Surface Elevation Model Research Articles

The Megaliths of Mols Peninsula – a Case Study of Applied Digital Photogrammetry in a Survey of Neolithic Monuments in Denmark

Abstract This study presents a practical case analysis detailing the outcomes of a survey project conducted on Neolithic megalithic structures on the Mols Peninsula in East Jutland, Denmark. The survey methodology employed digital photogrammetry, utilizing consumer-grade drones and handheld digital cameras. This approach facilitated the merging of aerial perspectives of the local surroundings with terrestrial photographs specifically focusing on the densely clustered stone chambers. Subsequently, the gathered data underwent conversion into various forms, such as orthophotos, surface elevation models, 3D representations, hill shades, point clouds, and textured low-resolution models optimized for online visualization. Among the noteworthy findings, the study included an evaluation of 19th-century drawings, revealing their remarkable precision. However, it was also noted that one of the monuments underwent substantial alterations in 1943. Moreover, the study successfully generated 3D models of the capstones from two dolmens, allowing for their virtual reconstruction. Importantly, the research introduced an innovative technique for mapping burned flints on the field surface surrounding the dolmens by employing low-altitude vertical drone photography – a previously unexplored method.

Reconstruction of ancient drainage in the contact karst of the Harmanecká dolina Valley, Western Carpathians, based on mineralogical data from the allochthonous sediments and isobase geomorphometry

AbstractCaves are unique sedimentary archives that may record the evolution of the surrounding landscape. In this study, we applied combination of mineralogical data on allochthonous sediments with digital modelling of isobase surfaces to reconstruct the multi‐phased geomorphological development of the karst of the Harmanecká dolina Valley. The allochthonous cave sediments contain quartz and translucent heavy minerals (HMs) such as tourmaline, garnet, rutile, apatite, zircon, pyroxene, amphibole, staurolite, spinel, monazite, corundum, epidote, xenotime and florencite. Rounded shape and surface microtextures preserved on quartz and most HM grains point to predominantly a fluvial transport of detritus and its multiple recycling history. Pyroxene and amphibole are exceptions that denoted a very close source and the first‐cycle sedimentation from the adjacent volcanic Kremnické vrchy Mts. corresponding to obtained SHRIMP U–Pb detrital zircon ages of ~13.8–12.8 Ma. Heavy‐mineral geochemistry (e.g., zoned grossular‐rich garnet) and wide range of the Palaeozoic ages (Ordovician to Permian) confirms that the studied detritus sourced dominantly in the Western‐Carpathian crystalline basement rocks of the Veporic/Tatric tectonic units initially distributed by the palaeo‐Hron River and its tributaries from the east. Rare cummingtonite, remarkable tourmaline with omphacite inclusions and florencite point to the mixture of recycled sediments of Neogene Danube Basin formations containing also Austroalpine pre‐Neogene basement detritus, and confirm the original widespread distribution of the Neogene sediments currently eroded. Geomorphometric analyses of a LiDAR digital terrain model and derived isobase surface elevation models indicate the topographic development of wider area and support the findings about the transport direction of detritus. Presented multi‐method approach is suitable not only for the understanding of development of the surroundings of Harmanecká dolina Valley but also for the palaeogeographic and geomorphological reconstructions of similar karst and non‐karst areas.

Use of unmanned aerial vehicle (UAV) in the analysis of natural risks: Landslides in the Ancoa Reservoir Sector, Linares Province, Maule Region.

On July 20, 2022 at 9:00 p.m., a landslide-type mass removal was recorded on route L-39, specifically at km 30.7 of the area of the first viewpoint of the Ancoa Reservoir, which is frequented by residents and visitors who come to this tourist sector. The landslide generated a road cut of 200 m, with the affected area of the hillside approximately 5,251 m2. UAV (Unmanned Aerial Vehicle) flight was carried out in the study area, to obtain geographic information, data collection and geomorphological surface processes of the landslide, based on orthophoto measurements and generation of surface elevation models (DSM). The results show that photogrammetry from UAVs provides flexible and effective tools to evaluate and analyze geomorphological characteristics, in addition to mapping and monitoring this type of mass removal, being the basis for generating multitemporal studies.

