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Several global digital elevation models (DEMs) have been developed in the last two decades. The most recent addition to the family of global DEMs is the TanDEM-X DEM. The original version of the TanDEM-X DEM is, however, a nonedited product (i.e., it contains local artefacts such as voids, spikes, and holes). Therefore, subsequent identification of local artefacts and their editing is necessary. In this study, we evaluated the accuracy of the original TanDEM-X DEM and its improved edited version, the Copernicus DEM, in three major European mountain ranges (the Alps, the Carpathians, and the Pyrenees) using a digital surface model derived from airborne laser scanning data as a reference. In addition, to evaluate the applicability of data acquisition characteristics (coverage map, consistency mask, and height error map) and terrain characteristics (slope, aspect, altitude) to the localization of problematic sites, we modeled their associations with the TanDEM-X DEM error. We revealed local occurrences of large errors in the TanDEM-X DEM that were typically found on steep ridges or in canyons, which were largely corrected in the Copernicus DEM. The editing procedure used for the Copernicus DEM construction was evidently successful as the RMSE for the TanDEM-X and Copernicus DEMs at the 90 m resolution improved from 45 m to 12 m, from 16 m to 6 m, and from 24 m to 9 m for the Alps, the Pyrenees, and the Carpathians, respectively. The Copernicus DEM at the 30 m resolution performed similarly well. The boosted regression trees showed that acquisition characteristics provided as auxiliary data are useful for locating problematic sites and explained 28–50% of deviance of the absolute vertical error. The absolute vertical error was strongly related to the height error map. Finally, up to 26% of cells in the Copernicus DEM were filled using DEMs from different time periods and, hence, users performing multitemporal analysis or requiring data from a specific time period in the mountain environment should be wary when using TanDEM-X and its derivations. We suggest that when filling problematic sites using alternative DEMs, more attention should be paid to the period of their collection to minimize the temporal displacement in the final products.

At least 10 global digital elevation models (DEMs) at one-arc-second resolution now cover Earth. Comparing derived grids, like slope or curvature, preserves surface spatial relationships, and can be more important than just elevation values. Such comparisons provide more nuanced DEM rankings than just elevation root mean square error (RMSE) for a small number of points. We present three new comparison categories: fraction of unexplained variance (FUV) for grids with continuous floating point values; accuracy metrics for integer code raster classifications; and comparison of stream channel vector networks. We compare six global DEMs that are digital surface models (DSMs), and four edited versions that use machine learning/artificial intelligence techniques to create a bare-earth digital terrain model (DTM) for different elevation ranges: full Earth elevations, under 120 m, under 80 m, and under 10 m. We find edited DTMs improve on elevation values, but because they do not incorporate other metrics in their training they do not improve overall on the source Copernicus DSM. We also rank 17 common geomorphic-derived grids for sensitivity to DEM quality, and document how landscape characteristics, especially slope, affect the results. None of the DEMs perform well in areas with low average slope compared to reference DTMs aggregated from 1 m airborne lidar data. This indicates that accurate work in low-relief areas grappling with global climate change should use airborne lidar or very high resolution image-derived DTMs.

The open source 30 m Copernicus DEM (COP-DEM)   has been used to derive the geo-morphometric and topo-hydrological characteristics of Betwa River Basin. Drainage network with 7 th order stream and mostly dendritic pattern has been delineated using the Strahler's method. The drainage density, stream frequency, form factor, length of overland flow and circulatory ratio of the basin were computed as 0.38 Km/Km 2 , 0.08 Km −2 , 0.23, 1.31, and 0.20, respectively. These outcomes suggest less available surface flow, lesser relative relief, poor drainage network, and nearly elongated shape of the basin. The mean bifurcation ratio for entire basin was calculated as 4.0 that signifies gradient dependent drainage network of the basin. The ruggedness number was computed as 0.24, which reflects the geology dominated (granite-gneiss) rocky and undulated topography of the basin. The dissection index ranges from 0.06 to 0.3, which implies less degree of dissection and mature stage of the basin. The topographic wetness index (TWI), stream power index (SPI), terrain ruggedness index (TRI), and sediment transport index (STI) ranges from 3.13 to 26.35; 0 to 6; 0 to 30; and 0 to 121.4, respectively. It implies that the lower basin is less susceptible towards erosion as compared to upper basin.

