LiDAR Topographic Data Research Articles

Parallel Topology-aware Mesh Simplification on Terrain Trees

We address the problem of performing a topology-aware simplification algorithm on a compact and distributed data structure for triangle meshes, the Terrain trees. Topology-aware operators have been defined to coarsen a Triangulated Irregular Network (TIN) without affecting the topology of its underlying terrain, i.e., without modifying critical features of the terrain, such as pits, saddles, peaks, and their connectivity. However, their scalability is limited for large-scale meshes. Our proposed algorithm uses a batched processing strategy to reduce both the memory and time requirements of the simplification process, and thanks to the spatial decomposition on the basis of Terrain trees, it can be easily parallelized. Also, since a Terrain tree after the simplification process becomes less compact and efficient, we propose an efficient post-processing step for updating hierarchical spatial decomposition. Our experiments on real-world TINs, derived from topographic and bathymetric LiDAR data, demonstrate the scalability and efficiency of our approach. Specifically, topology-aware simplification on Terrain trees uses 40% less memory and half the time compared to the most compact and efficient connectivity-based data structure for TINs. Furthermore, the parallel simplification algorithm on the Terrain trees exhibits a 12× speedup with an OpenMP implementation. The quality of the output mesh is not significantly affected by the distributed and parallel simplification strategy of Terrain trees, and we obtain similar quality levels compared to the global baseline method.

Controls on the morphological evolution of embayed beaches: Morphometry versus external forcing

AbstractThe morphological evolution of embayed beaches on a microtidal coast is assumed to largely respond to the degree of exposure to wave conditions, decreasing the mobility with increasing beach indentation (and vice versa). However, the number of sediment arrivals at the beach or the impact of extreme storms can modify this relationship. Here, we present an analysis of 10 embayed beaches along the Catalan coast with different morphometric and sedimentary characteristics to identify the most relevant parameters controlling the morphological evolution of these embayed beaches at the inter‐annual and decadal scales. The study was mostly based on LiDAR topographic data collected from 2012 to 2017, aerial photographs from 1945 to 2021, sediment sampling and a long‐term series analysis of the forcing parameters (waves, sea level, precipitation and land‐use changes). The results show a net loss of volume on all the studied beaches at an inter‐annual scale and a general shoreline retreat during the last few decades, suggesting the influence of common processes on the evolution of the studied beaches. Smaller pocket beaches with medium‐to‐high indentations are more sensitive to changes induced by local factors and show higher variability in the volume of the emerged beach and shoreline position than larger beaches. The most relevant factors influencing the evolution of the studied beaches on a decadal scale were identified as changes in sea level and the reduction in sediment inputs provided by streams due to land‐use changes in the drainage basin. At the inter‐annual scale, the impact of extreme events is the main factor controlling beach behaviour. These general trends can be opposite locally for beaches that receive large amounts of sediment via longshore transport from adjacent beaches.

The expected impacts of sea level on the Mexican Atlantic coast

The Mexican Atlantic coast is vulnerable to sea level rise due to its low, sandy shorelines with extensive adjacent wetlands. The increasing trends at the regional level are similar to global trends (~3 ± 0.04 mm/year): between 1.8 mm/year in Alvarado, Veracruz, to 3.6 mm/year in Isla Mujeres, Quintana Roo. A synthetic model was applied to Mexican Atlantic coast under two sea level rise scenarios for the year 2100. Our objectives were: 1) to identify potentially floodable zones in the face of a sea level rise of one and two meters on the Mexican Atlantic coast with a synthetic model using SRTM and LiDAR topographic data; 2) to determine vegetation and land use affected in the potentially floodable zones; and 3) quantify the vulnerable human population. With topographic data we identified low areas (one and two meters) to assess potentially floodable zones; these were intersected with data layers of vegetation, land use, and human population. Deltaic zones, coastal lagoons and low-lying areas of the Yucatan Peninsula were regions with the largest potentially floodable surface. In the one-meter sea rise scenario, 581,674 ha were identified as potentially floodable, and 896,151 in the two-meter scenario. The most vulnerable vegetation and land use types were wetlands, such as cattail marshes (tulares; ~29 %) and mangroves (~27 %), as well as cultivated grasslands (~6 %). The indirectly affected coastal population could be approximately 5.5 million in these scenarios (~33 %), and the directly affected population could range between 124,000 and 440,000 (~0.72 and 2.55 %, respectively). These results indicate that there will be strong effects in economic, social, and environmental impacts on the Atlantic coast of Mexico in the event of a one- and two-meters sea level rise. This type of work will enable proposal conservation and adaptation strategies for human populations and coastal cities.

