Use Of Digital Elevation Models Research Articles

Positioning of a lunar surface rover on the south pole using LCNS and DEMs

With the renewed interest in the lunar surface exploration, the European Space Agency is supporting, as part of the Moonlight program, the development of a dedicated Lunar Communications and Navigation Service (LCNS) infrastructure. This should enable to achieve real time positioning and autonomous navigation in the cislunar space, including, among others, lunar landing and surface operations. One of the services proposed, as part of the LunaNet framework (NASA, 2022), is called the Lunar Augmented Navigation Service (LANS) and it is based on a GNSS-like concept. However, compared to Earth-based GNSS, the expected number of available satellites in lunar orbit will initially be limited, which triggers the interest of coupling these technologies at the receiver level with other navigation data sources. In the case of surface rovers, use of digital elevation model (DEM) data has shown to be a potential other source of information to support positioning. The purpose of this contribution is to look at the actual navigation performances achievable when using a simple (four satellites constellation) lunar radio navigation constellation combined with a DEM, through a state estimation filter, for different rover dynamic and different DEM accuracy levels. It is shown that a 5 meter real-time horizontal position accuracy can be achieved, for 99.7% of the time, using a precise enough DEM (5 m/pixel) and a 4 satellite-constellation under different rover’s dynamic conditions (i.e. velocities).

We Prefer to Stay Grounded!

We have proposed a three-pronged approach to identify sustainable practices during road construction: (1) Route segmentation and identification of drive phases, including loading and dumping stages; (2) Use of Digital Elevation Models (DEM) and digital terrain models(DTM) acquired by UAVs to measure progress of construction from volumetric changes; and (3) Use of vegetation indices derived from satellite imagery to calculate changes in carbon stock. The paper introduces a novel technique for identifying driving phases for heavy trucks based only on GPS data. We also delve into how these approaches can serve as the foundational elements in the creation of digital twins tailored to the construction industry.

Improved estimation of the underestimated GEDI footprint LAI in dense forests

ABSTRACT Light Detection and Ranging (LiDAR), with its ability to capture vegetation vertical profile, could be a unique technique for deriving Leaf Area Index (LAI). A global LAI product at 25-m spatial resolution was derived from the Global Ecosystem Dynamics Investigation (GEDI) LiDAR data since 2019, but it was often significantly underestimated in dense forests. Here we explored the potential for improving the estimation of the underestimated GEDI LAI in dense forests by using the Digital Elevation Model (DEM) as auxiliary data to separate ground and canopy returns in the received waveform. Dense forests were defined as forests with high vegetation greenness (annual maximum NDVI ≥ 0.8). The newly estimated GEDI footprint LAI was first validated with the ground-measured LAI at two sites in Fujian, China, and the results showed that the underestimation was significantly reduced compared to the original GEDI LAI product (r increased from −0.55 to 0.81, RMSE decreased from 3.94 to 1.43, Bias decreased from 3.17 to 0.48). To evaluate whether the improvement was applicable to other areas and forest types, the newly estimated GEDI footprint LAI for the entire Fujian and Contiguous US (CONUS) was then compared to the consistent LAI among three widely used global LAI products. The comparison results demonstrated that the use of DEM as auxiliary data could largely reduce the underestimation of GEDI footprint LAI (In Fujian, RMSE decreased from 4.75 to 2.52, and Bias decreased from 4.61 to 0.58; in CONUS, RMSE decreased from 5.24 to 1.96, and Bias decreased from 5.1 to 0.73). Overall, this study demonstrates the effectiveness of correcting the large underestimation of GEDI footprint LAI in dense forests by utilizing DEM, which has an important influence on the results, as auxiliary data.

