys Research Articles

Cultural heritage characteristics and damage analysis based on multidimensional data fusion and HBIM–taking the former residence of HSBC bank in Xiamen, China as an example

In the context of digitalizing cultural heritage, HBIM is garnering increasing attention from heritage conservationists for its advantages. In conservation practices for cultural heritage, expressing regional characteristics and documenting in HBIM has become increasingly crucial, and these needs are inextricably linked to the need for models with a high level of detail (LOD). This paper presents a combination of Terrestrial Laser Scanning surveys, UAV photogrammetry, and handheld laser scanning to scan cultural heritage. The scan data obtained from multiple digital surveys serves as the foundation for modelling HBIM. For the regional characteristics, the HBIM model was built with detailed geometric shapes, configurations, materials, and colors of each element, as well as complex patterns and damage using the parametric models and mesh models. The information of the building and its components stored in the HBIM model. Consequently, obtained a highly detailed HBIM that not only captures the intricate details of the ideal state and real-world damage and degradation with minimal error but also serves as a repository for a multitude of information types. It has been concluded that a high LOD is essential to representing the regional geometric feature of a building and recording the damage of cultural heritage.

Degradation of the 2014–2015 Holuhraun vent-proximal edifice in Iceland

AbstractThe earliest stages of volcanic vent degradation are rarely measured, leaving a gap in the knowledge that informs landform degradation models of cinder cones and other monogenetic vent structures. We documented the initial degradation of a 500-m-long spatter rampart at the primary vent of the 2014–2015 Holuhraun eruption in northern Iceland with high-resolution topographic change maps derived from terrestrial laser scanning (TLS) and photogrammetric surveys using an unoccupied aircraft system (UAS). Topographic differencing shows a total negative volume change of 42,637 m3, and a total positive volume change (basal deposition) of 10,304 m3 (primarily as deposition at the base of steeply sloping surfaces). Two distinct styles of volume changes were observed on the interior and exterior of the spatter rampart. Material on the interior of the vent was removed from oversteepened slopes by discrete rockfalls, while diffusive processes were qualitatively evident on the exterior slopes. We propose a novel conceptual landform evolution model for spatter ramparts that combines rockfall processes on the interior walls, diffusive gravitational sliding on the exterior slopes, and incorporates cooling contraction and compaction over the entire edifice to describe the observed modes of topographic change during the onset of degradation. Potential hazards at fresh spatter ramparts are rockfalls at high slope areas of the vent interior walls where contacts between spatter clasts are prone to weakening by fumarolic activity, weathering, and settling. To capture such hazards, our data suggest a cadence for monitoring changes yearly for the first few years post-eruption, and at longer intervals thereafter.

Terrestrial laser scanning vs. manual methods for assessing complex forest stand structure: a comparative analysis on plenter forests

In continuous cover forestry, plenter silviculture is regarded as an elaborated system for optimizing the sustainable production of high-quality timber maintaining a constant but heterogeneous canopy. Its complexity necessitates high silvicultural expertise and a detailed assessment of forest stand structural variables. Terrestrial laser scanning (TLS) can offer reliable techniques for long-term tree mapping, volume calculation, and stand variables assessment in complex forest structures. We conducted surveys using both automated TLS and conventional manual methods (CMM) on two plots with contrasting silvicultural regimes within the Black Forest, Germany. Variations in automated tree detection and stand variables were greater between different TLS surveys than with CMM. TLS detected an average of 523 tree stems per hectare, while CMM counted 516. Approximately 9.6% of trees identified with TLS were commission errors, with 6.5% of CMM trees being omitted using TLS. Basal area per hectare was slightly higher in TLS (38.9 m3) than in CMM (38.2 m3). However, CMM recorded a greater standing volume (492.7 m3) than TLS (440.5 m3). The discrepancy in stand volume between methods was primarily due to TLS underestimating tree height, especially for taller trees. DBH bias was minor at 1 cm between methods. Repeated TLS inventories successfully matched an average of 424 tree positions per hectare. While TLS adequately characterizes complex plenter forest structures, we propose enhancing this methodology with personal laser scanning to optimize crown coverage and efficiency and direct volume measurements for increased accuracy of wood volume estimations. Additionally, utilizing 3D point cloud data-derived metrics, such as structural complexity indices, can further enhance plenter forest management.

