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Emerging technology has immense potential to increase the scale and efficiency of marine conservation. One such technology is large‐area imaging (LAI), which relies on structure‐from‐motion photogrammetry to create composite products, including 3‐dimensional (3‐D) environmental models, that are larger in spatial extent than the individual images used to create them. Use of LAI has become widespread in certain fields of marine science, primarily to measure the 3D structure of benthic ecosystems and track change over time. However, the use of LAI in the field of marine conservation appears limited. We conducted a review of the coral reef literature on the use of LAI to identify research themes and regional trends in applications of this technology. We also surveyed 135 coral reef scientists and conservation practitioners to determine community familiarity with LAI, evaluate barriers practitioners face in using LAI, and identify applications of LAI believed to be most exciting or relevant to coral conservation. Adoption of LAI was limited primarily to researchers at institutions based in advanced economies and was applied infrequently to conservation, although conservation practitioners and survey respondents from emerging economies indicated they expect to use LAI in the future. Our results revealed disconnect between current LAI research topics and conservation priorities identified by practitioners, highlighting the need for more diverse, conservation‐relevant research using LAI. We provide recommendations for how early adopters of LAI (typically Global North scientists from well‐resourced institutions) can facilitate access to this conservation technology. These recommendations include developing training resources, creating partnerships for data storage and analysis, publishing standard operating procedures for LAI workflows, standardizing methods, developing tools for efficient data extraction from LAI products, and conducting conservation‐relevant research using LAI. [ABSTRACT FROM AUTHOR]

USS Emmons is an American Second World War battleship of that sunk off Kouri Island in Okinawa, Japan, as a result of participating in the Battle of Okinawa in 1945. It was attacked by Kamikaze Special Attack Units and became inoperable. A high-quality 3D Structure-from-Motion (SfM) model was created that served to plan diver-based investigations and record the current state of the site. Together with the war-related documents from US and Japan, this research has revealed scientific evidence that has been used to reconstruct the battle of Emmons and the kamikaze planes. [ABSTRACT FROM AUTHOR]

Advances in image-based remote sensing using unmanned aerial vehicles (UAV) and structure-from-motion (SfM) photogrammetry continue to improve our ability to monitor complex landforms over representative spatial and temporal scales. As with other water-worked environments, coastal sediments respond to shaping processes through the formation of multi-scale topographic roughness. Although this topographic complexity can be an important marker of hydrodynamic forces and sediment transport, it is seldom characterized in typical beach surveys due to environmental and technical constraints. In this study, we explore the feasibility of using SfM photogrammetry augmented with an RTK quadcopter for monitoring the coastal topographic complexity at the beach-scale in a macrotidal environment. The method had to respond to resolution and time constraints for a realistic representation of the topo-morphological features from submeter dimensions and survey completion in two hours around low tide to fully cover the intertidal zone. Different tests were performed at two coastal field sites with varied dimensions and morphologies to assess the photogrammetric performance and eventual means for optimization. Our results show that, with precise image positioning, the addition of a single ground control point (GCP) enabled a global precision (RMSE) equivalent to that of traditional GCP-based photogrammetry using numerous and well-distributed GCPs. The optimal model quality that minimized vertical bias and random errors was achieved from 5 GCPs, with a two-fold reduction in RMSE. The image resolution for tie point detection was found to be an important control on the measurement quality, with the best results obtained using images at their original scale. Using these findings enabled designing an efficient and effective workflow for monitoring coastal topographic complexity at a large scale. [ABSTRACT FROM AUTHOR]

The dynamics of Mediterranean ephemeral channels (MEC) is an interesting geomorphological topic as the extrinsic and intrinsic factors influencing this geomorphic system have been exposed to important and recent changes. It is crucial to carry out studies of these systems at suitable temporal scales (e.g. decades) to understand the dynamics of the model and the adaptation to different perturbations. In this work, we test the suitability of archival aerial imagery and structure-from-motion photogrammetry (SfM) to produce 3D models and orthophotographs of MEC for different dates and to quantify morphological changes. Several reaches were selected from two representative MEC in the Segura River Catchment (Rambla de Algeciras y Rambla de Valdelentisco) and three from a MEC in the Ebro River Catchment (Barranco de Tudela). Archival aerial photographs from 1956 (dataset known as "vuelo americano B") and 1973-1986 (dataset known as "vuelo interministerial") together with natural ground control points (GCPs) surveyed by a Global Navigation Satellite System to fed SfM and produce point clouds, digital elevation models and orthophotographs. The classical SfM workflow was adapted to work with the archival aerial imagery, i.e. adding fiducial markers, masking the photographs, using of natural permanent GCPs, etc. The results showed a root mean square error in the cartographic products that varied from 0,62 to 0,85 m with volumetric point densities in the resulting point clouds from 1,03 to 4,47 pts·m-3. Hence, the proposed methodological approach may be used to quantify important geomorphic changes (>1 m), to characterize the morphology of MEC in the past and to include the resulting cartographic products with today spatial information for a better understanding of the dynamics. [ABSTRACT FROM AUTHOR]