Application of Finite Element Method to Create a Digital Elevation Model

The generation of a topographical surface or digital elevation model for a given set of points in space is a known problem in civil engineering and topography. In this article, we propose a simple and efficient way to obtain the terrain surface by using a structural shell finite element model, giving advice on how to implement it. The proposed methodology does not need a large number of points to define the terrain, so it is especially suitable to be used with data provided by manual topographical tools. Several examples are developed to demonstrate the easiness and accuracy of the methodology. The digital terrain model of a real landscape is modeled by using different numbers of points (from 49 to 400) using a regular mesh or a randomly generated cloud of points. The results are compared, showing how the proposed methodology creates a sufficiently accurate model, even with a low number of points (compared with the thousands of points handled in a LiDAR representation). A real case application is also shown. As an appendix, the sample code to generate the examples is provided.

High-resolution bathymetries and shorelines for the Great Lakes of the White Nile basin

HRBS-GLWNB 2020 presents the first open-source and high-resolution bathymetry, shoreline, and water level data for Lakes Victoria, Albert, Edward, and George in East Africa. For each Lake, these data have three primary products collected for this project. The bathymetric datasets were created from approximately 18 million acoustic soundings. Over 8,200 km of shorelines are delineated across the three lakes from high-resolution satellite systems and uncrewed aerial vehicles. Finally, these data are tied together by creating lake surface elevation models collected from GPS and altimeter measures. The data repository includes additional derived products, including surface areas, water volumes, shoreline lengths, lake elevation levels, and geodetic information. These data can be used to make allocation decisions regarding the freshwater resources within Africa, manage food resources on which many tens of millions of people rely, and help preserve the region’s endemic biodiversity. Finally, as these data are tied to globally consistent geodetic models, they can be used in future global and regional climate change models.

APPLICATIONS OF PHOTOGRAMMETRY TO NEOICHNOLOGICAL STUDIES: THE SIGNIFICANCE OF SHOREBIRD TRACKWAY DISTRIBUTIONS AT THE BAY OF FUNDY

Abstract Low-level drone photogrammetry is a technique that allows for the construction of surface orthomosaics and elevation models. Despite being used for a wide range of geological applications, these types of datasets have not yet been explored from a neoichnological perspective. This study uses three examples of tidal flats from the Bay of Fundy to demonstrate the usefulness of 3D photogrammetry in the collection of high-resolution neoichnological datasets. The first site is a bar top along the Petitcodiac River that is situated between a salt marsh and tidal channel margin. The second site, which is located along the Shepody River, represents a laterally accreting channel margin and thus has a relatively high relief. In contrast, the final site comprises a gently sloping tidal flat that is far from the influence of a major tidal channel. Spatial analysis of the shorebird tracks at each site was used to assess the relationship between shorebird track distributions (e.g., track density, stride orientation, stride length) and various environmental and ecological factors (e.g., topography, tidal current direction, invertebrate prey distributions). Additionally, morphological analysis of the tracks was used to assess variations in substrate cohesiveness, which is the environmental factor that exhibited the most variability at the study locations. The track record at each site represents a shorebird flock that traversed the tidal flats in such a way as to optimize foraging success. As a result, the abundance and availability of macrobenthic invertebrate prey was the primary factor contributing to shorebird track density. This paper aims to assess local-scale variations in tidal flat substrate cohesiveness and provide context for the interpretation of fossilized shorebird trackways.

Late Holocene rupture history of the Ash Hill fault, Eastern California Shear Zone, and the potential for seismogenic strain transfer between nearby faults

AbstractUnderstanding how fault systems interact and transfer strain over seismogenic timescales (seconds to ka) requires temporal records of past ruptures along adjacent and intersecting fault networks. Here we document the record of Late Holocene ruptures as recorded in the geomorphology of alluvial deposits along the Ash Hill fault, in the Eastern California Shear Zone (ECSZ). We leverage a multi‐faceted approach to evaluate the relative timing of Ash Hill fault ruptures to those of nearby faults in the ECSZ. We determine the number and timing of Late Holocene earthquakes on the Ash Hill fault using high‐resolution tectono‐geomorphic mapping, a locally calibrated alluvial fan stratigraphy, feldspar luminescence dating, and fault offset analysis from field observations, LiDAR, and drone‐based digital surface elevation models. We find evidence for three surface‐rupturing earthquakes that have occurred since ~4 ka, each with ~1.0 ± 0.2 m of oblique slip per event (Mw ~ 6.9–7.0), and we constrain the timing of these earthquakes by dating deposits that bracket each event. The timing of these three ruptures is similar to the paleoseismic record along the adjacent range‐bounding fault in southern Panamint Valley. Specifically, the two adjacent faults exhibit similar numbers of earthquakes during the Late Holocene, with similar recurrence intervals and rupture timing. These data suggest that it is possible that these two faults have ruptured in the same or closely temporally related events throughout the Late Holocene. Similar spatio‐temporal clustered earthquakes have been recognized in both historic and paleoseismic records in the region, and such behaviour may be common in complexly interlinked fault networks, like those that exist in the ECSZ.

