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A methodological intercomparison of topographic survey techniques for characterizing wadeable streams and rivers
Abstract and Figures
Fine-scale (submeter) resolution digital elevation models (DEMs) created from high precision (subcentimeter) instruments (e.g., total station, rtkGPS, and laser scanning) have become ubiquitous in the field of fluvial geomorphology. They permit a diverse range of spatially explicit analyses including hydraulic modeling, habitat modeling, and geomorphic change detection. While previous studies have assessed the quality of specific topographic survey methods at individual sites or across a limited number of sites, an intercomparison of survey technologies across a diverse range of wadeable streams could help clarify which techniques are feasible, as well as which work best under what circumstances and for what purposes. Although a wealth of existing studies and protocols explain how to undertake each individual technique, in this study we seek to provide guidance on what techniques to use in which circumstances. We quantified the relative quality and the amount of effort spent collecting data to derive bare earth topography from an array of ground-based and airborne survey techniques. We used topographic survey data collected over the summer of 2010 from six sample reaches of varying complexity in the Lemhi River basin, Idaho, USA. We attempted to conduct complete, replicate surveys at each site using total station (TS), real-time kinematic (rtk) GPS, discrete return terrestrial laser scanner (TLS), and airborne LiDaR surveys (ALS). We evaluated the precision and accuracy of derived bare earth DEMs relative to the higher precision total station point data. Discrepancies between pairwise techniques were calculated using propagated DEM errors thresholded at a 95% confidence interval. Mean discrepancies between total station and rtkGPS DEMs were relatively low (≤ 0.05 m), yet TS data collection time was up to 2.4 times longer than rtkGPS. The ALS DEMs had lower accuracy than TS or rtkGPS DEMs, but the aerial coverage and floodplain context of the ALS data set was superior to all other techniques. The TLS bare earth DEM accuracy and precision were lower than any other technique because of vegetation returns misinterpreted as ground returns. Our results are helpful for understanding the strengths and weaknesses of different approaches.
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... Both methods can be used separately or in combination. Using TS and DGNSS methods, in each hour of measurement, hundreds to thousands of high-accuracy points can be acquired (Bangen et al., 2014). ...
... However, RTS can increase productivity, but providing high accuracy digital elevation models of large areas using physical surveying is very expensive and extremely time-consuming. Additionally, since in terrestrial surveying, each point of interest is determined by the surveyor, survey design is influenced by subjectivity (Bangen et al., 2014). The following figure shows a digital contour model and terrestrial instruments (TLS, TS, and GNSS). ...
... Unlike TS technique, GNSS surveying is not limited by constraints such as line of sight. When the sky view is clear and uninterrupted, DGNSS surveying can provide thousands of points per hour of measurement; and DEM can be created by interpolation of survey data (Bangen et al., 2014;Carrivick et al., 2016). ...
Highly detailed topographic mapping at minimal cost and effort has always been one of the developing areas of scientific interest. Image-based remote sensing solutions using Unmanned Aerial Systems (UAS) and Structure from Motion (SfM) with MultiView Stereo (MVS) photogrammetry are the latest automation and advancement in surveying engineering. The aim of this research was to evaluate the accuracy of UAS SfM-MVS as a rapid and low-cost alternative to conventional survey methods. For this purpose, two flights at 100 and 170 m heights Above Ground Level (AGL) for nadir and one flight at 16 m AGL for oblique image acquisition were conducted using fixed-wing and rotary-wing UAS equipped with non-metric cameras. For validating the UAS-SfM products, field measurements were performed using Real-Time Kinematic Global Navigation Satellite System (RTK GNSS), terrestrial laser scanner, and total station. The collected images were processed using three SfM software packages. By applying the SfM-MVS workflow, 22 photogrammetric projects were processed, and as a result, point clouds, triangulated 3D models, Digital Surface Models (DSMs), Digital Terrain Models (DTMs), and orthomosaics were generated. Finally, absolute and relative accuracy assessments were performed. The spatial resolution of orthomosaics and DSMs derived from the UAS images of 16, 100, and 170 m AGL, was 0.005, 0.025, and 0.04 m, respectively. The highest accuracy was obtained from the results derived from 16 m AGL oblique images, which the horizontal and vertical RMSE values were 0.025 and 0.02 m, respectively. From the nadir images of 100 and 170 m AGL, RMSEXY of 0.03 m and RMSEZ of 0.04 and 0.06 m were achieved, respectively. The achieved accuracies of orthomosaics and DSMs reconstructed from 16, and 100 m AGL images are sufficient for most applications requiring terrain analysis, including civil engineering projects.