• Cost-effective photogrammetry-based methodology for surveying historical structures. • Application of the technique to build the FEM model of an historical structure. • The 3D model considers 7 types of materials, including adobe and brick/stone masonry. • Non-linear pushover analysis and N2 method to evaluate the seismic response. • The results of the seismic assessment can pave the way for informed preservation. This research presents a cost-effective surveying methodology to assist the seismic assessment of complex heritage buildings, based on terrestrial structure-from-motion (SfM) photogrammetry. The method was applied to the study of the seismic performance of the church of San Juan Bautista – Inca temple of Huaytará, Peru, an emblematic case study due to its complex architecture and coexistence of different construction materials. The geometrical model for the seismic assessment was developed with an error of less than 2 % using SfM photogrammetry. Non-linear static pushover analyses were performed on 3D FEM models of the nave and the towers to evaluate their individual response under seismic loading. Mechanical properties of different structural materials of the church were evaluated based on laboratory experimental tests on mortar and adobe, contemporary and ancient fired brick, Inca stone, colonial stone and rubble stone units. Non-linear pushover analyses were conducted in four directions perpendicular to the perimeter walls, and the response of the structure was compared with the seismic demand specified in Peruvian Standards. The simulations show that damage-prone areas are the western and eastern facades, with cracking at the connections between orthogonal walls, as well as at the interface of adobe masonry with Inca stone masonry. The towers exhibit similar seismic response, with lower strength capacities compared to the main nave. In this case, flexural overturning mechanisms and cracking at the interface between stone and adobe masonry were observed. The displacement-based seismic assessment using the N2 method shows that a peak ground acceleration of 0.21 g could lead to the collapse of the north and south facades of the main nave. The towers showed a much smaller capacity with PGA leading to collapse of approximately 0.09 g. Overall, this study contributes to the understanding of the seismic performance of the Huaytará-Huancavelica church, highlighting vulnerabilities and providing valuable information for its preservation and future interventions. Future investigations should focus on on-site tests that will allow the estimation of the effect of existing damage on the structural response and their incorporation in the numerical model. [ABSTRACT FROM AUTHOR]

The Upper Rhone Valley (Valais, Switzerland) has been heavily modified over the past 200 years by human activity and natural processes. A qualitative analysis of the morphological and land-use evolution of the Rhone River floodplain since the end of the eighteenth century was carried out using historical maps from 1780 to 1860 processed with Structure-from-Motion (SfM) and Geographical Information System (GIS) tools. This study aims to produce a long-term analysis of river management and land-use change in a stretch of the Upper Rhone Valley around the town of Sion based on a time series of maps, realised in the years 1780–1802, 1820–1845, 1847, 1850s, 1852–1857, 1859–1860. The historical maps were digitised, and for each of the corresponding periods, a map was produced within a GIS. The comparison of the maps was completed by using documentary sources or subsequent studies. With the intention to identify the fluvial landscape changes and past river management, six multitemporal maps were produced. Finally, this research aims to provide helpful diachronic information for planning a future sustainable landscape development in Valais. [ABSTRACT FROM AUTHOR]

Ecological processes occur over multiple spatial, temporal and thematic scales in three-dimensional (3D) ecosystems. Characterizing and monitoring change in 3D structure at multiple scales is challenging within the practical constraints of conventional ecological tools. Remote sensing from satellites and crewed aircraft has revolutionized broad-scale spatial ecology, but fine-scale patterns and processes operating at sub-metre resolution have remained understudied over continuous extents. We introduce two high-resolution remote sensing tools for rapid and accurate 3D mapping in ecology—terrestrial laser scanning and structure-from-motion photogrammetry. These technologies are likely to become standard sampling tools for mapping and monitoring 3D ecosystem structure across currently under-sampled scales. We present practical guidance in the use of the tools and address barriers to widespread adoption, including testing the accuracy of structure-from-motion models for ecologists. We aim to highlight a new era in spatial ecology that uses high-resolution remote sensing to interrogate 3D digital ecosystems. [ABSTRACT FROM AUTHOR]

Globally, many ecosystems are being challenged and transformed by anthropogenic climate change. Future ecosystem configurations will be heavily influenced by the critical ecological functions that affect resilience. Robust measures of these functions will thus be essential for understanding and responding to ecological change.Coral reefs are experiencing unprecedented ecological change due to global mass coral bleaching. After bleaching events and other disturbances, herbivorous fishes provide functions that are critical for reef resilience by controlling harmful proliferation of algae. Identifying functional diversity amongst herbivorous fishes has been a mainstay of reef fish research, but it has remained unclear how, and to what extent, functional diversity translates to functional impacts on reefs.Rather than assessing the functional potential of the herbivorous fish community, we explicitly considered the delivery of herbivory to the reef by quantifying, in unprecedented detail, the spatial extent and overlap of feeding areas across different functional groups. Core feeding areas were highly concentrated and consistently covered just 14% of available reef space. Overlap across functional groups was limited, showing high spatial complementarity as functional groups tended to feed next to one another. Thus, the delivery of critical ecosystem processes was patchy, effectively reducing functional redundancy, even in the presence of a diverse fish assemblage.Our findings caution against assumptions of spatial homogeneity in the delivery of critical ecosystem functions. The functional impact of local herbivorous fish assemblages in current approaches may be overestimated, potentially leading to skewed assessments of reef resilience. Our results highlight the need to incorporate collective animal behaviour and spatio‐temporal scales into future assessments of ecosystem functions and ultimately ecological resilience. A plain language summary is available for this article. [ABSTRACT FROM AUTHOR]