Bedrock surface topography of Latvia

ABSTRACT A new map and digital bedrock surface elevation model of Latvia is presented with a horizontal resolution of 250 m. The local bedrock comprises largely undisturbed layers of Palaeozoic and Mesozoic sedimentary rocks covered by up to 200 m thick Quaternary strata composed mostly of glacigenic and marine sediments. The bedrock surface elevation model and the corresponding map were created by tessellation interpolation of the bedrock surface based on more than 20,000 boreholes and constrained by the present land surface. The known locations of paleo-incisions buried under Quaternary cover are indicated. The new digital map has applications in hydrogeological, environmental, and civil engineering, and fundamental and applied research.

Ice Dynamics and Morphological Changes During Proglacial Lake Development at Exploradores Glacier, Patagonia

Proglacial lakes are ubiquitous features formed during deglaciarization and are currently increasing in number in Patagonia and elsewhere. Proglacial lakes can affect glacier dynamics, catchment hydrology and have the potential to cause glacial lake outburst floods. Therefore, monitoring the onset and development of proglacial lake formation is relevant to understand glacial processes and anticipate glacier response to climate change. In this study, we integrate geomorphological and ice-dynamic information to assess proglacial lake development in Exploradores Glacier, Chilean Patagonia. We monitor recent spatial and temporal changes in the lower trunk of Exploradores Glacier (10 km2) to provide a 20-year observation record by combining eight uncrewed aerial vehicles (UAV) surveys between 2019 and 2020, with high-medium resolution satellite imagery (Rapid Eye and Landsat) between 2000 and 2018. We use feature tracking techniques, digital surface elevation model analysis and field data to create a multi-temporal scale (inter-annual and seasonal) and a multi-spatial (cm to km) data set. Our analysis shows that surface velocity overall trend has not changed over the last 20 years and that surface velocity near the terminus is significant (>10 m a−1). Moreover, an exceptional advance over moraine deposits was detected. We also found low downwasting rates (<0.5 m a−1) close to the glacier terminus which are attributed to sufficient ice flux and the insulation effect of the debris-covered surface. However, hundreds of supraglacial ponds were observed and are currently coalescing and expanding by ice-cliff backwasting favoring glacier disintegration. Lastly, it was found that calving losses at the east marginal lake equaled ice-flux input into the lake for the UAV monitored period. This study contributes to a better understanding of glacial lake dynamics during proglacial lake development, and our results may help ice modelling efforts to predict glacier response to future climate scenarios.

Hydrologic variability in black ash wetlands: Implications for vulnerability to emerald ash borer

AbstractBlack ash (Fraxinus nigra) wetlands are widespread, forested landscape features in the western Great Lakes region. However, the future of these ecosystems is threatened due to impending spread of the invasive emerald ash borer (EAB), which results in tree mortality, decreased transpiration, and potential shifts to wetter, non‐forested conditions. The vulnerability to such ecohydrologic shifts likely varies according to local hydrologic regimes controlled by landscape settings, but this site‐dependent vulnerability and our ability to predict it is unknown. Here, we assessed vulnerability potential as a function of site hydrology in 15 undisturbed black ash wetlands from their three most common hydrogeomorphic settings in northern Minnesota: lowland, depression, and transition. Further, we used high‐resolution (1‐cm) surface elevation models to assess spatial variability of water levels at a subset of 10 sites. Although we observed similar ET and groundwater exchange rates among settings, lowland sites were generally drier because of elevated landscape position and greater water level drawdowns (via lower specific yield). We predict that such drier sites will exhibit greater water level increases following EAB‐induced ash mortality, compared to wetter sites where open water evaporation and shallow‐rooted understory transpiration will offset losses in tree transpiration. Moreover, compared to wetter sites, drier sites exhibited minimal microtopographic variation, limiting the number of elevated microsites for tree establishment and eventual canopy recovery after ash loss. These results suggest that site wetness is a simple and effective predictor of black ash wetland vulnerability to hydrologic regime change. To that end, we assessed the ability of common terrain metrics to predict site wetness, providing a potential tool to target vulnerable areas for active management efforts.

