https://pure.aber.ac.uk/portal/files/4916016/Westoby_et_al._GEOMORPH_2012_Accepted.pdf

‘Structure-from-Motion’ photogrammetry: A low-cost, effective tool for geoscience applications

Topographic measurements for detailed studies of processes such as erosion or mass movement are usually acquired by expensive laser scanners or rigorous photogrammetry. Here, we test and use an alternative technique based on freely available computer vision software which allows general geoscientists to easily create accurate 3D models from field photographs taken with a consumer-grade camera. The approach integrates structure-from-motion (SfM) and multi-view-stereo (MVS) algorithms and, in contrast to traditional photogrammetry techniques, it requires little expertise and few control measurements, and processing is automated. To assess the precision of the results, we compare SfM-MVS models spanning spatial scales of centimeters (a hand sample) to kilometers (the summit craters of Piton de la Fournaise volcano) with data acquired from laser scanning and formal close-range photogrammetry. The relative precision ratio achieved by SfM-MVS (measurement precision : observation distance) is limited by the straightforward camera calibration model used in the software, but generally exceeds 1:1000 (i.e. centimeter-level precision over measurement distances of 10s of meters). We apply SfM-MVS at an intermediate scale, to determine erosion rates along a ~50-m-long coastal cliff. Seven surveys carried out over a year indicate an average retreat rate of 0.70±0.05 m a-1. Sequential erosion maps (at ~0.05 m grid resolution) highlight the spatio-temporal variability in the retreat, with semivariogram analysis indicating a correlation between volume loss and length scale. Compared with a laser scanner survey of the same site, SfM-MVS produced comparable data and reduced data collection time by ~80%.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2011JF002289

Straightforward reconstruction of 3D surfaces and topography with a camera: Accuracy and geoscience application

Accurate, precise and rapid acquisition of topographic data is fundamental to many sub-disciplines of physical geography. Technological developments over the past few decades have made fully distributed data sets of centimetric resolution and accuracy commonplace, yet the emergence of Structure from Motion (SfM) with Multi-View Stereo (MVS) in recent years has revolutionised three-dimensional topographic surveys in physical geography by democratising data collection and processing. SfM-MVS originates from the fields of computer vision and photogrammetry, requires minimal expensive equipment or specialist expertise and, under certain conditions, can produce point clouds of comparable quality to existing survey methods (e.g. Terrestrial Laser Scanning). Consequently, applications of SfM-MVS in physical geography have multiplied rapidly. There are many practical options available to physical geographers when planning a SfM-MVS survey (e.g. platforms, cameras, software), yet, many SfM-MVS end-users are uncert...

/pdf/structure-from-motion-photogrammetry-in-physical-geography-1yja1579z5.pdf

Structure from Motion Photogrammetry in Physical Geography

https://meetingorganizer.copernicus.org/EGU2011/EGU2011-8188.pdf

Geomorphometric assessment of spatial sediment connectivity in small Alpine catchments

. Photogrammetry and geosciences have been closely linked since the late 19th century due to the acquisition of high-quality 3-D data sets of the environment, but it has so far been restricted to a limited range of remote sensing specialists because of the considerable cost of metric systems for the acquisition and treatment of airborne imagery. Today, a wide range of commercial and open-source software tools enable the generation of 3-D and 4-D models of complex geomorphological features by geoscientists and other non-experts users. In addition, very recent rapid developments in unmanned aerial vehicle (UAV) technology allow for the flexible generation of high-quality aerial surveying and ortho-photography at a relatively low cost. The increasing computing capabilities during the last decade, together with the development of high-performance digital sensors and the important software innovations developed by computer-based vision and visual perception research fields, have extended the rigorous processing of stereoscopic image data to a 3-D point cloud generation from a series of non-calibrated images. Structure-from-motion (SfM) workflows are based upon algorithms for efficient and automatic orientation of large image sets without further data acquisition information, examples including robust feature detectors like the scale-invariant feature transform for 2-D imagery. Nevertheless, the importance of carrying out well-established fieldwork strategies, using proper camera settings, ground control points and ground truth for understanding the different sources of errors, still needs to be adapted in the common scientific practice. This review intends not only to summarise the current state of the art on using SfM workflows in geomorphometry but also to give an overview of terms and fields of application. Furthermore, this article aims to quantify already achieved accuracies and used scales, using different strategies in order to evaluate possible stagnations of current developments and to identify key future challenges. It is our belief that some lessons learned from former articles, scientific reports and book chapters concerning the identification of common errors or "bad practices" and some other valuable information may help in guiding the future use of SfM photogrammetry in geosciences.

/pdf/image-based-surface-reconstruction-in-geomorphometry-merits-g68ovc3a9x.pdf

Image-based surface reconstruction in geomorphometry - merits, limits and developments

Small‐Format Aerial Photography

*Dirk Rieke-Zapp and Mark A. Nearing, USDA-ARS National Soil Erosion Research Laboratory, 1196 Soil Building, Purdue Univ., West Lafayette, Indiana, 47907-1196 USA; Jean Poesen, Laboratory for Experimental Geomorphology, K.U. Leuven, Belgium; Fund for Scientific Research Flanders. *Corresponding author: zapp@purdue.edu ABSTRACT In recent times more attention in research has been given to the role rock fragments play in soil erosion. The demand to focus on the interaction between fine particles and rock fragments, and their effects on soil loss, has increased because these types of soils are ubiquitous. Therefore, a study with twenty flume experiments was conducted in which concentrated flow was applied to a Miami Silt Loam, a typical soil of the Midwest of the United States. The study focused on four different treatments: slope (7 and 14%), flow discharge (5.7 and 11.4 L min), rock fragment content (0, 5, 10, 20, 40% vol) and flow duration. The results show the development of an erosion pavement with time and a surface armoring for soils containing rock fragments. The intensity and the speed of the development of this pavement are dependent on slope, discharge, and initial rock fragment content as well as flow duration. An increase of the rock fragment cover protecting the eroding surface helps to prevent soil loss. The more rock fragments were incorporated with the soil, the less sediment yield was observed in general. Soil surface roughness was evaluated by means of a laser scanner device and a counting method to find an index for the described armoring effect and to identify the increase of cover during the experiments.