Along the rugged coast of Big Sur, California, the Mud Creek landslide failed catastrophically on May 20, 2017, and destroyed over 400 m of scenic California State Highway 1. We collected structure-from-motion (SfM) photogrammetry data using airborne platforms that, when combined with existing airborne lidar data, revealed that the area exhibited significant topographic change and displacement before, during, and after the catastrophic failure. Before the catastrophic failure, we document two areas of elevated change in the zone of depletion, which aligned with the double-peaked head scarp produced by the catastrophic failure. The catastrophic failure extended from 337-m elevation to at least 8 m below sea level, was 490 m wide, displaced ~ 3 million m3 of earth and rock, and deposited landslide debris at least 175 m seaward of the original shoreline. The failure was not a complete slope-clearing event, however, and several upslope and lateral regions that did not slip into the ocean exhibited significant displacement and topographic change during the days and months after the catastrophic failure. Additionally, we use the post-slide data to quantify several other processes, including the time-varying rates of talus accumulation and coastal erosion of the landslide toe. We conclude that repeat SfM surveys from aerial imagery can provide valuable information about landslide evolution and the potential for deep-seated landslide hazards—especially in the lead up to catastrophic failure—if photos are collected and processed regularly. [ABSTRACT FROM AUTHOR]

Grasslands deliver a range of ecosystem services, including the provision of food and biodiversity, and regulation of soil carbon storage and hydrology. Monitoring schemes are needed to quantify spatial changes in these multiple functions alongside ecosystem degradation. Sward height is widely recognised as a key spatial variable in the provision of these services. Current manual monitoring approaches are labour intensive, and often fail to capture spatial patterns of important features, including sward height.Proximal sensing from small aerial drones carrying lightweight cameras can be transformed into surface height models using image‐based structure‐from‐motion and Multi‐View Stereo‐based approaches; this presents a new opportunity for monitoring the spatial structure of grassland sward height. We combined aerial photographs with field survey data and an open‐source image‐based modelling‐processing workflow to generate sward height measurements for a field comprising mainly Lolium perenne (perennial ryegrass) and Trifolium pratense (red clover). We compared the derived measurements with in situ data captured on the same day using traditional agronomic sward height techniques to determine the quality of the drone‐derived surface model product for sward characterisation.The SfM and Multi‐View Stereo‐based surface model had a mean absolute sward height measurement error of between 3.7 and 4.2 cm. To produce field observations with equivalent quality would require up to 550 sward height measurements for the study site (area: 8,059 m2), which is not feasible over larger extents required for conservation of key species or agronomic purposes.Synthesis and applications. We demonstrate how the collection of precise and detailed information on the spatial structure of grasslands can be made over management‐relevant extents. Aerial digital photographs can be transformed into surface models using an image‐based modelling approach: structure‐from‐motion and Multi‐View Stereo techniques. Image‐based measurements of sward heights were compared with manual sward height data captured on the same day. This novel source of vegetation spatial information could improve sward management for conservation and agronomy applications. The approach supports frequent surveys, at user‐controlled revisit times, and delivers data for spatial monitoring of key grassland functions and services. We demonstrate how the collection of precise and detailed information on the spatial structure of grasslands can be made over management‐relevant extents. Aerial digital photographs can be transformed into surface models using an image‐based modelling approach: structure‐from‐motion and Multi‐View Stereo techniques. Image‐based measurements of sward heights were compared with manual sward height data captured on the same day. This novel source of vegetation spatial information could improve sward management for conservation and agronomy applications. The approach supports frequent surveys, at user‐controlled revisit times, and delivers data for spatial monitoring of key grassland functions and services. [ABSTRACT FROM AUTHOR]