Similarity and Change Detection of Relief in a Proglacial River Valley (Scott River, SW Svalbard)

This study focuses on contemporary geomorphic changes in the proglacial valley floor of the Scott River catchment (northwest of Wedel Jarlsberg Land, southwestern Spitsbergen). The similarity and variability of landforms along the entire 3.3 km length of the unglaciated valley floor was assessed using precision terrestrial laser scanning (TLS) measurements made in July/August 2010–2013. Digital terrain models (DTMs) were generated from the high-resolution TLS survey data, followed by a geomorphon map, which was then used for a similarity and changes of morphology analysis performed with GeoPAT2 software. The study revealed a large spatial variation of contemporary processes shaping the valley floor and changes in its morphology. Their spatial distribution relates to the geologically determined split of the valley floor into three morphological zones separated by gorges. The upper gorge cuts the terminal moraine rampart, which limits the uppermost section of the valley floor, which is up to 700 m wide and is occupied by the outwash plain. The study showed that this is the area characterised by the greatest dynamics of contemporary geomorphic processes and relief changes. The similarity index value here is characterised by a large spatial variation that in some places reaches values close to 0. In the middle section stretching between the upper gorge (cutting the terminal moraine) and the lower gorge (cutting the elevated marine terraces), a much smaller variability of processes and landforms is observed, and the found changes of the valley floor relief mainly include the area of braided channel activity. Similarity index values in this zone do not fall below 0.65. The lowest section, the mouth of the alluvial fan, on the other hand, is characterised by considerable spatial differentiation. The southern part of the fan is stable, while the northern part is intensively re-shaped and has a similarity index that locally falls below 0.5. The most dynamic changes are found within the active channel system along the entire length of the unglaciated section of the Scott River. The peripheral areas, located in the outer zones of the valley floor, show great stability.

Object positional uncertainty modelling in 2D viewpoint planning

Viewpoint planning of terrestrial laser scanning surveys is often guided by the level of accuracy, which is a measure of radiated point precision that does not account for all factors affecting positional uncertainty. We propose the use of modelled object precision for viewpoint planning in a methodology that rigorously combines the three sources of positional uncertainty: the observations; registration; and the observation distribution. Our method is demonstrated on three 2D datasets by analyzing object precision in comparison to United States General Services Administration accuracy criterion. The results show the method's ability to 1) represent the precision for all objects in the environment; 2) identify problem areas where the level of accuracy specification is not met; and 3) inform densification measures needed to improve the design. Detailed explanations of the causes of design weaknesses accompany the results to illustrate the challenges of scanning complex built environments and to highlight solutions.

THE EUROSDR RPAS BENCHMARK: OPEN DATASET DESCRIPTION AND SUMMARY OF KEY RESULTS

Abstract. In 2021 EuroSDR initiated a benchmark study with the aim to evaluate the geometric quality of real-world survey data generated from state-of-practice commercial Remotely Piloted Aircraft System (RPAS) photogrammetry (including DJI P4 RTK and DJI P1) and lidar (including DJI L1 and Riegl MiniVUX). The particular benchmark focus was on achievable data quality from real-world network configurations in the absence of ground control, on-the-fly Real Time Kinematic (RTK) corrections, and/or local GNSS base station information. Successive custom datasets were released to registered benchmark participants who submitted individual outputs that were independently evaluated against reference surveys. Without the inclusion of any supporting ground information, DJI P4 RTK and DJI P1 RPAS solutions were found to deliver m- and dm-level accuracies, respectively, in both plan and height. RTK solutions were found to provide cm-level precisions and accuracies, with some outliers. The introduction of ground control points resulted in similar planimetric accuracy to the RTK solutions, but with slight improvements in height. In terms of lidar datasets, the Riegl MiniVUX solution, using corrections from a local base station, was found to provide smaller discrepancies than the DJI L1 RTK solution, when independently compared against terrestrial laser scanning surveys. This paper provides various quality statistics and demonstrates multiple ways of assessing the geometric quality of RPAS data. The EuroSDR RPAS benchmark datasets are now openly available online in order to support and facilitate further investigation by the community.