Keywords: UAS Photogrammetry, Structure from motion (SfM), Digital elevation model, UAV, Terrestrial laser scanning
... Land-based techniques include total station, terrestrial scanning, and a global navigation satellite system (GNSS). However, since this method involves manual measurements, the surveyor's abilities play a significant role on the observation accuracy [7]. According to [8], total stations and GNSSreal-time kinematical (RTK) provide the most accurate bathymetry data for shallow slow-moving water bodies. ...
... According to [8], total stations and GNSSreal-time kinematical (RTK) provide the most accurate bathymetry data for shallow slow-moving water bodies. On the other hand, considering deep streams or reservoirs, GNSS-equipped vessel-mounted surveying techniques (e.g., echo sounders) are more convenient and provide higher precision and accuracy [7,9]. Lastly, field surveys are most suitable for small reaches and are not commonly recommended for an entire stream network due to the logistics, intense labor, high cost, and safety risks [10,11]. ...
Flooding represents a source of hazards for both developed and developing countries. Such events have been causing serious socioeconomic and environmental damage worldwide. Therefore, studies that characterize the features of river channels are essential for flood modeling. In this work, we performed topobathymetric surveys along stretches of three rivers in the São Paulo Metropolitan Region, Brazil. Bathymetric sample points were collected every 50 m, and cross-section surveys were performed every 200 m. In general, the topobathymetric digital elevation model (TBDEM) presents satisfactory results. Lastly, the product generated in this work will be merged into a digital terrain model (DTM) with a spatial resolution of 0.5 m, which in turn, will be made available for future urban flood modeling experiments in the study area.
... Frontiers in Forests and Global Change for 10% or less; moreover, certain images were redundant. Therefore, the number of images required to reconstruct the 3D point-cloud model of the sample plot could not be determined and the production rate of the point cloud could not be guaranteed (Bangen et al., 2014). This finding indicates that a sufficient number of images must be captured during shooting. ...
Introduction
Rubber trees are an important cash crop in Hainan Province; thus, monitoring sample plots of these trees provides important data for determining growth conditions. However, existing monitoring technology and rubber forest sample plot analysis methods are relatively simple and present widespread issues, such as limited monitoring equipment, transportation difficulties, and relatively poor three-dimensional visualization effects in complex environments. These limitations have complicated the development of rubber forest sample plot monitoring.
Method
This study developed a terrestrial photogrammetry system combined with 3D point-cloud reconstruction technology based on the structure from motion with multi-view stereo method and sample plot survey data. Deviation analyses and accuracy evaluations of sample plot information were performed in the study area for trees to explore the practical significance of this method for monitoring rubber forest sample plots. Furthermore, the relationship between the height of the first branch, diameter at breast height (DBH), and rubber tree volume was explored, and a rubber tree standard volume model was established.
Results
The Bias, relative Bias, RMSE, and RRMSE of the height of the first branch measured by this method were −0.018 m, −0.371%, 0.562 m, and 11.573%, respectively. The Bias, relative Bias, RMSE, and RRMSE of DBH were −0.484 cm, −1.943%, −2.454 cm, and 9.859%, respectively, which proved that the method had high monitoring accuracy and met the monitoring requirements of rubber forest sample plots. The fitting results of rubber tree standard volume model had an R ² value of 0.541, and the estimated values of each parameter were 1.745, 0.115, and 0.714. The standard volume model accurately estimated the volume of rubber trees and forests using the first branch height and DBH.
Discussion
This study proposed an innovative planning scheme for a terrestrial photogrammetry system for 3D visual monitoring of rubber tree forests, thus providing a novel solution to issues observed in current sample plot monitoring practices. In the future, the application of terrestrial photogrammetry systems to monitor other types of forests will be explored.
... Although SfM shares many steps with traditional photogrammetry, it is able to retrieve automatically camera positions and orientation as well as scene geometry without knowing that a priori. This advantage makes the SfM way more flexible and cheaper than other digital survey methods, while providing outstanding point densities (Bangen et al. 2014;Smith et al. 2016). Therefore, SfM is commonly exploited in geomorphology to carry out high-resolution DEMs, which is the result of a gridded 3D point cloud produced in the final stages of the SfM-MVS workflow (Micheletti et al. 2015). ...
