Digital Elevation Modeling of Inaccessible Slope by Using Close-range Photogrammetric Data

Digital Elevation Model (DEM) currently is extensively used extensively in various applications such as for natural hazard assessment and monitoring of high risk areas. DEM data source of inaccessible areas can be collected by using several methods, but mostly are costly and requires sophisticated instruments. Due to these conditions, close-range photogrammetry offers a low cost alternative solution. Materials presented in this thesis are based on the experiments to explain the application of close-range photogrammetry with the aid of commercial digital pocket camera as DEM data collection tools, applied on inaccessible slope areas. The analysis covers calibration of the camera and surveying instruments, DEM data collections, data processing and visualization, together with DEM quality measures. The data collections are accomplished on several study areas with different topographical characteristics by using close-range photogrammetry technique. The sampling points were selected on stereo model, by using three types of sampling methods. The DEM quality measures are assessed by following elevation interpolation error and volumetric difference error analyses. The representation of the DEM is generated using TIN-based (Triangular Irregular Network) approach. The result shows that the method is able to be applied for three dimensional (3D) modeling of potentially unstable slope areas, with accuracy of less than 15 cm in RMS for elevation error and is less than 1% in volume error. The result has indicated that topographical condition has not affected the accuracy of generated DEM. Improvement of point density radically enhances the DEM’s quality, up to a certain level of point density beyond which the increment of the accuracy is not significant. The difference setting of focal length has also influences the quality of captured images, and drastically affects the accuracy of the DEM. If the accuracy of the DEM is a matter of concern, the preferred sampling method is selective sampling, while if accuracy and DEM’s time generation are the concern the most effective sampling method is regular sampling method. Since there was no permanent points on the observed slope surface, velocity and direction of landslide could not be accurately determined. However the distribution of massmovement and elevation changed on the slope surfaces can be modeled through spatialcalculation of overlaying DEMs together with profiling of cross-section and longitudinalsection of the generated DEMs

Digital Elevation Modeling oflnaccessible Slope by Using Close-range Photogrammetric Data

Digital Elevation Model (DEM) currently is extensively used extensively in vanous applications such as for natural hazard assessment and monitoring of high risk areas. DEM data source of inaccessible areas can be collected by using several methods, but mostly are costly and requires sophisticated instruments. Due to these conditions, close-range photograrnmetry offers a low cost alternative solution. Materials presented in this thesis are based on the experiments to explain the application of close-range photogrammetry with the aid of commercial digital pocket camera as DEM data collection tools, applied on inaccessible slope areas. The analysis covers calibration of the camera and surveying instruments, DEM data collections, data processing and visualization, together with DEM quality measures. The data collections are accomplished on several study areas with different topographical characteristics by using close-range photograrnmetry technique. The sampling points were selected on stereo model, by using three types of sampling methods. The DEM quality measures are assessed by following elevation interpolation error and volumetric difference error analyses. The representation of the DEM is generated using TIN-based (Triangular Irregular Network) approach. The result shows that the method is able to be applied for three dimensional (3D) modeling of potentially unstable slope areas, with accuracy of less than 15 em in RMS for elevation error and is less than 1% in volume error. The result has indicated that topographical condition has not affected the accuracy of generated DEM. Improvement of point density radically enhances the DEM's quality, up to a certain level of point density beyond which the increment of the accuracy is not significant. The difference setting of focal length has also influences the quality of captured images, and drastically affects the accuracy of the DEM. If the accuracy of the DEM is a matter of concern, the preferred sampling method is selective sampling, while if accuracy and DEM's time generation are the concern the most effective sampling method is regular sampling method. Since there was no permanent points on the observed slope surface, velocity and direction of landslide could not be accurately determined. However the distribution of massmovement and elevation changed on the slope surfaces can be modeled through spatialcalculation of overlaying DEMs together with profiling of cross-section and longitudinalsection of the generated DEMs

DEM investigation of the influence of particulate properties and operating conditions on the mixing process in rotary drums: Part 1-Determination of the DEM parameters and calibration process