UNDERGROUND HERITAGE DOCUMENTATION: THE CASE STUDY OF GROTTA ZINZULUSA IN CASTRO (LECCE-ITALY)

Abstract. 3D documentation of the Underground Built Heritage (UBH) is always fundamental for knowledge, management, conservation, and enhancement of cultural heritage, but the challenges involved in documenting this kind of site are many and various, With the aim of providing an accurate and reliable representation of the surveyed area without employing time-consuming processes, Mobile Mapping Systems (MMSs) based on SLAM (Simultaneous Localization And Mapping) technology have now the potential to overcome these challenges, proving to be a useful alternative to traditional surveying techniques. The underground site of Grotta Zinzulusa in Castro (LE), Italy, is an anchialine cave system difficult to access and document due to its narrow passages, large rooms, and poor illumination. Within this case study, the effectiveness of using an MMS approach, employing the STONEX® X120GO SLAM Laser Scanner system, to document the cave system and integrates the data with those obtained from other traditional geomatics techniques, such as UAS (Uncrewed Aerial System) and TLS (Terrestrial Laser Scanning) surveys, has been proved. The study aims to define the best practices and operational methodologies for enhancing the speediness, usability, and cost-effectiveness of using MMSs in underground settings for 3D documentation of heritage sites to provide metrically correct and accurate products for researchers, scientists, and the wider public.

COMPARATIVE ANALYSIS OF POINT CLOUDS ACQUIRED FROM A TLS SURVEY AND A 3D VIRTUAL TOUR FOR HBIM DEVELOPMENT

Abstract. This paper presents a comparative analysis of point clouds acquired from a terrestrial laser scanner (TLS) survey and a 3D virtual tour using Matterport technology for heritage building information modeling (HBIM) development. The study uses the Cloister of the Royal College of Corpus Christi Seminary, an important cultural heritage site in Valencia, Spain, as a case study. The point clouds from the TLS survey and Matterport scans were compared both quantitively in CloudCompare software and visually to assess their accuracy and quality. The Matterport point cloud data was found to be slightly lower in quality and accuracy compared to the TLS data, but still sufficient for developing some low-tolerance geometry in the HBIM model. The study shows that Matterport point cloud data has potential to supplement TLS scans, particularly in areas missed during the TLS survey due to range limitations. Matterport technology is accessible, affordable, and easy to use, making it a feasible option for heritage sites with limited resources. Moreover, Matterport technology captures high-quality visual data, including color and texture, providing a detailed representation of the heritage site. Thus, Matterport technology can be a valuable contribution to cultural heritage documentation and preservation, particularly for sites requiring a quick and efficient surveying process. The findings of this research offer insights into the relative advantages and limitations of these two reality capture techniques for cultural heritage documentation and preservation, and could potentially inform decision-making processes for future heritage preservation projects.

DOCUMENTATION OF COMPLEX ENVIRONMENTS IN CULTURAL HERITAGE SITES. A SLAM-BASED SURVEY IN THE CASTELLO DEL VALENTINO BASEMENT

Abstract. Underground Built Heritage (UBH) stands out among the existing Cultural Heritage sites as a peculiar scenario. The assets belonging to this type of heritage are typically difficult to manage, exploit, and promote because of a lack of knowledge and documentation. The challenges in documenting built heritage are many and wide-ranging, and the main need must be to provide an accurate and appropriate representation of the surveyed area and its geometric features without employing time-consuming processes. Mobile Mapping Systems (MMSs) are nowadays trending technologies for the geomatics community, proving to be a useful alternative to traditional surveying techniques when taking time and cost constraints into account.The paper focuses on the use of an MMS, the STONEX® X120GO SLAM Laser Scanner system, in documenting a portion of the Castello del Valentino, an articulated and complex architecture located in Turin (Italy). The underground floor of the castle, due to its complexity in terms of accessibility and the challenge it poses for the documentation approach, was chosen as a case study to assess the STONEX® X120GO's capabilities in terms of portability of the instrument, speed of acquisition, as well as completeness and accuracy of the acquired dataset. The results obtained using the MMS technique have been compared to and validated using data from a TLS (Terrestrial Laser Scanner) survey used as a ground reference. The results and considerations reported in this paper demonstrate that MMSs can accurately and completely depict built spaces and their main characteristics and have substantial potential in mapping complex assets.

Static Terrestrial Laser Scanning (TLS) for Heritage Building Information Modeling (HBIM): A Systematic Review

Heritage Building Information Modeling (HBIM) is an essential technology for heritage documentation, conservation, and management. It enables people to understand, archive, advertise, and virtually reconstruct their built heritage. Creating highly accurate HBIM models requires the use of several reality capture tools, such as terrestrial laser scanning (TLS), photogrammetry, unmanned aerial vehicles (UAV), etc. However, the existing literature did not explicitly review the applications and impacts of TLS in implementing HBIM. This paper uses the PRISMA protocol to present a systematic review of TLS utilization in capturing reality data in order to recognize the status of applications of TLS for HBIM and identify the knowledge gaps on the topic. A thorough examination of the 58 selected articles revealed the state-of-the-art practices when utilizing static TLS technology for surveying and processing captured TLS data for developing HBIM models. Moreover, the absence of guidelines for using static TLS surveys for HBIM data acquisition, the lack of robust automated frameworks for producing/transferring 3D geometries and their attributes from TLS data to BIM entities, and the under-utilized application of TLS for long-term monitoring and change detection were identified as gaps in knowledge. The findings of this research provide stakeholders with a good grasp of static TLS for HBIM and therefore lay the foundation for further research, strategies, and scientific solutions for improving the utilization of TLS when documenting heritage structures and developing HBIM.