Automated fluvial hydromorphology mapping from airborne remote sensing

AbstractMapping fluvial hydromorphology is an important part of defining river habitat. Mapping via field sampling or hydraulic modeling is however time consuming, and mapping hydromorphology directly from remote sensing data may offer an efficient solution. Here, we present a system for automated classification of fluvial hydromorphology based on a deep learning classification scheme applied to aerial orthophotos. Using selected rivers in Norway, we show how surface flow patterns (smooth or rippled surfaces vs. standing waves) can be classified in imagery using a trained convolutional neural network (achieving a training and validation accuracy of >95%). We show how integration of these classified surface flow patterns with information on channel gradient, obtained from airborne topographic LiDAR data, can be used to compartmentalize the rivers into hydromorphological units (HMUs) that represent the dominant flow features. Automated classifications were broadly consistent with manual classifications that had been made in previous ground surveys, with equivalency in automated and manually derived HMU classes ranging from 61.5% to 87.7%, depending on the river stretch considered. They were found to be discharge‐dependent, showing the temporally dynamic aspect of hydromorphology. The proposed system is quick, flexible, generalizable, and provides consistent classifications free from interpretation bias. The deep learning approach used here can be customized to provide more detailed information on flow features, such as delineating between standing waves and advective diffusion of air bubbles/foam, to provide a more refined classification of surface flow patterns, and the classification approach can be further advanced by inclusion of additional remote sensing methods that provide further information on hydromorphological features.

Testing the potential of drowned shore platforms as sea level proxies in a temperate, microtidal environment: Victoria, Australia

Shore platforms are erosional benches, often found at the base sea cliffs, which form through erosion concentrated within the intertidal zone. In locations without suitable depositional proxies, these erosional landforms have been used to reconstruct past sea levels. The precision and accuracy of shore platforms as sea level proxies is highly variable as their morphology, particularly their vertical position in the intertidal zone, is modulated by boundary conditions especially those related to the geology in which they are formed. In this study the semi-horizontal shore platforms on the microtidal temperate coast of Victoria, Australia are examined to test the utility of these systems as sea level indicators. These results are then applied to a suite of submerged shore platforms found offshore using high-resolution LiDAR topographic and multi-beam sonar bathymetric data. The elevation of both the contemporary and drowned platforms are measured at both the cliff-platform junction and the mid-point of each profile line. Both methods are compared to assess their utility to represent sea level at the time of their formation. It is found that those platforms formed within resistant sandstone and basalt are the best proxies for sea level forming in the upper intertidal zone, while those formed in softer Tertiary carbonates are less precise being predominately subtidal features. The morphology of the drowned platforms is broadly similar to those at current sea level elevations, and they are concentrated at a depth 49.7 to 57.2 m below modern sea level. It is inferred that these drowned platforms likely formed during marine isotope stage 5a or 5d.

Interpolation of airborne LiDAR data for archaeology

The use of topographic airborne LiDAR data has become an essential part of archaeological prospection, and the need for an archaeology-specific data processing workflow is well established. However, interpolation, an important step in which the digital elevation model is derived from the classified point cloud, has received little attention from archaeologists. This processing step has a direct impact on the accuracy and visual performance of the digital elevation model, but remains a challenge despite numerous studies. Most studies have compared the accuracy of different interpolators (with conflicting results), but very few compare the visual performance. Also, there are no archaeology-specific studies. This article addresses this problem by providing an archaeology-specific visual performance assessment of six of the most commonly used interpolators. The data was tested at four European test sites with innovative use of the triangular assessment method. Kriging was the best interpolator in undersampled areas, and inverse distance weighting was a distant second. In other areas, triangulation with linear interpolation was marginally better than kriging. However, when availability and computational costs are also taken into account, inverse distance weighting is currently the most suitable archaeology-specific interpolator. In addition, we propose a hybrid interpolator that combines the strengths of triangulation with linear interpolation and inverse distance weighting (QGIS plug-in). All results are to be considered European-data specific.