Abstract The subglacial hydrology of tidewater glaciers is a key but poorly understood component of the complex ice-ocean system, which affects sea level rise. As it is extremely difficult to access the interior of a glacier, our knowledge relies mostly on the observation of input variables such as air temperature, and output variables such as the ice flow velocities reflecting the englacial water pressure, and the dynamics of plumes reflecting the discharge of meltwater into the ocean. In this study we use a cost-effective Vertical Take-Off and Landing (VTOL) Unmanned Aerial Vehicle (UAV) to monitor the daily movements of Bowdoin Glacier, north-west Greenland, and the dynamics of its main plume. Using Structure-from-Motion photogrammetry and feature-tracking techniques, we obtained 22 high-resolution ortho-images and 19 velocity fields at the calving front for 12 days in July 2016. Our results show a two-day-long speed-up event (up to 170%) – caused by an increase in buoyant subglacial forces – with a strong spatial variability revealing that enhanced acceleration is an indication of shallow bedrock. Further, we used the Particle Image Velocimetry (PIV) method to analyze water flow from successive UAV images taken while flying over the main plume of the glacier. We found that PIV successfully captures the area of radially diverging flow of the plume, and provides information on spatial and time variability as no other remote sensing technique can. Most interestingly, the active part of the plume features pulsating water jets at the time scale of seconds, and is 1 to 5 times smaller than its visual footprint defined by the iceberg-free area. Combined with an ice flow model or a non-steady plume model, our approach has the potential to generate a novel set of input data to gather information about the depth of the bedrock, the discharge of meltwater, or the subglacial melting rate of tidewater glaciers. Highlights • First use of a VTOL UAV for glacier monitoring • First use of Particle Image Velocimetry (PIV) to infer meltwater plume flow • A major short-lived ice speed-up event of a calving glacier is captured. • PIV results evidence of the unsteady nature of the plume dynamics. • Ice and plume flows give insights into subglacial hydrological system. [ABSTRACT FROM AUTHOR]

River bank erosion is controlled by a complex combination of factors and processes that play a main role in fluvial dynamics. However, the role played by lateral erosion in small low energy rivers functioning still needs to be better understood. This study deals with the characterization and the quantification of the bank erosion of a small low energy river of the Seine Basin (France) in periurban catchment where urbanization had led to an incision and widening of the bed in the past decades, using adapted monitoring surveys: erosion pins and Structure-from-Motion Photogrammetry. The paper provides an opportunity to compare reach-scale flux estimates using both techniques. Spatial and temporal variations in river bank rates were quantified over 16 months and the causes and controls of riverbank erosion were identified. The estimated morphological activity rate ranges from 117 cm/yr to 1 cm/yr, illustrating the very heterogeneous spatio-temporal pattern of bank erosion observed on the Merantaise River. Whereas a number of studies consider subaerial processes as the dominant processes, fluvial erosion was found to be the most significant causal process, and in particular the mean discharge of floods. However, the high local variability of the bank erosion of the studied river appears to be controlled by very local factors such as the bank angle, the presence of a berm at the bank-toe (providing protection against fluvial erosion), lateral supply (outlet of rainwater pipes) and deflected flow in the direction of the bank. [ABSTRACT FROM AUTHOR]

Lodging has been recognized as one of the major destructive factors for crop quality and yield, resulting in an increasing need to develop cost-efficient and accurate methods for detecting crop lodging in a routine manner. Using structure-from-motion (SfM) and novel geospatial computing algorithms, this study investigated the potential of high resolution imaging with unmanned aircraft system (UAS) technology for detecting and assessing lodging severity over an experimental maize field at the Texas A&M AgriLife Research and Extension Center in Corpus Christi, Texas, during the 2016 growing season. The method was proposed to not only detect the occurrence of lodging at the field scale, but also to quantitatively estimate the number of lodged plants and the lodging rate within individual rows. Nadir-view images of the field trial were taken by multiple UAS platforms equipped with consumer grade red, green, and blue (RGB), and near-infrared (NIR) cameras on a routine basis, enabling a timely observation of the plant growth until harvesting. Models of canopy structure were reconstructed via an SfM photogrammetric workflow. The UAS-estimated maize height was characterized by polygons developed and expanded from individual row centerlines, and produced reliable accuracy when compared against field measures of height obtained from multiple dates. The proposed method then segmented the individual maize rows into multiple grid cells and determined the lodging severity based on the height percentiles against preset thresholds within individual grid cells. From the analysis derived from this method, the UAS-based lodging results were generally comparable in accuracy to those measured by a human data collector on the ground, measuring the number of lodging plants (R² = 0.48) and the lodging rate (R² = 0.50) on a per-row basis. The results also displayed a negative relationship of ground-measured yield with UAS-estimated and ground-measured lodging rate. [ABSTRACT FROM AUTHOR]

