scholarly journals Measurement of rock glacier surface change over different timescales using terrestrial laser scanning point clouds

2021 ◽  
Vol 9 (1) ◽  
pp. 19-28
Author(s):  
Veit Ulrich ◽  
Jack G. Williams ◽  
Vivien Zahs ◽  
Katharina Anders ◽  
Stefan Hecht ◽  
...  
Keyword(s):  
Laser Scanning ◽  
Point Clouds ◽  
Rock Glacier ◽  
Glacier Surface ◽  
Terrestrial Lidar ◽  
Surface Change ◽  
Relative Contribution ◽  
Time Period ◽  
Multiple Processes ◽  
Glacier Flow

Abstract. Topographic change at a given location usually results from multiple processes operating over different timescales. However, interpretations of surface change are often based upon single values of movement, measured over a specified time period or in a single direction. This work presents a method to help separate surface change types that occur at different timescales related to the deformation of an active rock glacier, drawing on terrestrial lidar monitoring at sub-monthly intervals. To this end, we derive 3D topographic changes across the Äußeres Hochebenkar rock glacier in the Ötztal Alps. These changes are presented as the relative contribution of surface change during a 3-week period (2018) to the annual surface change (2017–2018). They are also separated according to the spatially variable direction perpendicular to the local rock glacier surface (using point cloud distance computation) and a single main direction of rock glacier flow, indicated by movement of individual boulders. In a 1500 m2 sample area in the lower tongue section of the rock glacier, the contribution of the 3-week period to the annual change perpendicular to the surface is 20 %, compared with 6 % in the direction of rock glacier flow. Viewing change in this way, our approach provides estimates of surface change in different directions that are dominant at different times of the year. Our results demonstrate the benefit of more frequent lidar monitoring and, critically, the requirement for novel approaches to quantifying and disaggregating surface change, as a step towards rock glacier observation networks focusing on the analysis of 3D surface change over time.

scholarly journals Disaggregating surface change mechanisms of a rock glacier using terrestrial laser scanning point clouds acquired at different time scales

2020 ◽  
Author(s):  
Veit Ulrich ◽  
Jack G. Williams ◽  
Vivien Zahs ◽  
Katharina Anders ◽  
Stefan Hecht ◽  
...  
Keyword(s):  
Laser Scanning ◽  
Point Clouds ◽  
Rock Glacier ◽  
Glacier Surface ◽  
Terrestrial Lidar ◽  
Surface Change ◽  
Relative Contribution ◽  
Rock Glaciers ◽  
Change Mechanisms ◽  
Glacier Flow

Abstract. Topographic change at a given location usually results from multiple processes operating over different timescales. However, interpretations of surface change are often based upon single values of movement, measured over a specified time period and in a single direction. This work presents a method to help separate surface change mechanisms related to the deformation of an active rock glacier, drawing on terrestrial lidar monitoring at sub-monthly intervals. We derive 3D topographic changes across the Äußeres Hochebenkar rock glacier in the Ötztal Alps. These are presented as the relative contribution of surface change during a three-week period of snow-free conditions (2018) to the annual surface change (2017–2018). They are also separated according to the direction perpendicular to the local rock glacier surface (using point cloud distance computation) and the direction of rock glacier flow, indicated by movement of individual boulders. In a 1500 m2 sample area in the lower tongue section of the rock glacier, the contribution of the three-week period to the annual change perpendicular to the surface is 20 %, as compared to 6 % in the direction of rock glacier flow. This shows that different directions of surface change are dominant at different times of the year. Our results demonstrate the benefit of more frequent lidar monitoring and, critically, the requirement of novel approaches to detecting change, as a step towards interpreting the mechanisms that underlie the surface change of rock glaciers.

scholarly journals Toward a Novel Laser-Based Approach for Estimating Snow Interception

2020 ◽  
Vol 12 (7) ◽  
pp. 1146 ◽  
Author(s):  
Micah Russell ◽  
Jan U. H. Eitel ◽  
Andrew J. Maguire ◽  
Timothy E. Link
Keyword(s):  
Laser Scanning ◽  
Three Dimensional ◽  
Point Clouds ◽  
Primary Objective ◽  
Snow Accumulation ◽  
Future Research ◽  
Snow Density ◽  
Canopy Interception ◽  
Terrestrial Lidar ◽  
Large Trees