Accuracy assessment of late winter snow depth mapping for tundra environments using Structure-from-Motion photogrammetry

Arctic tundra environments are characterized by a spatially heterogeneous end-of-winter snow depth resulting from wind transport and deposition. Traditional methods for measuring snow depth do not accurately capture such heterogeneity at catchment scales. In this study we address the use of high-resolution, spatially distributed, snow depth data for Arctic environments through the application of unmanned aerial systems (UASs). We apply Structure-from-Motion photogrammetry to images collected using a fixed-wing UAS to produce a 1 m resolution snow depth product across seven areas of interest (AOIs) within the Trail Valley Creek Research Watershed, Northwest Territories, Canada. We evaluated these snow depth products with in situ measurements of both the snow surface elevation (n = 8434) and snow depth (n = 7191). When all AOIs were averaged, the RMSE of the snow surface elevation models was 0.16 m (<0.01 m bias), similar to the snow depth product (UASSD) RMSE of 0.15 m (+0.04 m bias). The distribution of snow depth between in situ measurements and UASSD was similar along the transects where in situ snow depth was collected, although similarity varies by AOI. Finally, we provide a discussion of factors that may influence the accuracy of the snow depth products including vegetation, environmental conditions, and study design.

Leveraging historical aerial photographs and digital photogrammetry techniques for landslide investigation—a practical perspective

Aerial photography has been extensively used for civil engineering applications for more than a century. The availability of digital photogrammetry tools has allowed for aircraft, UAV, and ground-based digital photogrammetry to become a reliable and standard tool for landslide management. Digital photographs and digitized historic aerial photos can be used to develop digital surface elevation models. This technical note presents a recent example of the use of historical aerial photographs in combination with modern remote sensing techniques and digital photogrammetry tools. The note provides valuable insights into landslide kinematics and evolution of the Chin Coulee landslide in southern Alberta, Canada. Conventional aerial photo interpretation allowed for a qualitative understanding of landslide feature evolution as a response to external factors (road construction and reservoir infilling at the toe of the landslide). More importantly, topographic changes were quantified through change detection techniques between topographic surfaces derived from historical photographs and a ground-based laser scanner. The results from change detection allowed to confirm the kinematics of the Chin Coulee landslide as a compound slide, an assumption which was previously based on limited deformation measurements. Furthermore, the results helped define the boundary between the active wedge of the landslide moving downslope as it pushes the passive wedge into the reservoir. Although challenges remain regarding the aggregation of datasets with different resolutions, this note demonstrates the valid practical application of this approach for landslide assessment and management.

Unmanned Aerial Systems (UAS)-Based Methods for Solar Induced Chlorophyll Fluorescence (SIF) Retrieval with Non-Imaging Spectrometers: State of the Art