This paper's goal was to select methods and a calibration procedure which would lead to the determination of relevant parameters of a discrete element method (DEM) and virtual material creation. Seven particulates were selected with respect to their shape (spherical and non-spherical), size and density. The first calibration experiment involved "packing test" to determine the shape accuracy and bulk density of virtual packed particulates. The series of simulations were compared with real experiments, and the size, shape and density of virtual particles were optimized. Using three apparatuses, the input parameter values were experimentally determined for a contact model that defines the behavior of particulates in DEM simulations. The research part of the paper examines the influence of factors such as particle number; pile formation method; and the method of evaluation of the angle of repose on the process of the calibration of virtual material. The most reproducible results were achieved by the "pilling" method and by the rotating drum-both evaluated by the geometric method. However, it is always advisable to make an overall visual comparison of the slope shape between the calibration simulation and the experimental curves. The bowl's diameter to particle size ratio should be greater than 25, and the calibration experiment should contain approximately 4000 particles to ensure representative results during angle of repose calibration experiment.Web of Science82art. no. 22

Photogrammetric techniques for across-scale soil erosion assessment: Developing methods to integrate multi-temporal high resolution topography data at field plots

Soil erosion is a complex geomorphological process with varying influences of different impacts at different spatio-temporal scales. To date, measurement of soil erosion is predominantly realisable at specific scales, thereby detecting separate processes, e.g. interrill erosion contrary to rill erosion. It is difficult to survey soil surface changes at larger areal coverage such as field scale with high spatial resolution. Either net changes at the system outlet or remaining traces after the erosional event are usually measured. Thus, either quasi-point measurements are extrapolated to the corresponding area without knowing the actual sediment source as well as sediment storage behaviour on the plot or erosion rates are estimated disrupting the area of investigation during the data acquisition impeding multi-temporal assessment. Furthermore, established methods of soil erosion detection and quantification are typically only reliable for large event magnitudes, very labour and time intense, or inflexible. To better observe soil erosion processes at field scale and under natural conditions, the development of a method is necessary, which identifies and quantifies sediment sources and sinks at the hillslope with high spatial resolution and captures single precipitation events as well as allows for longer observation periods. Therefore, an approach is introduced, which measures soil surface changes for multi-spatio-temporal scales without disturbing the area of interest. Recent advances regarding techniques to capture high resolution topography (HiRT) data led to several promising tools for soil erosion measurement with corresponding advantages but also disadvantages. The necessity exists to evaluate those methods because they have been rarely utilised in soil surface studies. On the one hand, there is terrestrial laser scanning (TLS), which comprises high error reliability and retrieves 3D information directly. And on the other hand, there is unmanned aerial vehicle (UAV) technology in combination with structure from motion (SfM) algorithms resulting in UAV photogrammetry, which is very flexible in the field and depicts a beneficial perspective. Evaluation of the TLS feasibility reveals that this method implies a systematic error that is distance-related and temporal constant for the investigated device and can be corrected transferring calibration values retrieved from an estimated lookup table. However, TLS still reaches its application limits quickly due to an unfavourable (almost horizontal) scanning view at the soil surface resulting in a fast decrease of point density and increase of noise with increasing distance from the device. UAV photogrammetry allows for a better perspective (birds-eye view) onto the area of interest, but possesses more complex error behaviour, especially in regard to the systematic error of a DEM dome, which depends on the method for 3D reconstruction from 2D images (i.e. options for additional implementation of observations) and on the image network configuration (i.e. parallel-axes and control point configuration). Therefore, a procedure is developed that enables flexible usage of different cameras and software tools without the need of additional information or specific camera orientations and yet avoiding this dome error. Furthermore, the accuracy potential of UAV photogrammetry describing rough soil surfaces is assessed because so far corresponding data is missing. Both HiRT methods are used for multi-temporal measurement of soil erosion processes resulting in surface changes of low magnitudes, i.e. rill and especially interrill erosion. Thus, a reference with high accuracy and stability is a requirement. A local reference system with sub-cm and at its best 1 mm accuracy is setup and confirmed by control surveys. TLS and UAV photogrammetry data registration with these targets ensures that errors due to referencing are of minimal impact. Analysis of the multi-temporal performance of both HiRT methods affirms TLS to be suitable for the detection of erosion forms of larger magnitudes because of a level of detection (LoD) of 1.5 cm. UAV photogrammetry enables the quantification of even lower magnitude changes (LoD of 1 cm) and a reliable observation of the change of surface roughness, which is important for runoff processes, at field plots due to high spatial resolution (1 cm²). Synergetic data fusion as a subsequent post-processing step is necessary to exploit the advantages of both HiRT methods and potentially further increase the LoD. The unprecedented high level of information entails the need for automatic geomorphic feature extraction due to the large amount of novel content. Therefore, a method is developed, which allows for accurate rill extraction and rill parameter calculation with high resolution enabling new perspectives onto rill erosion that has not been possible before due to labour and area access limits. Erosion volume and cross sections are calculated for each rill revealing a dominant rill deepening. Furthermore, rill shifting in dependence of the rill orientation towards the dominant wind direction is revealed. Two field plots are installed at erosion prone positions in the Mediterranean (1,000 m²) and in the European loess belt (600 m²) to ensure the detection of surface changes, permitting the evaluation of the feasibility, potential and limits of TLS and UAV photogrammetry in soil erosion studies. Observations are made regarding sediment connectivity at the hillslope scale. Both HiRT methods enable the identification of local sediment sources and sinks, but still exhibiting some degree of uncertainty due to the comparable high LoD in regard to laminar accumulation and interrill erosion processes. At both field sites wheel tracks and erosion rills increase hydrological and sedimentological connectivity. However, at the Mediterranean field plot especially dis-connectivity is obvious. At the European loess belt case study a triggering event could be captured, which led to high erosion rates due to high soil moisture contents and yet further erosion increase due to rill amplification after rill incision. Estimated soil erosion rates range between 2.6 tha-1 and 121.5 tha-1 for single precipitation events and illustrate a large variability due to very different site specifications, although both case studies are located in fragile landscapes. However, the susceptibility to soil erosion has different primary causes, i.e. torrential precipitation at the Mediterranean site and high soil erodibility at the European loess belt site. The future capability of the HiRT methods is their potential to be applicable at yet larger scales. Hence, investigations of the importance of gullys for sediment connectivity between hillslopes and channels are possible as well as the possible explanation of different erosion rates observed at hillslope and at catchment scales because local sediment sink and sources can be quantified. In addition, HiRT data can be a great tool for calibrating, validating and enhancing soil erosion models due to the unprecedented level of detail and the flexible multi-spatio-temporal application