Comparative analysis of Road Scanning Techniques

A three-dimensional road point cloud is not only useful for civil engineers (road rehabilitation, road condition assessment) but can also be useful for vehicle engineers (autonomous vehicle driving scenario, vehicle dynamics simulation). Currently, there are several scanning techniques can be used to obtain these point clouds, such as terrestrial laser scanning (TLS), mobile laser scanning (MLS), airborne laser scanning (ALS), unmanned aerial vehicle (UAV) photogrammetry or UAV laser scanning. This paper discusses the investigation of four road surface scanning techniques by comparing their point clouds and the derived products. The comparison was performed for a section of a road with 1136 m length and 4 m width, the TLS survey provided the reference data. Aspects of point cloud evaluation included geometric accuracy, density, and the parameters of plane-fitting. CRG models were created from all studied point clouds to compare the difference between the final products to be used by the automotive industry. The results show that the MLS and the UAV photogrammetry generated the most accurate point cloud, while UAV laser scanning accuracy was the lowest. Similarly, the CRG models comparison showed that there was no significant difference between MLS and TLS models, and the UAV photogrammetry gave a smoother variation relative to the reference surface. Whereas the largest differences were noted for the CRG model derived from the UAV laser scanning models.
 

Исследование точности построения цифровой модели рельефа в зависимости от плотности наземного лазерного сканирования

The authors discuss the course of processing the terrestrial laser scanning survey data (TLS). The aim of the study is to assess the accuracy of creating digital elevation models (DEMs) depending on the scanning step. As initial data, a stitched and oriented cloud of points of the surveyed surface in the territory of the industrial site was taken; it was subsequently used to create digital elevation models using the TIN method. At the next stage of the study, 6 surveys with different scanning steps (from 0,3 m to 5 m) were artificially simulated in the Cyclone software; after that a comparative analysis of the obtained DEMs building accuracy was carried out. The main indicator of model precision is the root-mean-square deviation (RMSD). In the course of the study, the quality of making a digital elevation models was assessed and the dependence of the surface construction error on the increase in the scanning step was determined.

Accurate deformation analysis based on point position uncertainty estimation and adaptive projection point cloud comparison

The accuracy of the scanning scene representation and corresponding points extraction are key factors in deformation analysis based on point cloud. Still, little is known about the influence of terrestrial laser scanner (TLS) survey properties on point cloud. In our study, an accurate deformation analysis method based on point position uncertainty estimation and adaptive projection point cloud comparison is proposed, which consists of two parts: (1) Evaluating the influence of scanning geometry on point cloud quality to gain high accuracy points; (2) an adaptive projection radius and depth point cloud comparison algorithm is constructed for acquiring corresponding points and calculating the deformation. A regular geometry and a landslide point cloud are selected. Results show that the mean error and mean absolute deviation of the distance between corresponding points are –0.3 mm and 16.2 mm, which demonstrates the method can provide an effective solution for the deformation analysis of complex topography.

Expeditious Low-Cost SfM Photogrammetry and a TLS Survey for the Structural Analysis of Illasi Castle (Italy)

The structural analysis of degraded historical buildings requires an adequate 3D model of the object. Structure from motion (SfM) photogrammetry and laser scanning geomatics techniques can satisfy this request by providing geometrically affordable data. The accuracy and resolution depend on the instruments and procedures used to extract the 3D models. This work focused on a 3D survey of Illasi Castle, a strongly degraded historical building located in northern Italy, aimed at structural analysis in the prevision of a static recovery. A low-cost drone, a single-lens reflex (SLR) camera, and a smartphone were used in the survey. From each acquired dataset, using the integration between the images acquired by the drone and the SLR camera, a 3D model of the building was extracted by means of the SfM technique. The data were compared with high-precision and high-resolution terrestrial laser scanning (TLS) acquisitions to evaluate the accuracy and performance of the fast and low-cost SfM approach. The results showed a standard deviation value for the point cloud comparisons in the order of 2–3 cm for the best solution (integrating drone and SLR images) and 4–7 cm using smartphone images. Finally, the integration of the best SfM model of the external walls and the TLS model of the internal portion of the building was used in finite element (FE) analysis to provide a safety assessment of the structure.