Chlorophyll fluorescence (ChlF) information offers a deep insight into the plant physiological status by reason of the close relationship it has with the photosynthetic activity. The unmanned aerial systems (UAS)-based assessment of solar induced ChlF (SIF) using non-imaging spectrometers and radiance-based retrieval methods, has the potential to provide spatio-temporal photosynthetic performance information at field scale. The objective of this manuscript is to report the main advances in the development of UAS-based methods for SIF retrieval with non-imaging spectrometers through the latest scientific contributions, some of which are being developed within the frame of the Training on Remote Sensing for Ecosystem Modelling (TRuStEE) program. Investigations from the Universities of Edinburgh (School of Geosciences) and Tasmania (School of Technology, Environments and Design) are first presented, both sharing the principle of the spectroradiometer optical path bifurcation throughout, the so called ‘Piccolo-Doppio’ and ‘AirSIF’ systems, respectively. Furthermore, JB Hyperspectral Devices’ ongoing investigations towards the closest possible characterization of the atmospheric interference suffered by orbital platforms are outlined. The latest approach focuses on the observation of one single ground point across a multiple-kilometer atmosphere vertical column using the high altitude UAS named as AirFloX, mounted on a specifically designed and manufactured fixed wing platform: ‘FloXPlane’. We present technical details and preliminary results obtained from each instrument, a summary of their main characteristics, and finally the remaining challenges and open research questions are addressed. On the basis of the presented findings, the consensus is that SIF can be retrieved from low altitude spectroscopy. However, the UAS-based methods for SIF retrieval still present uncertainties associated with the current sensor characteristics and the spatio-temporal mismatching between aerial and ground measurements, which complicate robust validations. Complementary studies regarding the standardization of calibration methods and the characterization of spectroradiometers and data processing workflows are also required. Moreover, other open research questions such as those related to the implementation of atmospheric correction, bidirectional reflectance distribution function (BRDF) correction, and accurate surface elevation models remain to be addressed.

Mapping deep peat carbon stock from a LiDAR based DTM and field measurements, with application to eastern Sumatra

BackgroundReduction of carbon emissions from peatlands is recognized as an important factor in global climate change mitigation. Within the SE Asia region, areas of deeper peat present the greatest carbon stocks, and therefore the greatest potential for future carbon emissions from degradation and fire. They also support most of the remaining lowland swamp forest and its associated biodiversity. Accurate maps of deep peat are central to providing correct estimates of peat carbon stocks and to facilitating appropriate management interventions. We present a rapid and cost-effective approach to peat thickness mapping in raised peat bogs that applies a model of peat bottom elevation based on field measurements subtracted from a surface elevation model created from airborne LiDAR data.ResultsIn two raised peat bog test areas in Indonesia, we find that field peat thickness measurements correlate well with surface elevation derived from airborne LiDAR based DTMs (R2 0.83–0.88), confirming that the peat bottom is often relatively flat. On this basis, we created a map of extent and depth of deep peat (> 3 m) from a new DTM that covers two-thirds of Sumatran peatlands, applying a flat peat bottom of 0.61 m +MSL determined from the average of 2446 field measurements. A deep peat area coverage of 2.6 Mha or 60.1% of the total peat area in eastern Sumatra is mapped, suggesting that deep peat in this region is more common than shallow peat and its extent was underestimated in earlier maps. The associated deep peat carbon stock range is 9.0–11.5 Pg C in eastern Sumatra alone.ConclusionWe discuss how the deep peat map may be used to identify priority areas for peat and forest conservation and thereby help prevent major potential future carbon emissions and support the safeguarding of the remaining forest and biodiversity. We propose rapid application of this method to other coastal raised bog peatland areas in SE Asia in support of improved peatland zoning and management. We demonstrate that the upcoming global ICESat-2 and GEDI satellite LiDAR coverage will likely result in a global DTM that, within a few years, will be sufficiently accurate for this application.

Microtopography is a fundamental organizing structure of vegetation and soil chemistry in black ash wetlands

Abstract. All wetland ecosystems are controlled by water table and soil saturation dynamics, so any local-scale deviation in soil elevation and thus water table position represents variability in this primary control. Wetland microtopography is the structured variability in soil elevation and is typically categorized into a binary classification of local high points (hummocks) and local low points (hollows). Although the influence of microtopography on vegetation composition and biogeochemical processes in wetlands has received attention around the globe, its role in forested wetlands is still less understood. We studied relationships among microtopography and understory vegetation communities, tree biomass, and soil chemistry in 10 black ash (Fraxinus nigra Marshall) wetlands in northern Minnesota, USA. To do so, we combined a 1 cm resolution surface elevation model generated from terrestrial laser scanning (TLS) with colocated water table, vegetation, and soil measurements. We observed that microtopography was an important structural element across sites, where hummocks were loci of greater species richness; greater midstory and canopy basal area; and higher soil concentrations of chloride, phosphorus, and base cations. In contrast, hollows were associated with higher soil nitrate and sulfate concentrations. We also found that the effect of microtopography on vegetation and soils was greater at wetter sites than at drier sites, suggesting that the distance-to-mean water table is a primary determinant of wetland biogeochemistry. These findings highlight clear controls of microtopography on vegetation and soil distributions while also supporting the notion that microtopography arises from feedbacks that concentrate biomass, soil nutrients, and productivity on microsite highs, especially in otherwise wet conditions. We therefore conclude that microtopography is a fundamental organizing structure in black ash wetlands.