COST-EFFICIENT METHODS OF DERIVING SLOPE INFORMATION FOR ROAD SEGMENTS IN DRIVER-ASSISTANCE APPLICATIONS

Abstract. An advanced driver-assistance system (ADAS) is any of a group of technologies that assist drivers in driving and parking functions. Through a safe human-machine interface, ADAS increase car and road safety. These Advanced driver-assistance systems rely on special maps with extended geometry and attribute information. This extra information includes slope, curvature, and speed limit. ADAS-enabled maps are usually rather expensive in the industry. This paper is focused on finding cost-efficient alternatives for generating the slope aspect of ADAS maps. Slope and height information is not only used in ADAS but is a critical aspect of calculating electronic vehicle (EV) ranges, and truck fuel-efficiency calculations as well. ADAS slope information usually requires high-accuracy surveys. This paper researches the possible generation of slope information for road segments with the use of digital elevation models (DEM) or crowdsourcing with low-cost sensors and Kalman filtering. The first approach is based on globally available DEMs with interpolation and filtering with road geometry. DEMs have variable accuracy depending on the type of technology used in producing them. Such technologies include photogrammetry, aerial and terrestrial laser scanning (ALS, TLS), or aerial or space radar measurements. The other method is by using low-cost GPS and IMU sensors for generating altitude profiles. These produced altitude profiles are compared with a profile generated from a high-accuracy survey using large-resolution DEMs produced by aerial photogrammetry or aerial laser scanning. This paper proposes metrics with which these datasets can be compared, one is using the height differences, and the other compares the slope values at discrete common points. In the conclusion, the paper tries to find use cases for the low-accuracy data.

Analisis Spasial Kenaikan Tinggi Permukaan Air Batang Sumani Menggunakan Model Permukaan Digital

The occurrence of flooding in the Batang Sumani area of ​​Solok Regency is caused by several things, including the low slope of the river, the river cross-section which is not wide enough, the topography of the plains, heavy bends along the river and silting due to sedimentation and the vulnerability to flood hazards which is quite high in the watershed area. The influence of the topography of the plains causes inundation on land managed and used by the community. In accordance with technological developments in digital mapping of the earth's surface, the earth's surface can be presented in the form of a three-dimensional map called a Digital Elevation Model (DEM). This DEM is used as a model, analysis and representation of conditions related to the earth's surface. The use of DEM in the process of analyzing inundation caused by surface runoff will help in identifying the coverage of inundation areas and water catchment areas. By using the Simulate water level rise / flooding analysis from the Global Mapper application it is possible to simulate water level rise / flooding which makes it possible to simulate the coverage or spread of water/flooding by increasing the water level to a certain depth and spatial analysis using the Geographic Information System can see the influence of the inundation area on land use managed by the community around the inundation area. So that the location and coverage of the inundation on land use can be obtained. Most of the inundation areas are in garden areas at 37.56%, rice fields at 23.83%, fields at 24.03% and residential areas at 13.67%. There was a significant increase in the water level rise of 2 meters.

Use of Digital Elevation Models in Metallogenic Investigations on the Example of the Central Part of the Lower Amur Province

Abstract —The digital elevation model (SRTM03) of the central part of the Lower Amur province is analyzed. The Limuri–Amgun ring structure is identified on the basis of a set of features, and it is also the location of the Pilda–Limuri and Kherpuchin–V’yunsky gold-ore regions, as well as the Albazino deposit, known for large industrial gold deposits and many small deposits and ore occurrences. The distribution of linear and ring elements of the relief is analyzed and geologically interpreted, and its spatial relationship with gold deposits and ore occurrences is shown. The relationship between the morphological severity of the ring structure and the deep structure of the region is shown. It is revealed that the structure is magmatic and characterized by a high concentration of intrusive bodies. According to the reference data on the age and composition of the igneous complexes of the region, the formation of the ring structure is associated with the processes of formation and transformation of the Earth’s crust and upper mantle during the end of the Late Cretaceous and the onset of the Paleocene in a suprasubduction geodynamic setting.

Using Texture Statistics to Identify and Map Different Dune Types within the Rub’ al Khali

Understanding the movement, direction, and shape of sand dunes can contribute to reducing their impact on infrastructure and the environment. The Rub’ al Khali desert has a distribution of dune types. This study aims to identify and map the different types of dunes within the Rub’ al Khali using a texture analysis method based on a digital elevation model (DEM). Statistical texture analysis methods (variance, skewness, and kurtosis) show three different textures of sand dune shapes, according to the geography of the dunes, using data contained in global DEMs. The analysis presented in this study focused on the use of DEMs to investigate the varied dune morphology within the Rub’ al Khali. The GMTED2010 and EarthEnv_DEM90 digital elevation models were compared. Spatial variability in dune height, spatial variability in dune texture, and profile graphs were created to examine dune surfaces in cross-section. The results provided six different dune types within the sand sea: giant compound linear dunes, simple linear dunes, simple transverse dunes, compound crescentic dunes (megabarchans), huge star dunes, and many transitional forms that defy classification. The results showed that the compound linear dune and simple linear dune were the dominant dune types, covering 41.61% and 31.7% of the total study area, respectively. The maps of variance, using either 10 × 10 and 30 × 30 focal blocks, produced a fairly sharp distinction in dune texture. It is hoped that future research in aeolian geomorphology will greatly benefit from these results, which could easily be expanded with the use of more sophisticated pattern recognition software, which clearly shows the value of using such an approach.