Forests reduce snow accumulation on the ground through canopy interception and subsequent evaporative losses. To understand snow interception and associated hydrological processes, studies have typically relied on resource-intensive point scale measurements derived from weighed trees or indirect measurements that compared snow accumulation between forested sites and nearby clearings. Weighed trees are limited to small or medium-sized trees, and indirect comparisons can be confounded by wind redistribution of snow, branch unloading, and clearing size. A potential alternative method could use terrestrial lidar (light detection and ranging) because three-dimensional lidar point clouds can be generated for any size tree and can be utilized to calculate volume of the intercepted snow. The primary objective of this study was to provide a feasibility assessment for estimating snow interception volume with terrestrial laser scanning (TLS), providing information on challenges and opportunities for future research. During the winters of 2017 and 2018, intercepted snow masses were continuously measured for two model trees suspended from load-cells. Simultaneously, autonomous terrestrial lidar scanning (ATLS) was used to develop volumetric estimates of intercepted snow. Multiplying ATLS volume estimates by snow density estimates (derived from empirical models based on air temperature) enabled the comparison of predicted vs. measured snow mass. Results indicate agreement between predicted and measured values (R2 ≥ 0.69, RMSE ≥ 0.91 kg, slope ≥ 0.97, intercept ≥ −1.39) when multiplying TLS snow interception volume with a constant snow density estimate. These results suggest that TLS might be a viable alternative to traditional approaches for mapping snow interception, potentially useful for estimating snow loads on large trees, collecting data in difficult to access terrain, and calibrating snow interception models to new forest types around the globe.

scholarly journals GEOMATIC METHODS APPLIED TO THE CHANGE STUDY OF THE LA PAÚL ROCK GLACIER, SPANISH PYRENEES

2019 ◽  
Vol XLII-2/W13 ◽  
pp. 1771-1775
Author(s):  
A. Martínez-Fernández ◽  
E. Serrano ◽  
J. J. Sanjosé ◽  
M. Gómez-Lende ◽  
A. Pisabarro ◽  
...  
Keyword(s):  
Laser Scanning ◽  
Satellite System ◽  
Ice Age ◽  
Rock Glacier ◽  
Glacier Surface ◽  
The North ◽  
Spanish Pyrenees ◽  
Gnss Receivers ◽  
Rock Glaciers ◽  
Global Navigation Satellite

<p><strong>Abstract.</strong> Rock glaciers are one of the most important features of the mountain permafrost in the Pyrenees. La Paúl is an active rock glacier located in the north face of the Posets massif in the La Paúl glacier cirque (Spanish Pyrenees). This study presents the preliminary results of the La Paúl rock glacier monitoring works carried out through two geomatic technologies since 2013: Global Navigation Satellite System (GNSS) receivers and Terrestrial Laser Scanning (TLS) devices. Displacements measured on the rock glacier surface have demonstrated both the activity of the rock glacier and the utility of this equipment for the rock glaciers dynamic analysis. The glacier has exhibited the fastest displacements on its west side (over 35&amp;thinsp;cm&amp;thinsp;yr<sup>&amp;minus;1</sup>), affected by the Little Ice Age, and frontal area (over 25&amp;thinsp;cm&amp;thinsp;yr<sup>&amp;minus;1</sup>). As an indicator of permafrost in marginal environments and its peculiar morphology, La Paúl rock glacier encourages a more prolonged study and to the application of more geomatic techniques for its detailed analysis.</p>

scholarly journals Detecting Short-Term Surface Melt on an Arctic Glacier Using UAV Surveys

2018 ◽  
Vol 10 (10) ◽  
pp. 1547 ◽  
Author(s):  
Eleanor Bash ◽  
Brian Moorman ◽  
Allison Gunther
Keyword(s):  
Mass Balance ◽  
Point Clouds ◽  
Glacier Mass Balance ◽  
Short Term ◽  
Glacier Surface ◽  
Surface Change ◽  
Glacier Ice ◽  
Arctic Glacier ◽  
Surface Changes