The field of photogrammetry has seen significant new developments essentially related to the emergence of new computer-based applications that have fostered the growth of the workflow technique called Structure-from-Motion (SfM). Low-cost, user-friendly SfM photogrammetry offers interesting new perspectives in coastal and other fields of geomorphology requiring high-resolution topographic data. The technique enables the construction of topographic products such as digital surface models (DSMs) and orthophotographs, and combines the advantages of the reproducibility of GPS surveys and the high density and accuracy of airborne LiDAR, but at very advantageous cost compared to the latter. Three SfM-based photogrammetric experiments were conducted on the embayed beach of Montjoly in Cayenne, French Guiana, between October 2013 and 2014, in order to map morphological changes and quantify sediment budgets. The beach is affected by a process of rotation induced by the alongshore migration of mud banks from the mouths of the Amazon River that generate spatial and temporal changes in wave refraction and incident wave angles, thus generating the reversals in longshore drift that characterise this process. Sub-vertical aerial photographs of the beach were acquired from a microlight aircraft that flew alongshore at low elevation (275 m). The flight plan included several parallel flight axes with an overlap of 85% between pictures in the lengthwise direction and 50% between paths. Targets of 40 × 40 cm, georeferenced by RTK-DGPS, were placed on the beach, spaced 100 m apart. These targets served in optimizing the model and in producing georeferenced 3D products. RTK-GPS measurements of random points and cross-shore profiles were used to validate the photogrammetry results and assess their accuracy. We produced dense point clouds with 150 to 200 points/m², from which we generated DSMs and orthophotos with respective resolutions of 10 cm and 5 cm. Compared to the GPS control points, we obtained a mean vertical accuracy less than ± 10 cm, with a maximum of 20 cm in marginal sectors with sparse vegetation and in the lower intertidal zone where water-saturated surfaces generated lower-resolution data as a result of a lack of coherence between photographs. The overall results show that SfM photogrammetry is a robust tool for beach morphological and sediment budget surveys. Our SfM workflow enabled the discrimination of beach surface features at a scale of a few tens of centimetres despite the low textural contrasts exhibited by the quartz beach sand and the relatively uniform upper beach topography, as well as the calculation of beach sediment budgets. 66,000 m³ of sand were removed from the northern sector of the beach, of which 22,000 m³ were transferred to the southern sector in the course of rotation. Finally, we briefly highlight: (1) the advantages of SfM photogrammetry compared to other high-resolution survey methods, (2) the advantages and disadvantages of, respectively, a microlight aircraft and an unmanned aerial vehicle (UAV) in undertaking SfM photogrammetry, and (3) areas of potential future improvement of the SfM workflow technique. These concern more extensive cross-shore deployment of ground control points to reduce possible tilt, and oblique cross-shore photography to improve parallax. [ABSTRACT FROM AUTHOR]

• Collate nine high-resolution habitat complexity metrics for coral reefscapes. • Complexity uniquely drives intra-habitat variation in 7 trait-based fish functional groups. • Vertical relief increases richness and abundance for five of seven fish groups. • Gregariousness modulates effects of VRM and VRM deviation on herbivores. • Trait-based measures facilitate global prediction amidst habitat change. Three-dimensional (3D) habitat complexity is a primary driver of organism distribution and community structure across ecosystems. Identifying the specific metrics and spatial scales at which complexity is functionally important for communities is therefore a critical component in forecasting ecosystem function. Here we pair fish species traits with multiple metrics from habitat photogrammetry to evaluate the most important measures and scales of 3D complexity driving ecological functions within one of the most structurally diverse ecosystems on the planet: coral reefs. From May to July 2019, we collected high-resolution (1 cm) large- and small-scale intra-habitat (25 m2) structural complexity data across eight reefscapes (∼2500 m2) and conducted co-located fish functional group surveys in the Florida Keys, FL, USA. We used a hierarchical clustering analysis to group 80 observed fish species by four traits related to habitat use (social level, body size, crypsis, activity period) and feeding guild to generate mechanistic predictions about fish-habitat relationships. Evaluating relationships between the resulting trait-based functional groups (k = 9) and four metrics of intra-habitat complexity (large-scale vertical relief, and small-scale vector ruggedness [VRM], VRM deviation, and profile curvature) revealed that trait groups respond independently to the various measures and scales of reef complexity. While large-scale complexity (relief) is strongly related to the presence of solitary, cryptic, nocturnal carnivores, likely due to prey availability as well as day-time refuge opportunities, herbivore abundance is unaffected by increasing vertical relief, potentially due to predator avoidance. Instead, gregarious (i.e., schooling) herbivores increase with small-scale complexity measured by VRM and VRM deviation across reefscapes, while less gregarious herbivores only respond to small-scale complexity when these same measures occur in low-relief habitat, possibly due to a tradeoff between grazing resource availability and predator visibility. Our results reveal how unique elements of complexity provided by both biotic benthic communities as well as large-scale habitat features like vertical relief are differentially important to fish functional groups. The general relationships we identified using traits provide a framework for predicting fish community responses to changes in specific measures of structural complexity on coral reefs globally. Our work illustrates how preserving 3D habitat complexity by protecting or augmenting (e.g., via restoration) structure-forming organisms can support diverse organismal communities and overall ecosystem productivity. [ABSTRACT FROM AUTHOR]