Morphology, flow dynamics and evolution of englacial conduits in cold ice

AbstractMeltwater routing through ice masses exerts a fundamental control over glacier dynamics and mass balance, and proglacial hydrology. However, despite recent advances in mapping drainage systems in cold, Arctic glaciers, direct observations of englacial channels and their flow conditions remain sparse. Here, using terrestrial laser scanning (TLS) surveys of the main englacial channel of cold‐based Austre Brøggerbreen (Svalbard), we map and compare an entrance moulin reach (122 m long) and exit portal reach (273 m long). Analysis of channel planforms, longitudinal profiles, cross‐sections and morphological features reveals evidence of spatial variations in water flow conditions and channel incision mechanisms, and the presence of vadose, epiphreatic and phreatic conditions. The entrance reach, located at the base of a perennial moulin, was characterized by vadose, uniform, channel lowering at annual timescales, evidenced by longitudinal grooves, whereas the exit portal reach showed both epiphreatic and vadose conditions, along with upstream knickpoint migration at intra‐annual timescales. Fine‐scale features, including grooves and scallops, were readily quantified from the TLS point cloud, highlighting the capacity of the technique to inform palaeoflow conditions, and reveal how pulses of meltwater from rainfall events may adjust englacial conduit behaviour. With forecasts of increasing Arctic precipitation in the coming decades, and a progressively greater proportion of glaciers comprising cold ice, augmenting the current knowledge of englacial channel morphology is essential to constrain future glacier hydrological system change.

Study of Point Cloud Integration between UAV-based Dataset and Aerial LiDAR Survey

The migration of Photogrammetry from the analog medium to the digital medium changed how photogrammetric surveys were carried out and how data are processed, allowing the automation of several steps used in the photogrammetric design workflow. There is extensive research in cartographic and geodetic sciences, involving the acquisition of data through photogrammetry, and through techniques such as Structure from Motion (SfM) and Laser Scanner survey. Such research and work involve the use of point clouds from Unmanned Aerial Vehicle (UAV) photogrammetric surveys and Terrestrial Laser Scanner (TLS) surveys, as well as the fusion of these point clouds. This work aims to study the integration of an aerial LiDAR point cloud with a Photogrammetric Point Cloud (PPC) from the UAV survey to minimize occlusion failures and building edges, densify the point cloud, and reduce spurious points. Statistical analyses were performed for the refinement, adjustment, and integration between the point clouds. The results showed that the correction map generated for integrating the clouds reached the objective proposed in this work. The integration of clouds increased from 7 pts/m² of the cloud coming from LiDAR to 140 pts/m² in the final.

Laser Scanning Investigation and Geophysical Monitoring to Characterise Cultural Heritage Current State and Threat by Traffic-Induce Vibrations: The Villa Farnesina in Rome

A multidisciplinary approach is often the only way to assess the state of the cultural heritage, thus involving different specialist expertise and techniques. The paper shows the paired use of terrestrial laser scanning (TLS) and geophysical monitoring (GM) to detect past effects and analyse the actual vibration levels induced by traffic on cultural heritage. The case study is the Villa Farnesina, one of the most important Renaissance buildings commissioned by the banker Agostino Chigi. The Villa contains frescoes attributed to Raphael and other famous 16th century artists, and it is located a few meters from the Lungotevere, which is one of the busiest roads in the historic centre of Rome. Testimonies report the damages caused by the construction of the embankment of the Tiber River, as well as by the traffic in the second half of the 20th century, so much so as to require requalification of the road artery. The TLS survey allows for detecting cracks and deteriorations of the frescoes, although these were subjected to restoration activities over the time, whereas the (GM) allows analysing actual vibrations induced by traffic at the different floors and outside the Villa. Although the measured vibration limits, as velocity peaks in defined frequency ranges, are below the thresholds established by international codes, the importance of the wall paintings and their already-shown susceptibility to damage suggest keeping the building under constant monitoring.