Natural remobilization and historical evolution of a modern coastal transgressive dunefield

AbstractThe vast majority of coastal dunes in Europe have been stabilized by increasing vegetation cover since the mid‐20th century. However, some systems may experience a remobilization phase, generally occurring locally and further propagating alongshore, the drivers of which remain poorly documented. This study investigates the evolutionary paths (stabilization/destabilization/remobilization) from 1945 to 2020 of a 2 km‐long modern coastal transgressive dunefield located in southwest France with a holistic approach (GPR profiles, aerial photographs and LiDAR topographic data). Results show a landward migration of the transgressive dune by approximately 233 ± 7.5 m, through two distinct stages of rapid landward migration from 10 to 23 m/yr (Stage I: 1949–1959 and Stage III: 2000–2021) separated by an approximately 40‐year stage of slow to no migration, but with substantial windward slope deflation (Stage II). The onset of Stage II is due to the fixation of vegetation by human action between 1950 and 1959. The onset of Stage III is hypothesized to be driven by long and sustained upper backshore/dune toe erosion beginning in 1968 due to a massive shoal welding that locally disturbed the longshore drift. It induced a destabilization of the dune and erosion of the vegetation cover over some decades. A non‐synchronization is therefore observed between the start of the perturbation (1968), then the migration (2000), in line with the hysteresis concept of Tsoar (2005). This study shows that almost all of the sedimentary volume of the 1945 dune has been remobilized by translation to shape the dune system in its current form. The 2.2 km dunefield has grown by approximately 673 000 ± 190 000 m3 during the 2005–2020 period. Among this volume, there is a new foredune that was built from 2005 between the upper beach and the transgressive dune (volume in 2020 of about 394 000 ± 68 000 m3).

Long-term sediment storage and flux in a small, catastrophically aggraded mountain catchment

A discrete period of hydraulic gold mining in the northwestern Sierra Nevada, California (1853–1884) and extreme channel aggradation provide an opportunity to examine long-term catchment-scale sediment transport. This study used high-resolution LiDAR topographic data to reconstruct historical surfaces and compute spatially distributed sediment budgets in Greenhorn Creek, a small (42-km2) unregulated mountainous catchment. Digital elevation models (DEMs) were constructed for three periods: pre-mining (ca.1853), maximum aggradation (ca.1884), and modern (2013–14). Differencing DEMs enabled computation of changes in sediment volume between dates, and computation of sediment production, storage, and flux. Hydraulic mines in upper Greenhorn Creek produced 41 × 106 m3 of sediment, of which 16 × 106 m3 (38%) and 4.8 × 106 m3 (12%) were stored by 1884 and 2014, respectively. Mining-sediment fluxes were high compared to global sediment-yield databases averaging 33,042 t km−2yr−1 (1853–1884) and 3845 t km−2yr−1 (1884–2014). Catchment denudation rates computed from mine-pit volumes ranged from one to four orders of magnitude greater than background. Valley-bottom mining-sediment storage decreased through time but remained substantial 130 years after mining ceased. Storage in 2014 occurred mostly in the lower catchment except for substantial storage in two cut-off valley bends. Many studies compute or model sediment delivery ratios as an inherent property of basin size or physiography that can be used to route sediment, but how do sediment delivery ratios change through time? A hypothesis that post-mining sediment delivery ratios were at least 10% greater during the mining period was not rejected. Results support a dynamic sediment-delivery ratio concept in which the proportion of sediment delivered increases through time following a discrete sediment pulse. Large sediment-production events can leave lasting legacies that should be recognized by river managers.