Camping in the mountain regions has several negative impacts, including soil erosion in the campsites. In many national parks, efforts to monitor and manage campsite soil erosion are insufficient or even lacking. Owing to the lack of implementation of formal management practices, the current and former Kuro-dake campsites in Daisetsuzan National Park (DNP) have suffered serious soil erosion. To gain more insights into campsite soil erosion, we investigated these two campsites by short-term monitoring through structure-from-motion (SfM) photogrammetry surveys with ground control points (GCPs). These surveys were conducted three times consecutively in the current (2017, 2018, and 2019) and former Kuro-dake campsites (2018, 2019, and 2020). Two sets of digital elevation models (DEMs) of the current and former campsites were produced with the resolutions of 0.015 and 0.025 m, respectively. We detected that the elevation changes exceeded by 0.03–0.04 m, using the DEMs of difference (DoDs) maps. Soil loss around the gullies was observed at each campsite. In the current campsite, soil losses of 2.20 and 0.30 m3 were identified in the periods of 2017–2018 and 2018–2019, respectively. In the former campsite, soil losses of 1.55 and 22.27 m3 were identified during 2018–2019 and 2019–2020, respectively. In addition, a large amount of exposed mineral soil with exposed rocks was observed at each campsite. Various erosion rates obtained in the short-term study indicated the importance of continuous monitoring. High-resolution and high-accuracy topographic products generated from the SfM photogrammetry survey enabled the detection of a small amount of campsite soil erosion and provided a new method to monitor campsite degradation. This study demonstrated that a simple closure of the former campsite in 1992 failed to reduce the impact of soil erosion. In the case of the current and former Kuro-dake campsites, burying the gullies with boulders and setting up boulders or wood fences at the termini of the gullies would be a potential solution to stop or mitigate further erosion. Thus, formal management including monitoring and maintenance of site conditions should be introduced to Kuro-dake as well as other unmanaged campsites in DNP. • Repeat SfM surveys can detect even low magnitude of soil erosion, which occurred on the campsite. • The closed campsite is still suffering from a large amount of soil loss. • More soil loss was observed around the gullies than other parts on the campsite. [ABSTRACT FROM AUTHOR]

In sandy environments, like the beach-dune system, buildings not only affect the airflow, but also the aeolian sediment transport in their surroundings. In this study, we determine how the horizontal size of sediment deposition patterns around buildings depends on the building's dimensions. Four one-day experiments were conducted at the beach using box-shaped scale models. We tested 32 building geometries, where scale model height, width and length ranged between 0.3 and 2.0 m. The deposition patterns were substantial in size: the total length and width of the deposition area were up to an order of magnitude larger than the horizontal building dimensions. It was found that the size of upwind and downwind deposition patterns depended more on the building width perpendicular to the wind direction (w), than on the building height (h). Building length had little influence. Especially the combined effect of w and h correlated well with horizontal deposition size. This is expressed in a new scaling length B for deposition around buildings, with B = w 2 / 3 · h 1 / 3. As a first validation, the spatial dimensions of the initial deposition patterns observed around a scale model of 2.5 × 12 × 2.5 m, placed at the beach for five weeks, showed good agreement with those predicted based on B. • Outdoor scale experiments successfully captured aeolian sand dynamics. • Horizontal deposition dimensions can be ten times larger than the building dimensions. • Building width and height determine the horizontal size of deposition patterns. • A characteristic building length scale links building size to aeolian deposition size. [ABSTRACT FROM AUTHOR]

This paper presents a framework for the three-dimensional structural analysis of full scale, geometrically complex rubble masonry structures from point clouds generated from Structure-from-Motion photogrammetry or terrestrial laser scanning. According to the method, a point-based voxelization algorithm was adopted, whereby a dense point cloud was down-sampled into equidistant points, bypassing the need for conventional intensive processes, such as watertight mesh conversion, to obtain the geometric model of the rubble masonry for structural analysis. The geometry of the rubble masonry structure was represented by a sum of hexahedral rigid blocks (voxels). The proposed " point cloud to structural analysis " framework was implemented to assess the structural stability of the southwest leaning tower of Caerphilly Castle in Wales, UK. Simulations were performed with the three- dimensional computational software 3DEC, based on the Discrete Element Method (DEM) of analysis. Each voxel of the rubble masonry was represented as a rigid, distinct block while mortar joints were modelled as zero thickness interfaces which can open and close depending on the magnitude and direction of the stresses applied to them. The potential of the automated procedure herein proposed has been demonstrated to quantitatively assess the three-dimensional mechanical behaviour rubble masonry structures and provide valuable information to asset owners in relation to the structural health condition of assets in their care. • A procedure for DE modelling of rubble masonry from point clouds is proposed. • Rubble geometry represented by hexahedral rigid blocks bonded together. • The stability of the leaning tower of Caerphilly Castle evaluated. • The procedure presents a high degree of automation at each operational level. [ABSTRACT FROM AUTHOR]