Kinematics and geomorphological changes of a destabilising rock glacier captured from close-range sensing techniques (Tsarmine rock glacier, Western Swiss Alps)

Accurately assessing landform evolution and quantifying rapid environmental changes are gaining importance in the context of monitoring techniques in alpine environments. In the European Alps, glaciers and rock glaciers are among the most characteristic cryospheric components bearing long and systematic monitoring periods. The acceleration in rock glacier velocities and the onset of destabilization processes, mainly since 1990, have raised several concerns due to the potential effects on the high alpine natural and anthropic environments. This study presents a combination of uncrewed aerial vehicle (UAV) and terrestrial laser scanning (TLS) surveys for monitoring the current changes on the quickly accelerating, destabilised Tsarmine rock glacier in the Arolla Valley, Western Swiss Alps, delivering a considerable volume of debris to a steep torrential gully. High-resolution digital elevation models (DEMs) and orthomosaics are derived from UAV image series combined with structure from motion (SfM) photogrammetry techniques. Multitemporal orthomosaics are employed for measuring spatially continuous rock glacier kinematics using image matching algorithms. Superficial displacements are evaluated with simultaneousin-situdifferential global navigation satellite system (GNSS) measurements. Elevation and volume changes are computed from TLS and UAV-derived DEMs at similar periods. Between June 2017 and September 2019, both datasets showed a similar elevation change pattern and surface thinning rates of 0.15 ± 0.04 and 0.16 ± 0.03 m yr−1, respectively. Downward of a rupture zone developing about 150 m above the front, the rock glacier doubled its overall velocity during the study period, from around 5 m yr−1between October 2016 and June 2017 to more than 10 m yr−1between June and September 2019. The kinematic information reveals striking differences in the velocity between the lower and upper rock glacier sections. The monitoring approach based on close-sensing techniques provides accurate surface velocity and volume change information, allowing an enhanced description of the current rock glacier dynamics and its surface expression.

Observation distribution modelling and closed-from precision estimation of scanned 2D geometric features for network design

Geometric features such as cylinders and planes are important objects of interest in terrestrial laser scanner surveys of complex scenes. The quality of the objects modelled from the laser scanner data is a function of many variables and geometric network design plays a key role in maximizing precision. The expected precision can be predicted at the planning stage from simulations of the environment to be scanned. However, this practice can incur a high computational load, even if performed in 2D rather than in 3D. In this paper, a closed-form solution to estimate geometric object precision is proposed as an efficient first order network design tool. It models the laser scanner measurement process with an observation distribution function that is introduced into the least-squares normal equations. Parameter precision is evaluated directly by solving a few (three to six) integrals and inverting the normal equations matrix. The method is presented for two cases of a circle lying in the horizontal plane and a 2D line scanned from a single location. Both a simplified circle model and a more general circle model are explored. The method is then extended using the summation of normals method to allow precision estimation from the combination of multiple scans from different locations. Results from many real datasets, 95 circles and 30 lines, show that the distributions of the range observations and derived Cartesian coordinates follow model predictions. Moreover, results demonstrate that the method can predict circle parameter standard deviations within 4%–6% of the experimental values. The agreement is at the 10% level for a very specific case due to inherent high parameter correlation. The agreement of line parameter standard deviations is much greater, approximately 0.1%. The results show the method can be a valuable tool to predict feature quality with minimal computational requirements. The method is beneficial to not only laser scanner network design but could also be to instantaneous 2D map construction performed for SLAM-based surveys.

Timely and Low-Cost Remote Sensing Practices for the Assessment of Landslide Activity in the Service of Hazard Management

Landslides are among the most dangerous and catastrophic events in the world. The increasing progress in remote sensing technology made landslide observations timely, systematic and less costly. In this context, we collected multi-dated data obtained by Unmanned Aerial Vehicle (UAV) campaigns and Terrestrial Laser Scanning (TLS) surveys for the accurate and immediate monitoring of a landslide located in a steep and v-shaped valley, in order to provide operational information concerning the stability of the area to the local authorities. The derived data were processed appropriately, and UAV-based as well as TLS point clouds were generated. The monitoring and assessment of the evolution of the landslide were based on the identification of instability phenomena between the multi-dated UAV and TLS point clouds using the direct cloud-to-cloud comparison and the estimation of the deviation between surface sections. The overall evaluation of the results revealed that the landslide remains active for three years but is progressing particularly slowly. Moreover, point clouds arising from a UAV or a TLS sensor can be effectively utilized for landslide monitoring with comparable accuracies. Nevertheless, TLS point clouds proved to be denser and more appropriate in terms of enhancing the accuracy of the monitoring process. The outcomes were validated using measurements, acquired by the Global Navigation Satellite System (GNSS).