Current understanding of glacier mass balance changes under changing climate is limited by scarcity of in situ measurements in both time and space, as well as resolution of remote sensing products. Recent innovations in unmanned aerial vehicles (UAVs), as well as structure-from-motion photogrammetry (SfM), have led to increased use of digital imagery to derive topographic data in great detail in many fields, including glaciology. This study tested the capability of UAV surveys to detect surface changes over glacier ice during a three-day period in July 2016. Three UAV imaging missions were conducted during this time over 0.185 km 2 of the ablation area of Fountain Glacier, NU. These were processed with the SfM algorithms in Agisoft Photoscan Professional and overall accuracies of the resulting point clouds ranged from 0.030 to 0.043 m. The high accuracy of point clouds achieved here is primarily a result of a small ground sampling distance (0.018 m), and is also influenced by GPS precision. Glacier surface change was measured through differencing of point clouds and change was compared to ablation stake measurements. Surface change measured with the UAV-SfM method agreed with the coincident ablation stake measurements in most instances, with RMSE values of 0.033, 0.028, and 0.042 m for one-, two-, and three-day periods, respectively. Total specific melt over the study area measured with the UAV was 0.170 m water equivalent (w.e.), while interpolation of ablation measurements resulted in 0.144 m w.e. Using UAVs to measure small changes in glacier surfaces will allow for new investigations of distribution of mass balance measurements.

scholarly journals Assessing the applicability of terrestrial laser scanning for mapping englacial conduits

2017 ◽  
Vol 64 (243) ◽  
pp. 37-48 ◽  
Author(s):  
J. E. KAMINTZIS ◽  
J. P. P. JONES ◽  
T. D. L. IRVINE-FYNN ◽  
T. O. HOLT ◽  
P. BUNTING ◽  
...  
Keyword(s):  
Cross Section ◽  
Laser Scanning ◽  
Temporal Evolution ◽  
Terrestrial Laser Scanning ◽  
Point Clouds ◽  
Glacier Surface ◽  
Channel Geometry ◽  
Direct Observations ◽  
Drainage Networks ◽  
Shaped Cross Section

ABSTRACTThe morphology of englacial drainage networks and their temporal evolution are poorly characterised, particularly within cold ice masses. At present, direct observations of englacial channels are restricted in both spatial and temporal resolution. Through novel use of a terrestrial laser scanning (TLS) system, the interior geometry of an englacial channel in Austre Brøggerbreen, Svalbard, was reconstructed and mapped. Twenty-eight laser scan surveys were conducted in March 2016, capturing the glacier surface around a moulin entrance and the uppermost 122 m reach of the adjoining conduit. The resulting point clouds provide detailed 3-D visualisation of the channel with point accuracy of 6.54 mm, despite low (<60%) overall laser returns as a result of the physical and optical properties of the clean ice, snow, hoar frost and sediment surfaces forming the conduit interior. These point clouds are used to map the conduit morphology, enabling extraction of millimetre-to-centimetre scale geometric measurements. The conduit meanders at a depth of 48 m, with a sinuosity of 2.7, exhibiting teardrop shaped cross-section morphology. This improvement upon traditional surveying techniques demonstrates the potential of TLS as an investigative tool to elucidate the nature of glacier hydrological networks, through reconstruction of channel geometry and wall composition.

scholarly journals Tree Biomass Equations from Terrestrial LiDAR: A Case Study in Guyana

Forests ◽  
2019 ◽  
Vol 10 (6) ◽  
pp. 527 ◽  
Author(s):  
Alvaro Lau ◽  
Kim Calders ◽  
Harm Bartholomeus ◽  
Christopher Martius ◽  
Pasi Raumonen ◽  
...  
Keyword(s):  
Laser Scanning ◽  
Tree Height ◽  
Point Clouds ◽  
Validation Data ◽  
Terrestrial Lidar ◽  
Allometric Models ◽  
Crown Diameter ◽  
National Monitoring ◽  
Large Trees

Large uncertainties in tree and forest carbon estimates weaken national efforts to accurately estimate aboveground biomass (AGB) for their national monitoring, measurement, reporting and verification system. Allometric equations to estimate biomass have improved, but remain limited. They rely on destructive sampling; large trees are under-represented in the data used to create them; and they cannot always be applied to different regions. These factors lead to uncertainties and systematic errors in biomass estimations. We developed allometric models to estimate tree AGB in Guyana. These models were based on tree attributes (diameter, height, crown diameter) obtained from terrestrial laser scanning (TLS) point clouds from 72 tropical trees and wood density. We validated our methods and models with data from 26 additional destructively harvested trees. We found that our best TLS-derived allometric models included crown diameter, provided more accurate AGB estimates ( R 2 = 0.92–0.93) than traditional pantropical models ( R 2 = 0.85–0.89), and were especially accurate for large trees (diameter > 70 cm). The assessed pantropical models underestimated AGB by 4 to 13%. Nevertheless, one pantropical model (Chave et al. 2005 without height) consistently performed best among the pantropical models tested ( R 2 = 0.89) and predicted AGB accurately across all size classes—which but for this could not be known without destructive or TLS-derived validation data. Our methods also demonstrate that tree height is difficult to measure in situ, and the inclusion of height in allometric models consistently worsened AGB estimates. We determined that TLS-derived AGB estimates were unbiased. Our approach advances methods to be able to develop, test, and choose allometric models without the need to harvest trees.