Chile is frequently affected by different natural hazards that are constantly reshaping the landscape. Particularly, Large and Infrequent Disturbances (LIDs) such as wildfires and volcanic eruptions are capable of affecting entire river catchments by altering the hydrological cycle, reducing the land cover, and boosting sediment remobilization. Given the multitude of effects caused by such disturbances, the response of the catchments is not easily predictable, and different geomorphic responses are expected. The assessment of sediment connectivity can help to better comprehend the overall effects of wildfires and volcanic eruptions on the sediment transfer dynamics at the catchment scale. Sediment connectivity infers the potential transfer of sediment between compartments of the catchment according to the spatial configurations and the processes of such compartments. After a LID, awareness of the degree of linkage between sediment sources and downstream areas is pivotal to reduce the risk and hazard, improving catchment management. In Chile, analysis of sediment connectivity is extremely valuable even tough the availability of high-resolution topographic data and catchments’ accessibility are not always guaranteed. For this reason, much effort should be employed to adapt approaches, based on high-resolution data, to this context by exploiting freely available global data and satellite images and to find trade-offs between data requirements and reliability of the outcomes.KeywordsLarge infrequent disturbancesSediment connectivityMulti-temporal mappingTransferable workflow
... These point-based survey methods provide excellent accuracy, but they can be costly and time-consuming for large areas. 1,16 In addition, the subjective nature of survey design in terrestrial surveying can lead to potential biases. ...
Photogrammetric surveying using unmanned aerial systems (UAS) and structure from motion (SfM) is a rapidly emerging technique that has been widely used as a valuable research tool in geodesy and related disciplines. We studied surveying and three-dimensional (3D) modeling based on UAS and SfM. In particular, we focus on the accuracy and quality of UAS-SfM in 3D modeling and volumetric calculation of a building with an overhanging feature. For this purpose, two aerial surveys were performed using a fixed-wing and a multirotor aircraft with nadir and oblique camera axes. For validating the results, field surveys were carried out using terrestrial laser scanner (TLS), differential global navigation satellite system, and total station. To study the performance of SfM software on the accuracy and quality of point clouds, UAS images were processed using three software packages: Agisoft PhotoScan, Pix4Dmapper, and 3Dsurvey. As a result of photogrammetric image processing, 3D dense point clouds, mesh models, and digital surface models were generated. For validating the UAS-SfM results, the models were compared with the TLS model and field measurements; absolute accuracy assessments and model versus model comparisons were performed. The most accurate and high-quality 3D models comparable to TLS models were obtained from oblique images. PhotoScan generated relatively more accurate 3D models with the horizontal and vertical accuracy of root mean square error 0.025 and 0.02 m, respectively. The maximum discrepancies in dimensions and volume measurements from the UAS-SfM-derived point cloud were at the level of 0.01 m and 0.66 m3 (0.03%). The results highlighted that using a low-cost UAS and SfM photogrammetry, high-accuracy and high-quality 3D models can be generated. The results confirm that with respect to its rapid data acquisition and centimeter-level accuracy, UAS-SfM can be considered as a suitable alternative approach to conventional measurement techniques, especially in engineering and emergency response.
... ALS-derived data are characterized by much higher resolution than satellite data (up to several pt/m 2 ) [28][29][30][31]. The highresolution digital elevation models (DEMs) developed from them provide a good base for differential comparative analyses (DEM of Difference), which results in quantitative estimates of geomorphic changes [32][33][34]. However, ALS has significant limitations, which are mainly related to the high cost of the flight. ...
A four-day glacier-melt flood (13–16 August 2013) caused abrupt geomorphic changes in the proglacial gravel-bed Scott River, which drains the small (10 km2) Scott Glacier catchment (SW Svalbard). This type of flood occurs on Svalbard increasingly during periods of abnormally warm or rainy weather in summer or early autumn, and the probability of occurrence grows in direct proportion to the increase in temperature and/or precipitation intensity. In the summer of 2013, during the measurement season, the highest daily precipitation (17 mm) occurred on 13 August. During the following four days, it constituted in total 47 mm, i.e., 50% of the precipitation total for the measurement period of 2013. The largest flood in 20 years was caused by high precipitation with a synchronous rise in temperature from about 1.0 to 8.6 °C. These values exceeded multi-year averages (32 mm and 5.0 °C, respectively) at an average discharge of 0.9 m3/s (melt season mean 1986–2011). These conditions caused a rapid and abrupt response of the river with the dominant (90%) glacier-fed. The increase in discharge to 4.6 m3/s, initiated by the glacial flood, mobilized significant amounts of sediment in the river bed and channel. Geomorphic changes within the alluvial fan as an area of 58,940 m2, located at the mouth of the Scott River, were detected by multi-sites terrestrial laser scanning using a Leica Scan Station C10 and then estimated using Geomorphic Change Detection (GCD) software. The changes found involved 39% of the alluvial fan area (23,231 m2). The flood-induced total area of lowering (erosion) covered 26% of the alluvial fan (6035 m2), resulting in the removal of 1183 ± 121 m3 of sediment volume. During the final phase of the flood, two times more sediment (1919 ± 344 m3) was re-deposited within the alluvial fan surface, causing significant aggradation on 74% of its area (17,196 m2). These geomorphic changes resulted in an average lowering (erosion) of the alluvial fan surface of 0.2 m and an average rising (deposition) of 0.1 m.