What are the main findings? * Digital elevation models with one-arc-second are still the best free scale available globally. When compared to a lidar-derived reference digital terrain model, FathomDEM consistently performs best but has a restrictive license. The Copernicus DEM is the best free option, with the ALOS AW3D30 only in rugged and steep mountainous areas. We also evaluated FABDEM and GEDTM v1.2. * The capability of global DEM to represent land surface parameters, such as slope, curvatures, and roughness changes in relation to land cover and morphology. Parameters computed with the second order partial derivatives show a range of correspondence, and those computed with third order partial derivatives show extremely low correspondence. Digital elevation models with one-arc-second are still the best free scale available globally. When compared to a lidar-derived reference digital terrain model, FathomDEM consistently performs best but has a restrictive license. The Copernicus DEM is the best free option, with the ALOS AW3D30 only in rugged and steep mountainous areas. We also evaluated FABDEM and GEDTM v1.2. The capability of global DEM to represent land surface parameters, such as slope, curvatures, and roughness changes in relation to land cover and morphology. Parameters computed with the second order partial derivatives show a range of correspondence, and those computed with third order partial derivatives show extremely low correspondence. What is the implication of the main finding? * The procedures for creating a bare earth digital elevation from a digital surface model are a black box that can hallucinate, and the results must be checked carefully. The creators should check derived land surface parameters as well as the raw elevation values, as a good digital surface model can be better than a poor digital terrain model. * Geomorphometry workers must carefully assess the land surface parameters they use. First derivative parameters perform best; second derivative parameters, like curvature, vary in their signal-to-noise ratio; the third derivative parameters, like change of curvature, might be all noise. The procedures for creating a bare earth digital elevation from a digital surface model are a black box that can hallucinate, and the results must be checked carefully. The creators should check derived land surface parameters as well as the raw elevation values, as a good digital surface model can be better than a poor digital terrain model. Geomorphometry workers must carefully assess the land surface parameters they use. First derivative parameters perform best; second derivative parameters, like curvature, vary in their signal-to-noise ratio; the third derivative parameters, like change of curvature, might be all noise. We evaluated six global digital elevation DEMs at 1-arc-sec resolution: CopDEM and AW3D30, which are digital surface models (DSMs), and EDTM, GEDTM, FABDEM, and FathomDEM, which are digital terrain models (DTMs). We compared them to reference DTMs created by mean aggregation from 1–2 m lidar-derived DTMs from national mapping agencies, using 1510 approximately 10 × 10 km test tiles from the United States and western Europe. Our criteria used the grids for elevation and derived land surface parameters (LSPs), including characteristics of the difference distributions and the fraction unexplained variance derived from grid correlations. The best DEM depends on the LSP used and the characteristics of the test tile, especially average slope, barrenness, and forest coverage. FathomDEM emerged as the best among the DEMs, with CopDEM the best overall for the DEMs with unrestricted licenses. GEDTM performed poorly. This is especially important for LSPs like curvature measures, which require higher-order partial derivatives for computation, and which should be used very cautiously.

Flood hazard and risk analysis in developing countries is a difficult task due to the absence or scarce availability of flow data and digital elevation models (DEMs) with the necessary quality. Up to eight DEMs (ALOS Palsar, Aster GDEM, Bare Earth DEM, SRTM DEM, Merit DEM, TanDEM-X DEM, NASA DEM, and Copernicus DEM) of different data acquisition, spatial resolution, and data processing were used to reconstruct the January 2015 flood event. The systematic flow rate record from the Mocuba city gauge station as well as international aid organisms and field data were used to define both the return period peak flows in years for different flood frequencies (Tyear) and the January 2015 flooding event peak flow. Both visual and statistical analysis of flow depth values at control point locations give us a measure of the different hydraulic modelling performance. The results related to the Copernicus DEM, both in visual and statistical approach, show a clear improvement over the results of the other free global DEMs. Under the assumption that Copernicus DEM provides the best results, a flood hazard analysis was carried out, its results being in agreement with previous data of the effects of the January 2015 flooding event in the Mocuba District. All these results highlight the step forward that Copernicus DEM represents for flood hazard analysis in developing countries, along with the use of so-called “citizen science” in the form of flooding evidence field data acquisition.

The availability of global digital elevation models (DEMs) from multiple time points allows their combination for analysing vegetation changes. The combination of models (e.g., SRTM and TanDEM-X) can contain errors, which can, due to their synergistic effects, yield incorrect results. We used a high-resolution LiDAR-derived digital surface model (DSM) to evaluate the accuracy of canopy height estimates of the aforementioned global DEMs. In addition, we subtracted SRTM and TanDEM-X data at 90 and 30 m resolutions, respectively, to detect deforestation caused by bark beetle disturbance and evaluated the associations of their difference with terrain characteristics. The study areas covered three Central European mountain ranges and their surrounding areas: Bohemian Forest, Erzgebirge, and Giant Mountains. We found that vertical bias of SRTM and TanDEM-X, relative to the canopy height, is similar with negative values of up to −2.5 m and LE90s below 7.8 m in non-forest areas. In forests, the vertical bias of SRTM and TanDEM-X ranged from −0.5 to 4.1 m and LE90s from 7.2 to 11.0 m, respectively. The height differences between SRTM and TanDEM-X show moderate dependence on the slope and its orientation. LE90s for TDX-SRTM differences tended to be smaller for east-facing than for west-facing slopes, and varied, with aspect, by up to 1.5 m in non-forest areas and 3 m in forests, respectively. Finally, subtracting SRTM and NASA DEMs from TanDEM-X and Copernicus DEMs, respectively, successfully identified large areas of deforestation caused by hurricane Kyril in 2007 and a subsequent bark beetle disturbance in the Bohemian Forest. However, local errors in TanDEM-X, associated mainly with forest-covered west-facing slopes, resulted in erroneous identification of deforestation. Therefore, caution is needed when combining SRTM and TanDEM-X data in multitemporal studies in a mountain environment. Still, we can conclude that SRTM and TanDEM-X data represent suitable near global sources for the identification of deforestation in the period between the time points of their acquisition.