scholarly journals CLASSIFICATION OF MOBILE TERRESTRIAL LIDAR POINT CLOUD IN URBAN AREA USING LOCAL DESCRIPTORS

2019 ◽  
Vol XLII-4/W18 ◽  
pp. 1117-1122 ◽  
Author(s):  
M. Zaboli ◽  
H. Rastiveis ◽  
A. Shams ◽  
B. Hosseiny ◽  
W. A. Sarasua
Keyword(s):  
Urban Area ◽  
Point Cloud ◽  
Laser Scanning ◽  
Three Dimensional ◽  
Point Clouds ◽  
Automated Analysis ◽  
Support Vector ◽  
Terrestrial Lidar ◽  
Local Descriptors ◽  
3D Point Clouds

Abstract. Automated analysis of three-dimensional (3D) point clouds has become a boon in Photogrammetry, Remote Sensing, Computer Vision, and Robotics. The aim of this paper is to compare classifying algorithms tested on an urban area point cloud acquired by a Mobile Terrestrial Laser Scanning (MTLS) system. The algorithms were tested based on local geometrical and radiometric descriptors. In this study, local descriptors such as linearity, planarity, intensity, etc. are initially extracted for each point by observing their neighbor points. These features are then imported to a classification algorithm to automatically label each point. Here, five powerful classification algorithms including k-Nearest Neighbors (k-NN), Gaussian Naive Bayes (GNB), Support Vector Machine (SVM), Multilayer Perceptron (MLP) Neural Network, and Random Forest (RF) are tested. Eight semantic classes are considered for each method in an equal condition. The best overall accuracy of 90% was achieved with the RF algorithm. The results proved the reliability of the applied descriptors and RF classifier for MTLS point cloud classification.

scholarly journals Analysis of glacial and periglacial processes using structure from motion

2015 ◽  
Vol 3 (4) ◽  
pp. 1345-1398 ◽  
Author(s):  
L. Piermattei ◽  
L. Carturan ◽  
F. de Blasi ◽  
P. Tarolli ◽  
G. Dalla Fontana ◽  
...  
Keyword(s):  
Structure From Motion ◽  
Laser Scanning ◽  
Surface Displacement ◽  
Surface Characteristics ◽  
Point Clouds ◽  
Rock Glacier ◽  
Dense Image ◽  
Survey Technique ◽  
Close Range ◽  
Geodetic Mass Balance

Abstract. Close-range photo-based surface reconstruction from the ground is rapidly emerging as an alternative to lidar (light detection and ranging), which today represents the main survey technique in many fields of geoscience. The recent evolution of photogrammetry, incorporating computer vision algorithms such as Structure from Motion (SfM) and dense image matching such as Multi-View Stereo (MVS), allows the reconstruction of dense 3-D point clouds for the photographed object from a sequence of overlapping images taken with a digital consumer camera. The objective of our work was to test the accuracy of the ground-based SfM-MVS approach in calculating the geodetic mass balance of a 2.1 km2 glacier in the Ortles-Cevedale Group, Eastern Italian Alps. In addition, we investigated the feasibility of using the image-based approach for the detection of the surface displacement rate of a neighbouring active rock glacier. Airborne laser scanning (ALS) data were used as benchmarks to estimate the accuracy of the photogrammetric DTMs and the reliability of the method in this specific application. The glacial and periglacial analyses were performed using both range and image-based surveying techniques, and the results were then compared. The results were encouraging because the SfM-MVS approach enables the reconstruction of high-quality DTMs which provided estimates of glacial and periglacial processes similar to those achievable by ALS. Different resolutions and accuracies were obtained for the glacier and the rock glacier, given the different survey geometries, surface characteristics and areal extents. The analysis of the SfM-MVS DTM quality allowed us to highlight the limitations of the adopted expeditious method in the studied alpine terrain and the potential of this method in the multitemporal study of glacial and periglacial areas.

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