Shape from Shading法を用いた天体表面の斜面推定に関する研究

学位の種別: 修士University of Tokyo(東京大学

A fractal fragmentation model for rockfalls

The final publication is available at Springer via http://dx.doi.org/10.1007/s10346-016-0773-8The impact-induced rock mass fragmentation in a rockfall is analyzed by comparing the in situ block size distribution (IBSD) of the rock mass detached from the cliff face and the resultant rockfall block size distribution (RBSD) of the rockfall fragments on the slope. The analysis of several inventoried rockfall events suggests that the volumes of the rockfall fragments can be characterized by a power law distribution. We propose the application of a three-parameter rockfall fractal fragmentation model (RFFM) for the transformation of the IBSD into the RBSD. A discrete fracture network model is used to simulate the discontinuity pattern of the detached rock mass and to generate the IBSD. Each block of the IBSD of the detached rock mass is an initiator. A survival rate is included to express the proportion of the unbroken blocks after the impact on the ground surface. The model was calibrated using the volume distribution of a rockfall event in Vilanova de Banat in the Cadí Sierra, Eastern Pyrenees, Spain. The RBSD was obtained directly in the field, by measuring the rock block fragments deposited on the slope. The IBSD and the RBSD were fitted by exponential and power law functions, respectively. The results show that the proposed fractal model can successfully generate the RBSD from the IBSD and indicate the model parameter values for the case study.Peer ReviewedPostprint (author's final draft

Flow-generated displacement of reinforced granular slopes using the discrete element method

2017 Fall.Includes bibliographical references.The Discrete Element Method (DEM) has been used by researchers to study the behavior of granular material. It is based on the discrete nature of the granular media and tracks the displacements of individual particles and their interactions at every time-step of the simulation. This approach was used in this study to investigate the flow-generated displacement of spring-reinforced planar granular slopes. A Discrete Element (DE) code was created using MATLAB and FORTRAN to carry out the simulations. The code was validated by comparison of simulation results with analytical solutions. Granular slopes with particle radii ranging from 5 to 10 mm and various initial slopes were generated. Reinforced slopes were created by adding reinforcement, in the form of linear springs restraining surface particles, to the original geometry. The surface of both the original and the reinforced slopes was exposed to flow-generated drag forces. Various reinforcement patterns were modeled and the resulting flow-generated displacements were measured and studied. It was found that slope reinforcing can either delay or prevent flow-generated movements and the effectiveness of the reinforcing depends on the slope of the packing, size of the drag force and the pattern of the reinforcing