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The global digital elevation model (DEM) is important for various scientific applications. With the recently released TanDEM-X 90-m DEM and AW3D30 version 2.2, the open global or near-global coverage DEM datasets have been further expanded. However, the quality of these DEMs has not yet been fully characterized, especially in the application for regional scale studies. In this study, we assess the quality of five freely available global DEM datasets (SRTM-1 DEM, SRTM-3 DEM, ASTER GDEM2, AW3D30 DEM and TanDEM-X 90-m DEM) and one 30-m resampled TanDEM-X DEM (hereafter called TDX30) over the south-central Chinese province of Hunan. Then, the newly-released high precision ICESat-2 (Ice, Cloud, and land Elevation Satellite-2) altimetry points are introduced to evaluate the accuracy of these DEMs. Results show that the SRTM1 DEM offers the best quality with a Root Mean Square Error (RMSE) of 8.0 m, and ASTER GDEM2 has the worst quality with the RMSE of 10.1 m. We also compared the vertical accuracies of these DEMs with respect to different terrain morphological characteristics (e.g., elevation, slope and aspect) and land cover types. It reveals that the DEM accuracy decreases when the terrain elevation and slope value increase, whereas no relationship was found between DEM error and terrain aspect. Furthermore, the results show that the accuracy increases as the land cover type changes from vegetated to non-vegetated. Overall, the SRTM1 DEM, with high spatial resolution and high vertical accuracy, is currently the most promising dataset among these DEMs and it could, therefore, be utilized for the studies and applications requiring accurate DEMs.

DEMs derived from Interferometric Synthetic Aperture Radar (InSAR) imagery are frequently influenced by multiple factors, resulting in systematic horizontal and elevation inaccuracies that affect their applicability in large-scale scenarios. To mitigate this problem, this study employs affine models and polynomial function models to refine the relative planar precision and elevation accuracy of the DEM. To acquire high-quality control data for the adjustment model, this study introduces a DEM feature matching method that maintains invariance to geometric distortions, utilizing filtered ICESat-2 ATL08 data as elevation control to enhance accuracy. We first validate the effectiveness and features of the proposed InSAR-DEM matching algorithm and select 45 ALOS high-resolution DEM scenes with different terrain features for large-scale DEM block adjustment experiments. Additionally, we select additional Sentinel-1 and Copernicus DEM data to verify the reliability of multi-source DEM matching and adjustment. The experimental results indicate that elevation errors across different study areas were reduced by approximately 50% to 5%, while the relative planar accuracy improved by around 93% to 17%. The TPs extraction method for InSAR-DEM proposed in this paper is more accurate at the sub-pixel level compared to traditional sliding window matching methods and is more robust in the case of non-uniform geometric deformations.

The Beas sub basin falling under the Indus basin in Northern India is experiencing notable changes due to human interventions since the rise of civilization in the Indus valley. The incessant anthropogenic pressure, infrastructural development, deforestation and encroachment have made the sub basin more vulnerable to land degradation, erosion and landslides. Thus this study attempts to classify the watersheds based on morphometric characteristics and prioritize the watersheds for sub basin management as a whole so that restoration process can concentrate on the high risk prone watersheds. In this study ALOS PALSAR DEM of 12.5 meters was used to extract the drainage network, watershed, catchment sub basin and basin boundary complemented by topographic and hydrological maps. The study analyses 49 morphometric parameters under categories like linear, areal and relief characteristics. The result classifies the erosion capacity of total 4126 streams with the cumulative length of 12,287.51 km over a sub basin area of 19,338.8 Km2. The morphometric parameters were integrated for each watershed and compound factor was given to rank vulnerability in the GIS environment. The results depicted that sub watershed numbers 2, 6, 12, 16 were high risk prone and underlined as an area which requires immediate attention for soil water conservation measures.