/pdf/rocks-and-rills-the-impact-of-rock-fragments-on-soil-loss-by-2zgg2spdrw.pdf

Rocks and rills: the impact of rock fragments on soil loss by concentrated flow erosion in laboratory experiments

Rockfalls and landslides are major types of natural hazards worldwide that kill or injure a large number of individuals and cause very high costs every year. Risk assessment of such dangerous events requires an accurate evaluation of the geology, hydrogeology, morphology and interrelated factors such as environmental conditions and human activities. It is of particular importance for engineers and geologists to assess slope stability and dynamics in order to take appropriate, effective and timely measures against such events. This paper presents a decision-tool for geo-risk assessment on the basis of a knowledge-based system. The integration of such a tool with novel measurement sensors into an advanced system for geo-risk monitoring, which performs data fusion on-line, is innovative. To enable such a system, a knowledge base capturing domain knowledge formally is developed, which to the best of our knowledge is unprecedented; the completed part for initial risk assessment works quite well, as extensive experiments with a number of human experts have shown.

/pdf/knowledge-based-geo-risk-assessment-for-an-intelligent-4naba1zsxz.pdf

Knowledge-Based Geo-risk Assessment for an Intelligent Measurement System

Summary Photogrammetry is a well established tool in the earth sciences for retrieval of qualitative as well as quantitative information from imagery. In the past, analysis was predominantly performed on publicly available or archival imagery taken by trained photogrammetrists. In this case mission planning, image acquisition, camera calibration, and image orientation were often readily available to earth scientists at the start of their analyses. The photogrammetric products that are of interest to earth scientists are typically digital elevation models (DEMs) or orthophotos that are processed for analysis. Monitoring of changes in the landscape, or tracking the course of a laboratory experiment requires data for different time steps for quantification of processes. Although earth scientists apply well-established photogrammetric techniques for data acquisition, workflow and hardware setup can pose challenges to the users with little experience. Expectations regarding accuracy in object space are often close to the theoretical limit of a given setup and are difficult to meet under field conditions or during short breaks of experiments for data capture. Therefore, the workflow for data acquisition must be streamlined and the hardware optimized to yield optimum accuracy under these conditions. In this paper we will present some geomorphologic experiments where digital photogrammetry was employed for data capture. Special attention was given to uncommon or novel solutions of camera setup and hardware easing data capture or image processing for analysis in the earth sciences. 1 Soil Erosion Experiments in the Laboratory

/pdf/the-application-of-photogrammetry-for-process-quantification-11r1ro2pts.pdf

The Application of Photogrammetry for Process Quantification in Geomorphology - Examples of Modern Applications

With the UK gaining responsibility for Commission V at the Beijing Congress in 2008, there was an opportunity to create a new working group focusing on earth science applications at close range. The earth science community has had a long tradition of using close range photogrammetry, and more recently laser scanning, and such opportunities have not been fully recognised by ISPRS in the past. Formation of a new ISPRS Working Group helps to bridge this gap and promotes the skills of ISPRS members more widely. The purpose of this paper is to justify the creation of Working Group V6 and identify some of the activities conducted over the last four years. In particular, reference will be made to the various technical sessions which have been organised and supported across the world, the first resulting in a Special Issue of The Photogrammetric Record published in September 2010. In addition, Working Group V6 has been responsible for the creation of two freely available guidance documents entitled "tips for the effective use of digital close range photogrammetry and terrestrial laser scanning". The former focuses on close range digital photogrammetry and has developed through several iterations with input from both academic and industrial users from around the world. For this reason it should be of distinct value to new and perhaps non-expert users interested in using photogrammetry for earth science applications. The paper includes a discussion which considers whether the initial four years of activity have been successful. A superficial assessment based upon the number of members attracted worldwide would suggest that this has indeed been the case. A deeper comparison between proposed activities and those actually achieved suggest some discrepancy, which is perhaps inevitable as Working Group Officers clearly have other responsibilities. However, examination of papers published in the earth surface journals reveal high incidence of photogrammetry and laser scanning appearing in recent work. This should encourage members of Working Group V6 in future activities and collaborations.

/pdf/photogrammetry-and-laser-scanning-for-the-earth-44ugm5knvn.pdf

Dirk Rieke-Zapp

Papers

Small‐Format Aerial Photography

Rocks and rills: the impact of rock fragments on soil loss by concentrated flow erosion in laboratory experiments

Knowledge-Based Geo-risk Assessment for an Intelligent Measurement System

The Application of Photogrammetry for Process Quantification in Geomorphology - Examples of Modern Applications

Photogrammetry and laser scanning for the earth sciencesworking group v6