Enhancing the Urban Atlas Features with the Water Balance Estimates Using the Landsat 8 Imagery

Between climate change and anthropogenic forcing, pressure on water resources is continually increasing all over the world. The growing population is gathering more and more in cities where the artificialization of soils and urban developments of all kinds are modifying the local water cycle. However, knowledge about the hydrological cycle in urban areas is not well developed today. Urbanization in a watershed can produce significant changes to the natural water cycle, mainly because permeable soils have been covered by less permeable surfaces. The consequences of this urbanization can be significant and multiple. The assessment of urban water resources aims to provide a suitable circumstances for planning, conditions for the planning, design, construction, operation, and maintenance of works used for irrigation and sanitation, among other applications. The methodology of the research is based on the data collection, which includes climatic data from June 2021 to June 2022 and the use of Digital elevation model to create a hydrographic network. The second part is land use data processing to create a land cover map using maximum Likelihood Supervised Classification, by combining different band composites of Landsat 8 images and NDVI to differentiate between vegetative and non-vegetative areas. However, CORINE Land Cover database was utilized to distinguish between continuous and discontinuous urban area in this classification. The final step in the process is to determine the hydrological coefficients by calculating the water cycle parameters (Evapotranspiration Runoff and Infiltration) for each land-use class. Furthermore, establishing a link between land use and hydrological behaviour and conducting a precise calculation of water balance-related coefficients in urban areas using Urban Atlas 2018.

The use of digital elevation model and GIS for geometric analysis of water reservoir to feed the hypothetical irrigation project west Makhoul in Salahuddin province

The reservoir under study is one of the basic components of the supposedly irrigation project, the geometric analysis of the reservoir was conducted, the geometric elements were extracted from the DEM, which are represented by the positive volume (the volume of islands), negative volume (volume of water storage), positive planner area (the projections of islands), negative planner area (area of evaporation), positive surface area (undulated surface of islands), negative surface area (bottom wetted area), average thickness of islands and the average of depth, at selected levels of the reservoir, the relations between geometric elements and water level, and geometric elements with each other, reveal that the positive volume and positive areas typically fluctuated with the changes of water level, because the immersion of islands and emergence of new other islands with the rising of levels, these elements are important for the future uses for these positive areas, as well as in the future maintain within the reservoir, and the way of movement between parts, and possible problems due to landslides from the positive parts towards the negative ones.
 The negative volume and negative areas are very important in the operational policy of the reservoir, which are a positive not fluctuated relationships, the negative volume, negative planar and surface areas increased with the beginning of the level rising as low sharpness, then the sharpness of these relationships increased because of the relatively large increase of these elements after the departure of reserve from the original stream of Al-Jafr valley to its shoulders.
 The study also showed that the topography of the bottom and the islands are not significantly complicated, that facilitating the use of the area for tourism purposes and the construction of other parts of the irrigation project.
 According to the derived geometric elements from the digital elevation model, mathematical model were developed for predicting the water levels which are achieved inside the reservoir in terms of water volume that is pumped into the reservoir, that have great significance in the operational program for the project.
 The study reflect that the supposed reservoir may contain twirled reserve of water enough for up to 20 days of continuous pumping to the main channel with average pumping 50 m3/s, the operator can control the volume of storage by the operational program which is subject to the variation of demand in the main and secondary channels.