The alluvial channel of the Langgriesgraben (Austria) is a highly active geomorphic riverine subcatchment of the Johnsbach River with intermittent discharge and braided river structures. The high sediment yield entails both issues and opportunities. For decades, the riverbed was exploited as a gravel pit. Today, as part of the Gesäuse National Park and after renaturation, the sediment yield endangers a locally important bridge located at the outlet of the subcatchment. High-resolution geospatial investigations are vital for the quantification of sediment redistribution, which is relevant in terms of river management. Based on unmanned aerial system (UAS) surveys in 2015 (July, September, and October) and 2019 (August and October), high-resolution digital elevation models (DEMs) were generated, which enable us to quantify intra- and multiannual sediment changes. As surface runoff at the subcatchment occurs on only a few days per year with flash floods and debris flows that are not predictable and thus hardly observable, the subsurface water conditions were assessed based on electrical resistivity tomography (ERT) measurements, which were conducted in 2019 (November) and 2020 (May, June). Results of the UAS-based surveys showed that, considering the data quality, intra-annual sediment changes affected only small subareas, whereas multiannual changes occurred in the entire study area and amount to net sediment deposition of ≈0.3–0.4 m3m−2, depending on the channel section. In addition, the elevation differences for both intra-annual surveys revealed linear patterns that can be interpreted as braided river channels. As in both survey periods the same areas were affected by changes, it can be concluded that the channel mainly affected by reshaping persisted within the 4-year observation period. The subsurface investigations showed that although both near-surface and groundwater conditions changed, near-surface sediments are mostly dry with a thickness of several meters during the observations. [ABSTRACT FROM AUTHOR]

Rockfalls and rockslides are often dominant geomorphic processes in steep bedrock landscapes, but documenting their occurrence can be challenging, requiring frequent monitoring and well resolved spatial data. Repeat application of remote sensing methods such as Terrestrial Laser Scanning (TLS) and Structure-from-Motion (SfM) photogrammetry can detect even very small rockfalls, but typically these acquisitions span only years and may not record rockfall activity representative of longer-term rates of cliff erosion. Inventory databases can extend rockfall records, but are commonly incomplete and prone to observation bias. We employed TLS and SfM on two adjacent cliffs (El Capitan and Middle Brother) in Yosemite Valley, integrating semi-annual data collections from 2010 to 2017 with "historical" (archival) SfM models derived from oblique photographs taken in 1976. Comparing the 1976 SfM models against more recent data allows for more accurate and precise rockfall detection and volume measurement over a 40-year period. Change detection indicates that 235 rockfalls occurred from the two cliffs, more than twice as many events as are recorded in Yosemite's inventory database. Although individual rockfall volumes reported in the inventory database vary from those measured by SfM-TLS, reported cumulative volumes are similar to measured volumes, likely because the large-volume events that account for most of the cumulative volume tend to be widely observed and well-documented. Volume-frequency relationships indicate that the cliffs erode predominantly by less frequent, larger-volume rockfalls, at rates of 0.9 to 1.7 mm/yr. Our study demonstrates how integrated SfM and TLS measurements, especially utilizing SfM models derived from historical imagery, allow detection and quantification of rockfalls spanning several decades, complementing and improving inventory databases, informing rockfall hazard assessment, and providing longer-term rates of cliff erosion. • 1976's photographs yielded high-resolution models of two cliffs in Yosemite Valley. • "Historical" models were compared to terrestrial lidar data acquired in 2010/2016. • 235 rockfalls were detected from the two monitored cliffs over a 40-year period. • Both cliffs experienced twice as many rockfalls as are recorded in the database. • Rockfall volume-frequency relationships indicate erosion rates of 0.9 to 1.7 mm/yr. [ABSTRACT FROM AUTHOR]

Much of the geomorphic work of rivers occurs underwater. As a result, high resolution quantification of geomorphic change in these submerged areas is important. Currently, to quantify this change, multiple methods are required to get high resolution data for both the exposed and submerged areas. Remote sensing methods are often limited to the exposed areas due to the challenges imposed by the water, and those remote sensing methods for below the water surface require the collection of extensive calibration data in-channel, which is time-consuming, labour-intensive, and sometimes prohibitive in difficult-to-access areas. Within this paper, we pioneer a novel approach for quantifying above- and below-water geomorphic change using Structure-from-Motion photogrammetry and investigate the implications of water surface elevations, refraction correction measures, and the spatial variability of topographic errors. We use two epochs of imagery from a site on the River Teme, Herefordshire, UK, collected using a remotely piloted aircraft system (RPAS) and processed using Structure-from-Motion (SfM) photogrammetry. For the first time, we show that: (1) Quantification of submerged geomorphic change to levels of accuracy commensurate with exposed areas is possible without the need for calibration data or a different method from exposed areas; (2) there is minimal difference in results produced by different refraction correction procedures using predominantly nadir imagery (small angle vs. multi-view), allowing users a choice of software packages/processing complexity; (3) improvements to our estimations of water surface elevations are critical for accurate topographic estimation in submerged areas and can reduce mean elevation error by up to 73%; and (4) we can use machine learning, in the form of multiple linear regressions, and a Gaussian Naïve Bayes classifier, based on the relationship between error and 11 independent variables, to generate a high resolution, spatially continuous model of geomorphic change in submerged areas, constrained by spatially variable error estimates. Our multiple regression model is capable of explaining up to 54% of magnitude and direction of topographic error, with accuracies of less than 0.04 m. With on-going testing and improvements, this machine learning approach has potential for routine application in spatially variable error estimation within the RPAS–SfM workflow. [ABSTRACT FROM AUTHOR]