Comparison between Topographic and Bathymetric LiDAR Terrain Models in Flood Inundation Estimations

Remotely sensed LiDAR data has allowed for more accurate flood map generation through hydraulic simulations. Topographic and bathymetric LiDARs are the two types of LiDAR used, of which the former cannot penetrate water bodies while the latter can. Usually, the topographic LiDAR is more available than bathymetric LiDAR, and it is, therefore, a very interesting data source for flood mapping. In this study, we made comparisons between flood inundation maps from several flood scenarios generated by the HEC-RAS 2D model for 11 sites in Norway using both bathymetric and topographic terrain models. The main objective is to investigate the accuracy of the flood inundations generated from the plain topographic LiDAR, the links of the inaccuracies with geomorphic features, and the potential of using corrections for missing underwater geometry in the topographic LiDAR data to improve accuracy. The results show that the difference in inundation between topographic and bathymetric LiDAR models decreases with increasing the flood size, and this trend was found to be correlated with the amount of protection embankments in the reach. In reaches where considerable embankments are constructed, the difference between the inundations increases until the embankments are overtopped and then returns to the general trend. In addition, the magnitude of the inundation error was found to correlate positively with the sinuosity and embankment coverage and negatively with the angle of the bank. Corrections were conducted by modifying the flood discharge based on the flight discharge of the topographic LiDAR or by correcting the topographic LiDAR terrain based on the volume of the flight discharge, where the latter method generally gave better improvements.

Sedimentology of a hypertidal point bar (Mont‐Saint‐Michel Bay, north‐western France) revealed by combining lidar time‐series and sedimentary core data

AbstractIntertidal meanders developed on salt marshes are known to expand and produce inclined heterolithic stratification rich in fine‐grained sediments and to bear evidence for rhythmic deposition in the upper part of the inner meander bend (i.e. the upper part of the point bar). This occurs because the lower point‐bar deposits are washed by strong currents, which remove mud drapes and develop discontinuous record of tidal cycles. Although these criteria are widely accepted, facies models for tidal point bars still lack a three‐dimensional perspective and overlook the along‐bend variability of sediment distribution. The present study focuses on a hypertidal point bar belonging to the upper‐intertidal domain of the Mont‐Saint‐Michel Bay (France), and it analyses the sedimentology of a 3D time‐framed accretionary package formed between 28 March 2012 and 29 November 2012 by means of lidar topographic data, geomorphological field surveys and sedimentological core data. To define the 3D time‐framed accretionary package, data from thirteen lidar (light detection and ranging) topographic surveys were used to create the point‐bar synthetic stratigraphy. Data show that over the study period the point bar expanded alternating deposition along its seaward and landward sides, pointing out the occurrence of depositional patterns more complex than a simple progressive expansion of the bend. The thickest deposits were accumulated in the point‐bar‐apex zone, where the largest amount of mud was also stored. High sediment accretion in the bend‐apex zone is ascribed to the development of low‐energy conditions due to flow and bed configuration. High accretion rate of the point‐bar‐apex zone promoted also a better preservation of rhythmites, which are almost missing from deposits accumulated along the point‐bar sides. This study remarks that preservation of mud and tidal rhythmites within intertidal‐point‐bar deposits is controlled, not only by their elevation with respect to the tidal range, but also by their location along the point bar.

Late to post-Variscan basement segmentation and differential exhumation along the SW Bohemian Massif, central Europe