High‐throughput measurement of peanut canopy height using digital surface models

AbstractPeanut (Arachis hypogaea L.) is an important food and oilseed crop in the United States and worldwide with high net returns. However, input costs are high (US$1,970–$2,220 ha−1), and yield in excess of 4,500 kg ha−1 is needed to offset the costs. Since yield is limited by biotic and abiotic stresses, newer cultivars with tolerance to these stresses are needed to optimize yield. Plant height and canopy architecture may affect crop water use and plant disease resistance. However, measuring canopy height is a time‐consuming process. Surface elevation models from red–green–blue (RGB) aerial images have been successfully developed to estimate genetic differences of plant height for tall crops like corn (Zea mays L.) and sorghum [Sorghum bicolor (L) Moench]; but they have not been tested for short crops like peanut with a runner growth habit and much smaller height differences among genotypes. The objective of this study was to derive canopy height of peanut from digital surface models (DSM). Images were aerially taken using a digital camera mounted on an unmanned aerial vehicle (UAV). Images were orthomosaiced to create the DSM and the digital terrain model (DTM) of the plot. Canopy height was derived by subtracting the DTM from the DSM in ArcGIS software. Results showed that the RGB derived canopy height was highly correlated to the manually measured height (R2 = .953). We propose the methods used here as fast and relatively easy selection tools for breeders and crop growth evaluators of peanut plant height.

High-Resolution Representation for Mobile Mapping Data in Curved Regular Grid Model.

As mobile mapping systems become a mature technology, there are many applications for the process of the measured data. One interesting application is the use of driving simulators that can be used to analyze the data of tire vibration or vehicle simulations. In previous research, we presented our proposed method that can create a precise three-dimensional point cloud model of road surface regions and trajectory points. Our data sets were obtained by a vehicle-mounted mobile mapping system (MMS). The collected data were converted into point cloud data and color images. In this paper, we utilize the previous results as input data and present a solution that can generate an elevation grid for building an OpenCRG model. The OpenCRG project was originally developed to describe road surface elevation data, and also defined an open file format. As it can be difficult to generate a regular grid from point cloud directly, the road surface is first divided into straight lines, circular arcs, and and clothoids. Secondly, a non-regular grid which contains the elevation of road surface points is created for each road surface segment. Then, a regular grid is generated by accurately interpolating the elevation values from the non-regular grid. Finally, the curved regular grid (CRG) model files are created based on the above procedures, and can be visualized by OpenCRG tools. The experimental results on real-world data show that the proposed approach provided a very-high-resolution road surface elevation model.

A spatial model of streaked horned lark breeding habitat in the Columbia River, USA

The streaked horned lark (hereafter “lark”; Eremophila alpestris strigata) is a federally listed bird subspecies of the Pacific Northwest that occupies open landscapes with short vegetation and abundant bare ground. Across its breeding range, which has contracted dramatically, the lark relies primarily on human-modified habitats maintained in early successional states (e.g., agricultural fields, airfields, deposition islands). The focus of our study is the lower Columbia River where larks primarily occupy deposition islands created as a byproduct of shipping channel deepening (dredging) projects. The U.S. Army Corps of Engineers has proactively adopted a shifting-habitat-mosaic management approach when placing dredge (sand) materials to maintain lark habitat throughout the project area. To help achieve their goal, we created a geospatial tool capable of quantifying and tracking habitat suitability for larks throughout the project area with satellite imagery. We created spatial models of lark breeding habitat by incorporating lark survey data, Sentinel-2 satellite imagery, dredge-deposition maps, and surface-elevation models. We built candidate predictive models of lark breeding habitat after combining survey data (years 2016 and 2017), predictor variables, and logistic regression. In addition, we created a novel seral-stage predictor variable to identify young, mature, old, and unsuitable locations; critical information for lark conservation planning and dredge-disposal operational planning. We challenged probability models the year they were constructed (2016) and the following year (2017) with set-aside survey data. The best model contained terrain ruggedness, deposition age, vegetation greenness (e.g., lushness and density of vegetation) inside a 10-m cell, and heterogeneity in greenness within a 100-m radius. Verification accuracy ranged from 75 to 83% depending on the model tested and year. Importantly, the seral-stage variable allowed us to quantify and locate early, optimal, and late habitats. Model results will facilitate conservation planning decisions by informing real-time management decisions. Furthermore, they provide a foundation for application in other human-modified habitats across the species’ range.