Snow depth estimation derived from high-resolution digital elevation models (DEMs) can lead to improved understanding of the spatially highly heterogeneous nature of snow distribution, as well as help us improve our knowledge of how snow patterns influence local geomorphic processes. Slope deformation processes such as permafrost creep can make it challenging to acquire a snow-free DEM that matches the sub-snow topography at the time of the associated snow-covered DEM, which can cause errors in the computed snow depths. In this study, we illustrate how modelling changes in the sub-snow topography can reduce errors in snow depths derived from DEM differencing in an area of permafrost creep. To model the sub-snow topography, a surface deformation model was constructed by performing non-rigid registration based on B-splines of two snow-free DEMs. Seasonal variations in creep were accounted for by using an optimization approach to find a suitable value to scale the deformation model based on in-situ snow depth measurements or the presence of snow-free areas corresponding to the date of the snow-covered DEM. This scaled deformation model was used to transform one of the snow-free DEMs to estimate the sub-snow topography corresponding to the date of the snow-covered DEM. The performance of this method was tested on an active rock glacier in the southern French Alps for two surveys dates, which were conducted in the winter and spring of 2017. By accounting for surface displacements caused by permafrost creep, we found that our method was able to reduce the errors in the estimated snow depths by up to 33% (an interquartile range reduction of 11 cm) compared to using the untransformed snow-free DEM. The accuracy of the snow depths only slightly improved (root-mean-square error decrease of up to 3 cm). Greater reductions in error were observed for the snow depths calculated for the date that was furthest (i.e., the winter survey) in time from the snow-free DEM. Additionally, we found that our approach to scaling the deformation model has promising potential to be adapted for monitoring seasonal variations in permafrost creep by combining in-situ snow depth measurements with high-resolution surface deformation models. • Errors in DEM derived snow depth can be reduced using a surface deformation model. • Non-rigid registration based on B-splines can accurately model permafrost creep. • Seasonal variations in creep can be estimated with several optimization approaches. [ABSTRACT FROM AUTHOR]

Complex landscapes with high topographic relief and intricate geometry present challenges for complete and accurate mapping of both lateral (x, y) and vertical (z) detail without deformation. Although small uninhabited/unmanned aerial vehicles (UAVs) paired with structure-from-motion (SfM) image processing has recently emerged as a popular solution for a range of mapping applications, common image acquisition and processing strategies can result in surface deformation along steep slopes within complex terrain. Incorporation of oblique (off-nadir) images into the UAV–SfM workflow has been shown to reduce systematic errors within resulting models, but there has been no consensus or documentation substantiating use of particular imaging angles. To address these limitations, we examined UAV–SfM models produced from image sets collected with various imaging angles (0–35°) within a high-relief 'badland' landscape and compared resulting surfaces with a reference dataset from a terrestrial laser scanner (TLS). More than 150 UAV–SfM scenarios were quantitatively evaluated to assess the effects of camera tilt angle, overlap, and imaging configuration on the precision and accuracy of the reconstructed terrain. Results indicate that imaging angle has a profound impact on accuracy and precision for data acquisition with a single camera angle in topographically complex scenes. Results also confirm previous findings that supplementing nadir image blocks with oblique images in the UAV–SfM workflow consistently improves spatial accuracy and precision and reduces data gaps and systematic errors in the final point cloud. Subtle differences among various oblique camera angles and imaging patterns suggest that higher overlap and higher oblique camera angles (20–35°) increased precision and accuracy by nearly 50% relative to nadir-only image blocks. We conclude by presenting four recommendations for incorporating oblique images and adapting flight parameters to enhance 3D mapping applications with UAV–SfM in high-relief terrain. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Icebergs and ice islands (large, tabular icebergs) are challenging targets to survey due to their size, mobility, remote locations, and potentially difficult environmental conditions. Here, we assess the precision and utility of aerial photography surveying with structure-from-motion multi-view stereo photogrammetry processing (SfM) and vessel-based terrestrial laser scanning (TLS) for iceberg deterioration detection and mass estimation. For both techniques, we determine the minimum amount of change required to reliably resolve iceberg deterioration, the deterioration detection threshold (DDT), using triplicate surveys of two iceberg survey targets. We also calculate their relative uncertainties for iceberg mass estimation. The quality of deployed Global Positioning System (GPS) units that were used for drift correction and scale assignment was a major determinant of point cloud precision. When dual-frequency GPS receivers were deployed, DDT values of 2.5 and 0.40 m were calculated for the TLS and SfM point clouds, respectively. In contrast, values of 6.6 and 3.4 m were calculated when tracking beacons with lower-quality GPS were used. The SfM dataset was also more precise when used for iceberg mass estimation, and we recommend further development of this technique for iceberg-related end-uses. [ABSTRACT FROM AUTHOR]