Abstract. The exposed Variscan basement in central Europe is well-known for its complex structural and lithological architecture resulting from multiple deformation phases. We studied the southwestern margin of the Bohemian Massif, which is characterized by major and long-lived shear zones, such as the Pfahl and Danube shear zones, extending over > 100 km and initiated during Variscan tectonics. We integrated Bouguer gravity anomaly and lidar topographic data analyses and combined our results with available data and observations from low-temperature thermochronology, metamorphic grades, and the exposed granite inventory to detect patterns of basement block segmentation and differential exhumation. Three NW–SE-striking basement blocks are bordered by the Runding, Pfahl, and Danube shear zones from the northeast to the southwest. Basement block boundaries are indicated by abrupt changes in measured gravity patterns and metamorphic grades. By applying high-pass filters to gravity data in combination with lineament analysis, we identified a new NNW–SSE-striking tectonic structure (Cham Fault), which further segments known basement blocks. Basement blocks that are segmented by the Cham Fault differ in the abundance and spatial distribution of exposed late Variscan granites and are further characterized by variations in apparent thermochronological age data. Based on our observations and analyses, a differential exhumation and tectonic tilt model is proposed to explain the juxtaposition of different crustal levels. Block segmentation along the NW–SE-striking Pfahl and Runding shear zones most likely occurred prior, during, and after late orogenic granite emplacement at ca. 320 ± 10 Ma, as some of the granites are cross-cut by the shear zones, while others utilized these structures during magma ascent and emplacement. In contrast, activity and block segmentation along the Cham Fault occurred after granite emplacement as the fault sharply truncates the granite inventory. Our study provides evidence of intense and continuous fault activities during late and post-orogenic times and highlights the importance of tectonic structures in the exhumation and juxtaposition of different crustal levels and the creation of complex lithological patterns in orogenic terrains.

Application of Airborne LiDAR Data to the Archaeology of Agrarian Land Use: The Case Study of the Early Medieval Microregion of Bled (Slovenia)

The use of topographic airborne LiDAR data has become an essential part of archaeological prospection, particularly as a tool for detecting archaeological features in the landscape. However, its use for landscape reconstruction and understanding archaeological sites in their environmental context is still underutilised. To this end, we took an innovative approach to using LiDAR data as a means of discovering, documenting, and interpreting agricultural land use systems by looking for significant environmental variation within a microregion. We combined information from LiDAR-derived DEM derivatives with archaeological, geological, and soil data. We introduced two methodological innovations. The first is the modified wetness index, which combines the LiDAR-derived precision with the accuracy of the effective field capacity of the soil to obtain a very realistic predictor of soil quality. The second is the modified landform classification, a combination of topographic position index and visual geomorphological analysis, which amalgamates two of the most important predictive variables for the distribution of plant species. Our approach is demonstrated by a case study focusing on early medieval settlements in the context of agricultural land use in the subalpine microregion of Bled (Slovenia). It revealed that early medieval settlers were drawn to light soils with high water retention capacity. Such soils were particularly suitable for the cultivation of barley, which is known to have been one of the most important staple crops of the period, especially in colder climate such as subalpine. Soils with lower water retention capacity were not colonized until the eleventh century, which may signify the transition at that time to a higher level of agricultural organisation and wheat as a staple cereal food.

Airborne LiDAR Point Cloud Processing for Archaeology. Pipeline and QGIS Toolbox

The use of topographic airborne LiDAR data has become an essential part of archaeological prospection. However, as a step towards theoretically aware, impactful, and reproducible research, a more rigorous and transparent method of data processing is required. To this end, we set out to create a processing pipeline for archaeology-specific point cloud processing and derivation of products that are optimized for general-purpose data. The proposed pipeline improves on ground and building point cloud classification. The main area of innovation in the proposed pipeline is raster grid interpolation. We have improved the state-of-the-art by introducing a hybrid interpolation technique that combines inverse distance weighting with a triangulated irregular network with linear interpolation. State-of-the-art solutions for enhanced visualizations are included and essential metadata and paradata are also generated. In addition, we have introduced a QGIS plug-in that implements the pipeline as a one-step process. It reduces the manual workload by 75 to 90 percent and requires no special skills other than a general familiarity with the QGIS environment. It is intended that the pipeline and tool will contribute to the white-boxing of archaeology-specific airborne LiDAR data processing. In discussion, the role of data processing in the knowledge production process is explored.