This study proposes a streamlined workflow for producing historical digital elevation models (hDEMs) from scanned 1950s aerial photographs using structure-from-motion and multi-view-stereo (SfM-MVS) techniques along with co-registration methods. We also conducted a sensitivity analysis to assess the impact of DEM references with varying spatial resolutions on the SfM-MVS process and co-registration accuracy. The DEM references included a 30 m SRTM DEM (low resolution), a 12 m TanDEM-X DEM (medium resolution), and a 5 m DEM provided by the General Directorate of Mapping of the Ministry of National Defense, Republic of Türkiye (high resolution). Results indicate that higher resolution reference DEMs lead to improved accuracy and precision of the final hDEMs, particularly evident in reduced errors and finer spatial resolution. This study contributes to streamlining the hDEM construction process and offers a nuanced understanding of the significance of elevation and reference DEM selection in ensuring hDEM accuracy.

Magmatic continental rifts often constitute nascent plate boundaries, yet long‐term extension rates and transient rate changes associated with these early stages of continental breakup remain difficult to determine. Here, we derive a time‐averaged minimum extension rate for the inner graben of the Northern Kenya Rift (NKR) of the East African Rift System for the last 0.5 m.y. We use the TanDEM‐X science digital elevation model to evaluate fault‐scarp geometries and determine fault throws across the volcano‐tectonic axis of the inner graben of the NKR. Along rift‐perpendicular profiles, amounts of cumulative extension are determined, and by integrating four new 40Ar/39Ar radiometric dates for the Silali volcano into the existing geochronology of the faulted volcanic units, time‐averaged extension rates are calculated. This study reveals that in the inner graben of the NKR, the long‐term extension rate based on mid‐Pleistocene to recent brittle deformation has minimum values of 1.0–1.6 mm yr−1, locally with values up to 2.0 mm yr−1. A comparison with the decadal, geodetically determined extension rate reveals that at least 65% of the extension must be accommodated within a narrow, 20‐km‐wide zone of the inner rift. In light of virtually inactive border faults of the NKR, we show that extension is focused in the region of the active volcano‐tectonic axis in the inner graben, thus highlighting the maturing of continental rifting in the NKR. Plain Language Summary When two of the world's tectonic plates slowly move apart, a rift valley forms, which will form a divergent plate boundary. After millions of years of spreading, such a rift valley can become an ocean basin, but at first, the valley is still part of the continent, and the landscape has steep steps and volcanoes. The Kenya Rift in East Africa is such an opening plate boundary in its early form. However, it is difficult to find out how fast the opening has been on long timescales. With the help of a digital elevation model and a specialized computer code, we measure the heights of the topographic steps inside the Northern Kenya Rift valley. We also took rock samples to determine the age of the volcanoes and their lava flows. These two pieces of information can be put together: We calculate an average speed of the extension of the Northern Kenya Rift. We found out that during the last half million years, the Kenya Rift has opened at least about 1.6 mm each year. This movement happens mostly in the center of the rift valley. The flanks of the Kenya Rift valley are currently not affected. Key Points In the inner graben of the Northern Kenya Rift valley, normal fault scarp heights have been mapped using the 12‐m‐resolution TanDEM‐X DEM The minimum long‐term extension rate at this plate boundary is between 1.0 and 1.6 mm yr−1 since the middle Pleistocene Extension is focused in the volcano‐tectonic axis of the rift while older border faults show virtually no activity in the last 0.5 m.y

Satellite digital elevation models (DEMs) are used for decision-making in various fields. Therefore, evaluating and improving vertical accuracy of DEM can increase the quality of end products. This article aimed to increase the vertical accuracy of most popular satellite DEMs (i.e., the ASTER, Shuttle Radar Topography Mission [SRTM], Forest And Buildings removed Copernicus DEM [FABDEM], and Multi-Error-Removed Improved-Terrain [MERIT]) using the particle swarm optimization (PSO) algorithm. For this purpose, at first, the vertical error of DEMs was estimated via ground truth data. Next, a second-order polynomial was applied to model the vertical error in the study area. To select the polynomial with the highest accuracy, employed for vertical error modeling, the coefficients of the polynomial have been optimized using the PSO algorithm. Finally, the efficiency of the proposed algorithm has been evaluated by other ground truth data and observations. The results show that the mean absolute error (MAE) of SRTM DEM is 4.83 m while this factor for ASTER DEM is 5.35 m, for FABDEM is 4.28, and for MERIT is 3.87. The obtained results indicated that the proposed model could improve the MAE of vertical accuracy of SRTM, ASTER, FABDEM, and MERIT DEMs to 0.83, 0.51, 0.37, and 0.29 m, respectively.