Tree decline is a highly complex process and is inherently a function of manifold climatic, physiologic, and anthropogenic factors. Monitoring decline processes and their underlying dynamics primarily entails identifying their location and intensity across different ecosystems, for which airborne and satellite remote sensing approaches offer cost-effective and spatially explicit alternatives to field methods. Consumer-grade unmanned aerial vehicles (UAVs) can barely be used as standalone means for large-area monitoring due to their constrains in spatial and spectral domains. However, they could effectively be integrated alongside satellite data to unlock their information for subsequent upscaling on landscape level. We designed a novel two-step workflow to describe the severity of tree decline by linking UAV-RGB information to space-borne multispectral and digital elevation model (DEM) data over 15 forest sites dominated by Persian oak across the latitudinal gradient of Zagros Forests in western Iran. We display how to 1) leverage UAV as reference data across multiple structurally different Persian oak-dominated sites in semi-arid Zagros mountains of Iran; 2) link UAV, Copernicus DEM, and Sentinel-2 data to retrieve decline information within a model-driven context; and 3) analyze the sensitivity of models by means of a global variance-based sensitivity analysis. Results suggested a high association between UAV and field data on the intensity of decline, which enabled using sampled UAV data as reference to estimate the decline severity using space-borne data by means of semi-parametric generalized additive model (GAM) and non-parametric random forest (RF) approaches. Conclusively, this study provided a baseline for multi-scale analysis of tree decline using budget and partially free data sources, which can be of high scientific and practical assets for monitoring in remote, sparse, mountainous, and continuously degrading forest areas.

Recent Digital Surface, Elevation, and Bathymetric Models (DSM/DEM/DBM) aim to provide high-resolution and accurate height and depth information needed for a variety of surveying, geodetic, geophysical, and other applications. In this study, first we aim to validate in two test areas some of the most used models, i.e., ASTER GDEM; AW3D30 DSM; Copernicus DEM; EU-DEM; GEBCO 2020; NASADEM HGT; SRTM15+ and SRTM Global, using GNSS; spirit leveling; and gravity measurements. The validation is performed along two traverses of 14.5 and 12.0 km each in Northern and Central Greece, respectively. Since these models are based on geoid heights obtained from global geopotential models, we also investigate their influence on the validation results. Next, we carry out comparisons between GEBCO 2020, SRTM15+, and the Greek Seas DTM, with depths derived from in situ coastal measurements in six different areas in Northern Greece. From the analysis, we conclude that the heights obtained from the Copernicus DEM provide the best overall results in terms of mean value and standard deviation while also showing consistent results in the two test areas. Similarly, the Greek Seas DTM shows better consistency with the measured depths in the coastal test areas.

Herausgegeben von Heribert M. Nobis, Menso Folkerts, Stefan Kirschner und Andreas Kühne Die neue, kritische und kommentierte Gesamtausgabe der Werke von Nicolaus Copernicus erscheint seit 1973. Das Editionsprojekt, ursprünglich während des Zweiten Weltkriegs gestartet, war in der Nachkriegszeit zum Erliegen gekommen. Nur die ersten beiden Bände dieser ersten Edition konnten erscheinen. Allerdings hinterließen die Copernicus-Forscher Franz und Karl Zeller sowie Hans Schmauch Vorarbeiten für weitere Bände, die der von der Deutschen Forschungsgemeinschaft ins Leben gerufenen Copernicus-Forschungsstelle zur Verfügung gestellt wurden. Seit 1989 befindet sich diese Forschungsstelle im Institut für Geschichte der Naturwissenschaften der Ludwig-Maximilians-Universität München. Herausgeber der Gesamtausgabe sind Heribert M. Nobis, Menso Folkerts, Stefan Kirschner und Andreas Kühne. In Zusammenarbeit mit der Copernicus-Forschungsstelle der Polnischen Akademie der Wissenschaften wurde in München ein zentrales Copernicus-Archiv aufgebaut. Zum Index zu Band II der Nicolaus Copernicus Gesamtausgabe (De revolutionibus. Libri sex. Kritischer Text. Besorgt von Heribert Maria Nobis und Bernhard Sticker. Hildesheim 1984) Zur Fakultät für Mathematik, Informatik und Naturwissenschaften der Universität Hamburg Zum Historischen Seminar der Ludwig Maximilians Universität München