Exploring new methods to analyse spatial impact distributions on debris‐flow fans using data from south‐western British Columbia

AbstractPredicting the spatial impact of debris flows on fans is challenging due to complex runout behaviour. Debris flow mobility is highly variable and flows can sporadically avulse the channel. For hazard and risk assessments, practitioners typically base the probability of spatial impact or avulsion on their experience and expert judgement. To support decision‐making with empirical observations, we studied spatial impact distributions on 30 active debris‐flow fans in south‐western British Columbia, Canada. We mapped 146 debris‐flow impact areas over an average observation period of 74 years using orthorectified airphotos, satellite imagery, topographic base maps, LiDAR data, orthophotos, and field observations. We devised a graphical method to convert our geospatial mapping into spatial impact heat maps normalized by fan boundaries, enabling comparison of runout distributions across different fans. About 90% of the mapped debris flows reached beyond the mid‐points of fans, while less than 10% avulsed more than half‐way across the fan relative to the previous flow path. Most avulsions initiated at distances of 20% to 40% of the maximum fan length from the fan apex and upstream of the fan intersection point. Large volume events tend to be more mobile in the down‐fan direction, but the relation between volume and cross‐fan runout (e.g., avulsions) is more complex. Differences in spatial impact distributions can be explained, in part, by the degree of fan incision and whether a fan is truncated at its toe by a river or lake. There were no significant differences in spatial impact distributions based on the geology of the source area, sediment supply condition, or hydrogeomorphic process classification.

Airborne LiDAR-Derived Digital Elevation Model for Archaeology

The use of topographic airborne LiDAR data has become an essential part of archaeological prospection, and the need for an archaeology-specific data processing workflow is well known. It is therefore surprising that little attention has been paid to the key element of processing: an archaeology-specific DEM. Accordingly, the aim of this paper is to describe an archaeology-specific DEM in detail, provide a tool for its automatic precision assessment, and determine the appropriate grid resolution. We define an archaeology-specific DEM as a subtype of DEM, which is interpolated from ground points, buildings, and four morphological types of archaeological features. We introduce a confidence map (QGIS plug-in) that assigns a confidence level to each grid cell. This is primarily used to attach a confidence level to each archaeological feature, which is useful for detecting data bias in archaeological interpretation. Confidence mapping is also an effective tool for identifying the optimal grid resolution for specific datasets. Beyond archaeological applications, the confidence map provides clear criteria for segmentation, which is one of the unsolved problems of DEM interpolation. All of these are important steps towards the general methodological maturity of airborne LiDAR in archaeology, which is our ultimate goal.

Assessment of Future Flood Hazards for Southeastern Texas: Synthesizing Subsidence, Sea‐Level Rise, and Storm Surge Scenarios

AbstractRecent hurricanes highlight shortcomings of flood resilience plans in Texas that can worsen with climate change and rising seas. Combining vertical land motion (VLM) with sea‐level rise (SLR) projections and storm surge scenarios for the years 2030, 2050, and 2100, we quantify the extent of flooding hazards. VLM rates are obtained from GNSS data and InSAR imagery from ALOS and Sentinel‐1A/B satellites. VLM is resampled and projected on LIDAR topographic data, then multiple inundation and flooding scenarios are modeled. By the year 2100, over 76 km2 are projected to subside below sea level. Subsidence increases the area of inundation over SLR alone by up to 39%. Under the worst‐case composite scenario of an 8‐m storm surge, subsidence, and the SLR RCP8.5, the total affected area is 1,156 km2. These models enable communities to improve flood resiliency plans.

Geology and Aquifer Sensitivity of Quaternary Glacial Deposits Overlying a Portion of the Mahomet Buried Bedrock Valley Aquifer System

To characterize the distribution of Holocene and Late Quaternary deposits and to assess the contamination potential of the Mahomet Aquifer, surficial geologic and aquifer sensitivity maps of the Gibson City East 7.5-Minute Quadrangle were created. Geologic data, extent, and thickness of the geologic materials were coupled with LiDAR topographic data and analyzed using ESRI’s ArcGIS 10.6.1. Aquifer sensitivity to contamination was calculated based on the depth to the first aquifer unit, aquifer thickness, and the lithology of the aquifer materials. The surficial geologic mapping identified five lithostratigraphic units: the Cahokia Formation, the Equality Formation, the Henry Formation, and the Yorkville and Batestown Members of the Lemont Formation. The southeast to northwest trending Illiana Morainic System is the most prominent feature in the study area and delineates the maximum extent of the glaciers during the Livingston Phase of glaciation. Postglacial deposits of the Cahokia Formation, alluvium, interfinger, and overlie with glacial outwash of the Henry Formation along channels and drainage ways downslope of the moraine. The areas of least sensitivity are located over the Illiana Morainic System, whereas the greatest potential to contamination occurs where the thickest deposits of the Henry Formation and Cahokia Formation lie at or just below the land surface.