Comparison of Surface Water Volume Estimation Methodologies That Couple Surface Reflectance Data and Digital Terrain Models

Uncertainty about global change requires alternatives to quantify the availability of water resources and their dynamics. A methodology based on different satellite imagery and surface elevation models to estimate surface water volumes would be useful to monitor flood events and reservoir storages. In this study, reservoirs with associated digital terrain models (DTM) and continuously monitored volumes were selected. The inundated extent was based on a supervised classification using surface reflectance in Landsat 5 images. To estimate associated water volumes, the DTMs were sampled at the perimeter of inundated areas and an inverse distance weighting interpolation was used to populate the water elevation inside the flooded polygons. The developed methodology (IDW) was compared against different published methodologies to estimate water volumes from digital elevation models, which assume either a flat water surface using the maximum elevation of inundated areas (Max), and a flat water surface using the median elevation of the perimeter of inundated areas (Median), or a tilted surface, where water elevations are based on an iterative focal maximum statistic with increasing window sizes (FwDET), and finally a tilted water surface obtained by replacing the focal maximum statistic from the FwDET methodology with a focal mean statistic (FwDET_mean). Volume estimates depend strongly on both water detection and the terrain model. The Max and the FwDET methodologies are highly affected by the water detection step, and the FwDET_mean methodology leads to lower volume estimates due to the iterative smoothing of elevations, which also tends to be computationally expensive for big areas. The Median and IDW methodologies outperform the rest of the methods, and IDW can be used for both reservoir and flood volume monitoring. Different sources of error can be observed, being systematic errors associated with the DTM acquisition time and the reported volumes, which for example fail to consider dynamic sedimentation processes taking place in reservoirs. Resolution effects account for a fraction of errors, being mainly caused by terrain curvature.

Assessing patterns of annual change to permafrost bluffs along the North Slope coast of Alaska using high-resolution imagery and elevation models

Coastal permafrost bluffs at Barter Island, on the North Slope, Beaufort Sea Coast of Alaska are among the most rapidly eroding along Alaska's coast, having retreated up to 132 m between 1955 and 2015. Here we quantify rates and patterns of change over a single year using very-high resolution orthophotomosaics and co-registered surface elevation models derived from a survey-grade form of structure-from-motion photogrammetry from a fixed-wing, manned aircraft. The resulting elevation models were validated with over 10,000 ground check points and found that 95% agreed to within 20 cm, before accounting for real differences in the ground surface due to seasonality, vegetation, and checkpoint acquisition errors. This data set provides the most detailed and accurate measurements of coastal change to date along the Alaskan coast and the method is scalable to more extensive coastlines. Between July 2014 and July 2015, the bluffs retreated an average of 1.3 m, and a maximum of 8.1 m, with an associated net volume loss of 38,100 ± 300 m3 (1.3 m3/m). This average retreat over this single year was slightly less than the 60-year mean rate of change of −1.5 ± 0.1 m/yr, suggesting the 2014–2015 year represented relatively typical to slightly below average conditions. Most of the bluff material (70%) was lost during the 3 summer months (July to Sept) of 2014 and the remaining 30% between the late-summer and following winter-spring. The pattern of change was predominantly landward retreat of the top of the bluffs, removal of the debris apron and subsequent niching at the base of the bluffs during mid to late summer (July to Sept) followed by erosion of the bluff face and deposition of debris at the base of the bluff through the remainder of the year (Sept to the following July). Drivers of the observed change are likely a combination of thermal erosion on the bluff face throughout the summer and episodic thermo-mechanical removal of material, niching, and undercutting of the base associated with high-water levels driven by low-pressure storms and westerly winds. These patterns and high rates of change are believed to be broadly representative of coastal permafrost bluffs found along many high-latitude coastlines worldwide.