... Real time global positioning systems and total station approach provide precise bathymetry data for the shallow river (Hilldale and Raff, 2008). Because these methods require manual measurements, the skill of the surveyor has a substantial impact on the measurement accuracy (Bangen et al., 2014). The security concerns of the surveyor, particularly in rapidly-flowing or deeper rivers, impede the application of these survey techniques. ...
Unoccupied aerial vehicles (UAVs) with passive optical sensors have become popular for reconstructing topography using Structure from Motion (SfM) photogrammetry. Advances in UAV payloads and the advent of solid‐state LiDAR have enabled consumer‐grade active remote sensing equipment to become more widely available, potentially providing opportunities to overcome some challenges associated with SfM photogrammetry, such as vegetation penetration and shadowing, that can occur when processing UAV‐acquired images. We evaluate the application of a DJI Zenmuse L1 solid‐state LiDAR sensor on a Matrice 300 RTK UAV to generate digital elevation models (DEMs). To assess flying height (60–80 m) and speed parameters (5–10 ms ⁻¹ ) on accuracy, four point clouds were acquired at a test site. These point clouds were used to develop a processing workflow to georeference, filter and classify the point clouds to produce a raster DEM product. A dense control network showed that there was no significant difference in georeferencing from differing flying height or speed. Building on the test results, a 3 km reach of the River Feshie was surveyed, collecting over 755 million UAV LiDAR points. The Multiscale Curvature Classification algorithm was found to be the most suitable classifier of ground topography. GNSS check points showed a mean vertical residual of −0.015 m on unvegetated gravel bars. Multiscale Model to Model Cloud Comparison (M3C2) residuals compared UAV LiDAR and Terrestrial Laser Scanner point clouds for seven sample sites demonstrating a close match with marginally zero residuals. Solid‐state LiDAR was effective at penetrating sparse canopy‐type vegetation but was less penetrable through dense ground‐hugging vegetation (e.g. heather, thick grass). Whilst UAV solid‐state LiDAR needs to be supplemented with bathymetric mapping to produce wet–dry DEMs, by itself, it offers advantages to comparable geomatics technologies for kilometre‐scale surveys. Ten best practice recommendations will assist users of UAV solid‐state LiDAR to produce bare earth DEMs.
Digital elevation models (DEMs) derived from ground-based topographic surveys have become ubiquitous in the field of fluvial geomorphology. Their wide application in spatially explicit analysis includes hydraulic modeling, habitat modeling, and morphological sediment budgeting. However, there is a lack of understanding regarding the repeatability and precision of DEMs derived from ground-based surveys conducted by different, and inherently subjective, observers. This is of particular concern when we consider the proportion of studies and monitoring programs that are implemented across multiple sites and over time by different observers. We used a case study from the Columbia Habitat Monitoring Program (CHaMP), where seven field crews sampled the same six sites, to quantify the magnitude and effect of observer variability on DEMs interpolated from total station surveys. We quantified the degree to which DEM-derived metrics and measured geomorphic change were repeatable. Across all six sites, we found an average elevation standard deviation of 0.05 m among surveys, and a mean total range of 0.16 m. A variance partition between site, crew, and unexplained errors for several topographically derived metrics showed that crew variability never accounted for > 1.5% of the total variability. We calculated minor geomorphic changes at one site following a relatively dry flow year between 2012 and 2011. Calculated changes were minimal (unthresholded net changes ± 1-3 cm) with six crews detecting an indeterminate sediment budget and one crew detecting a minor net erosional sediment budget. While crew variability does influence the quality of topographic surveys, this study highlights that when consistent surveying methods are employed, the data sets are still sufficient to support derivation of topographic metrics and conduct basic geomorphic change detection. This article is protected by copyright. All rights reserved.