A Method to Derive Bathymetry for Dynamic Water Bodies Using ICESat-2 and GSWD Data Sets

Detailed information on lake bathymetry is essential for both hydrology-related studies and water resource management. Conventionally, lake bathymetry was mapped using high-cost approaches (e.g., ship/boat-based multibeam echosounders or airborne bathymetric lidars). With only satellite remotely sensed data sets, a method for deriving high-resolution bathymetry for dynamic areas was proposed by combining the new Ice, Cloud, and land Elevation Satellite-2 (ICESat-2) lidar data and the Landsat-based Global Surface Water Data Set (GSWD). First, ICESat-2 can provide accurate along-track topographic points after the point cloud processing and bathymetric error correction, and the GSWD can supply water occurrence information within the lake dynamic area between 1984 and 2018. Second, using the derived relationship between the elevation and water occurrence, the bathymetric map of Lake Mead, USA, was produced with the dynamic area exceeding 235 km <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , elevation ranging nearly 37 m, and a resolution of 30 m. The local reference data (i.e., the airborne topographic lidar data and ship/boat-based bathymetric data) in six areas around Lake Mead were used for the validations. In general, the produced lake bathymetry achieved an accuracy of approximately 2 m in elevation with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$R^{2}$ </tex-math></inline-formula> of 0.97. The proposed method is promising to obtain global bathymetry for inland water bodies (e.g., the lake and reservoir) and coastal areas (e.g., the tidal zone) where water level fluctuations are strong and the water clarity is sufficient.

Spatial and Temporal Development of Incipient Dunes

AbstractIn zones of loose sand, wind‐blown sand dunes emerge due the linear instability of a flat sedimentary bed. This instability has been studied in experiments and numerical models but rarely in the field, due to the large time and length scales involved. We examine dune formation at the upwind margin of the White Sands Dune Field in New Mexico (USA), using 4 years of lidar topographic data to follow the spatial and temporal development of incipient dunes. Data quantify dune wavelength, growth rate, and propagation velocity and also the characteristic length scale associated with the growth process. We show that all these measurements are in quantitative agreement with predictions from linear stability analysis. This validation makes it possible to use the theory to reliably interpret dune‐pattern characteristics and provide quantitative constraints on associated wind regimes and sediment properties, where direct local measurements are not available or feasible.

Analysis of beach and foredune changes by aerial photography and topographic profiles, Tasmania, Australia

Beach foredunes following introduction of Ammophila arenaria have been shown to promote accretion and progradation, but after a few decades, large steep-faced foredunes develop that subsequently erode. Beach profile measurement combined with spatial change techniques have not been applied to investigation of A. arenaria foredune change before. This study investigated two adjacent beaches in Tasmania along 3.4km of coastline, one infested by A. arenaria and the other retaining native vegetation. Dune profile surveys were derived from topographic measurement and LiDAR data, and recent aerial imagery was analysed using the Digital Shoreline Analysis System to quantify net shoreline movement and rates of change. Results showed lack of progradation on the A. arenaria infested beach, with tall, steep-faced, concave foredunes that retreated up to 15m in 10 years. By contrast, the native vegetated beach showed continued progradation, with smaller convex-faced foredunes. The A. arenaria foredunes retreated particularly where the dune toe was lower in elevation. Sediment supply is likely reduced by the tall foredunes with dense vegetation-holding sand, causing storm erosion not to be replaced, hence a lowering beach and dune toe. Future erosion is likely to be a greater risk with sand supply locked into high volume A. arenaria-infested dunes, relative to native vegetated dunes.