Rotating discs are usually used as granulators in many industrial processes. The efficiency of the granulation process in this device is directly related to the particle motion behavior in different flow regimes. In this work, the granular flow in a rotating disc was investigated experimentally and numerically. The Discrete Element Method (DEM) was used in the simulations, while Central Composite Designs (CCD) were employed to quantify the effects of DEM input parameters and operating conditions (filling degree (FD), angle of inclination (AI), and rotational speed) on the contacts between particles. The results showed that the particle–wall static friction coefficient had the most significant impact on the studied response. Additionally, the effect of operating variables on the collision force between particles, the angle of departure and particle velocities was successfully investigated, with corresponding DEM simulation predictions. It was also verified that the simulations performed with experimentally measured DEM input parameter values were able to reproduce the flow regimes in the rotating disc.

Devastating floods are observed every year globally from upstream mountainous to coastal regions. Increasing flood frequency and impacts affect both major rivers and their tributaries. Nonetheless, at the small-scale, the lack of distributed topographic and hydrologic data determines tributaries to be often missing in inundation modeling and mapping studies. Advances in Unmanned Aerial Vehicle (UAV) technologies and Digital Elevation Models (DEM)-based hydrologic modeling can address this crucial knowledge gap. UAVs provide very high resolution and accurate DEMs with low surveying cost and time, as compared to DEMs obtained by Light Detection and Ranging (LiDAR), satellite, or GPS field campaigns. In this work, we selected a LiDAR DEM as a benchmark for comparing the performances of a UAV and a nation-scale high-resolution DEM (TINITALY) in representing floodplain topography for flood simulations. The different DEMs were processed to provide inputs to a hydrologic-hydraulic modeling chain, including the DEM-based EBA4SUB (Event-Based Approach for Small and Ungauged Basins) hydrologic modeling framework for design hydrograph estimation in ungauged basins; the 2D hydraulic model FLO-2D for flood wave routing and hazard mapping. The results of this research provided quantitative analyses, demonstrating the consistent performances of the UAV-derived DEM in supporting affordable distributed flood extension and depth simulations.

Based on discrete element method (DEM) simulations, this study investigates the formation of granular jets triggered by the sudden unloading of a compressed granular column. After unloading, a jet can be generated from a granular column with a meniscus-shaped free surface. The evolution of jet velocity can be divided into two stages: the acceleration stage and the gravity-governed stage. In the gravity-governed stage, a grain stream can exhibit different regimes, including dispersed atomized grains, a sharp tip, and an elongated root. The effects of the key physical properties of grains on the jet velocity in the early stage are investigated. We find that a higher Young’s Modulus is beneficial for generating a granular jet. The sliding friction coefficient and the coefficient of restitution have limited effects, which implies that the jet velocity is insensitive to the damping and tangential forces of the grains. Mass density significantly influences the velocity of granular jets. It is found that the jet velocity is proportional to the natural frequency of the grain-spring system. An increase in cohesion energy density leads to a reduction in jet velocity.

Discrete Element Method (DEM) was proposed by Cundall and Strack (1979) and gained traction in the field of powder engineering during the late 1980s. In the 1990s, various applications of DEM were conducted in the powder technology field, and the capability of DEM for predicting powder behavior was acknowledged. In the 2000s and 2010s, advancements in computing technology and the availability of general-purpose software led to the widespread adoption of numerical simulation as a prevalent tool in industrial applications. The authors have been engaged in discrete particle modeling of gas–solid two-phase flows and the development of DEM–CFD models for the numerical analysis of both dense gas–solid two-phase flows and gas–liquid–solid three-phase flows. Thus, this paper aims to provide a comprehensive description of the pioneering development of discrete particle models and simulations conducted by the authors.