Recent advances in technology have revolutionized the acquisition of
topographic data, offering new perspectives on the structure and
morphology of the Earth's surface. These developments have had a
profound impact on the practice of river science, creating a step change
in the dimensionality, resolution, and precision of fluvial terrain
models. The emergence of "hyperscale" survey methods, including
structure from motion photogrammetry and terrestrial laser scanning
(TLS), now presents the opportunity to acquire 3-D point cloud data that
capture grain-scale detail over reach-scale extents. Translating these
data into geomorphologically relevant products is, however, not
straightforward. Unlike traditional survey methods, TLS acquires
observations rapidly and automatically, but unselectively. This results
in considerable "noise" associated with backscatter from vegetation and
other artifacts. Moreover, the large data volumes are difficult to
visualize; require very high capacity storage; and are not incorporated
readily into GIS and simulation models. In this paper we analyze the
geomorphological integrity of multiscale terrain models rendered from a
TLS survey of the braided River Feshie, Scotland. These raster terrain
models are generated using a new, computationally efficient geospatial
toolkit: the topographic point cloud analysis toolkit (ToPCAT). This
performs an intelligent decimation of point cloud data into a set of
2.5-D terrain models that retain information on the high-frequency
subgrid topography, as the moments of the locally detrended elevation
distribution. The results quantify the degree of terrain generalization
inherent in conventional fluvial DEMs and illustrate how subgrid
topographic statistics can be used to map the spatial pattern of
particle size, grain roughness, and sedimentary facies at the reach
scale.
From basic theory to practical application this book provides an introduction to the concepts needed to understand and use GPS. It is written in a way to cover GPS techniques in everyday practice. The seven chapters in this user friendly manual are as follows: the GPS signal; biases and solutions; the framework of GPS; receivers and methods; coordinates; planning a survey; observing; and postmission processing. Each chapter has its own reference list for further reading and research.
The potential for mapping in-channel morphology within shallow gravel-bed rivers using airborne multispectral imagery and aerial photography is illustrated using a case study from the River Tummel, Scotland. The technique described relies on a good correlation between observed light reflectance levels from a water body and water depth. Measured water depths are regressed against reflectance levels derived from airborne multispectral imagery and black-and-white aerial photographs, to obtain equations that can be used for mapping channel bathymetry. The technique has a great deal of potential for wideranging applications, including detailed morphological surveys, assessing in-channel changes and mapping riverine habitats.
The production of topographic datasets is of increasing interest and application throughout the geomorphic sciences, and river science is no exception. Consequently, a wide range of topographic measurement methods have evolved. Despite the range of available methods, the production of high resolution, high quality digital elevation models (DEMs) requires a significant investment in personnel time, hardware and/or software. However, image-based methods such as digital photogrammetry have been decreasing in costs. Developed for the purpose of rapid, inexpensive and easy three-dimensional surveys of buildings or small objects, the ‘structure from motion’ photogrammetric approach (SfM) is an image-based method which could deliver a methodological leap if transferred to geomorphic applications, requires little training and is extremely inexpensive. Using an online SfM program, we created high-resolution digital elevation models of a river environment from ordinary photographs produced from a workflow that takes advantage of free and open source software. This process reconstructs real world scenes from SfM algorithms based on the derived positions of the photographs in three-dimensional space. The basic product of the SfM process is a point cloud of identifiable features present in the input photographs. This point cloud can be georeferenced from a small number of ground control points collected in the field or from measurements of camera positions at the time of image acquisition. The georeferenced point cloud can then be used to create a variety of digital elevation products. We examine the applicability of SfM in the Pedernales River in Texas (USA), where several hundred images taken from a hand-held helikite are used to produce DEMs of the fluvial topographic environment. This test shows that SfM and low-altitude platforms can produce point clouds with point densities comparable with airborne LiDAR, with horizontal and vertical precision in the centimeter range, and with very low capital and labor costs and low expertise levels. Copyright © 2012 John Wiley & Sons, Ltd.
3D surface representation has long been a source of information describing surface character and facilitating an understanding of system dynamics from micro-scale (e.g. sand transport) to macro-scale (e.g. drainage channel network evolution). Data collection has been achieved through field mapping techniques and the use of remotely sensed data. Advances in this latter field have been considerable in recent years with new rapid-acquisition methods being developed centered around laser based technology. The advent of airborne and field based laser scanning instruments has allowed researchers to collect high density accurate data sets and these are revealing a wealth of new information and generating important new ideas concerning terrain characterisation and landform dynamics. The proposed book collates a series of invited peer revieved papers presented at the a conference on geoinformatics and LIDAR to be held at the National Centre for Geocomputation based in the National University of Ireland, Maynooth. Current constraints in field survey and DEM construction are reviewed together with technical and applied issues around the new technology. The utility of the data in process modelling is also covered. The book will be of great value to researchers in the field of geomorphology, geostatistics, remote sensing and GIS and will prove extremely useful to students and practitioners concerned with terrain analysis. The proposed work will: Highlight major technological breakthrough in 3D data collection. Feature examples of application across a wide range of environmental areas. Critically evaluate the role of laser based techniques in the environment. Detail theory and application of laser techniques in the natural environment.