Analysis of Meanders and Bends of Lesser Zab River from Dalga VViilllage to Darbandi Rania

This study investigates the meanders of the Lesser Zab River in the study area, in terms of morphometric characteristics such as )length, width, direction, shape, area and symmetry of the meanders( and their distribution along the main river in the river valley through explaining the forcing factors in the creation of such shapes such as slope, geological structure, transported materials, flow of tributaries into the main river and tectonic activity in terms of geomorphic actions such as (carving, removal, transportation and sedimentation(, with the influence of human factors. Also, the phases of meanders development from north to south in the river valley are discussed. Furthermore, differences and dissimilarities of such formation can be seen between the periods 1972-2021; this is reflected in morphometric characteristics and geomorphic actions in all parts of the river basin. This research relies on various research methods such as deductive method, numerical methods and cartographic methods; using (ArcGIS.version.10.8), with the use of digital elevation model (DEM12.5m), to conduct detailed field work by the researcher. In the study area, 17 bends and meanders in the river have been identified, of which 7 bends were bends and 10 were meandering with the percent of meandering reaching (1.58), and the bend of Kewiya has the highest rate of twist, which reached (5.4). At the same time, the value of symmetry in the bend of Bekhre village is completely symmetric, because the value of each side (X) and (Y) is 49. For example, the length of the river for each of the years (2020,1984 and 2021) consecutively reached (32 km, 32.876 km, 31.7٢7 km), These changes will affect the size of human activities in the study area such as )distribution of human settlements, agricultural activities, poultry farms, fish ponds and industrial activities).

Volumetric Obscurance as a New Tool to Better Visualize Relief from Digital Elevation Models

The use of digital elevation models (DEMs) has become much more widespread in recent years, thanks to technological developments that facilitate their creation and availability. To exploit these data, a set of processing techniques has been developed to reveal the characteristic structures of the relief. This paper presents a new method based on the volumetric approach, and two derivatives. These methods are evaluated on three DEMs at different resolutions and scales: a freely accessible DEM from JAXA DEM covering part of North-East Tanzania, a DEM corresponding to rock art in Siberia, and a DEM of an archaeological Bronze Age funeral structure. Our results show that with the volumetric approach, concave and convex areas are clearly visible, with contrast marking slope breaks, while the overall relief is attenuated. Furthermore, the use of volume reduces the impact of noise, which can occur when processing is based on sky visibility (e.g., sky-view factor or positive openness) or second derivatives. Finally, the volumetric approach allows the implementation of a vertical exaggeration factor, the result of which will enhance the particular characteristics of the landscape. The present study comes with a standalone executable program for Windows, a QGIS plugin, and the scripts written in Python, including GPU compute capability (via CUDA) for faster processing.

MICRONUTRIENT DYNAMICS IN RELATION TO SOIL PROPERTIES IN ARABLE SOILS OF RIGACHIKUN-KADUNA, NORTHERN GUINEA SAVANNAH, NIGERIA

The research was conducted within January 2020 – January 2021 at the arable soils of Rigachikun-Kaduna, Northern Guinea Savanna and intended to study the micronutrient dynamics and relationships with some studied soil properties. Previously harvested maize, cowpea and rice soils (designated as Locations A, B and C respectively) were delineated, and three profile pits dug in each along the line of transect of about 100 m apart. A total of nine profile pits were dug in the three delineations and samples collected from each pit according to their horizonations. The use of Digital Elevation Model (DEM) was employed to study the terrain characteristics of the location. Major micronutrients investigated were Cu, Fe, Zn and Mn. Virtually all micronutrients decreased down the profile in all studied locations with Cu and Zn displaying an irregular trend in all pedons of rice harvested soils in location C. Also Fe rather increased in pedon 1 of location C as well. Cu had positive and non-significant correlation with other micronutrients (Fe and Zn), it however had a significant relationship with Mn. With respect to other soil properties investigated, Cu maintained a negative non-significant correlations. Fe had a positive and highly significant correlation with Mn and Zn. Also, Fe had a significant and negative correlation with organic matter but positive with available phosphorus. Fe was positively but non-significantly correlated with other soil properties such as clay, Ca, Mg, and total exchangeable bases (TEB). There was however, a non-significant and negative correlations of Fe with soil pH, K, Na as well as total exchangeable acidity (TEA). Mn only had significant and positive correlations with all other micronutrients (Cu, Fe and Zn) but non-significantly correlated with other soil properties. Micronutrients were all low to a deficiency level considering their critical limits in the tropical soils. Low organic matter content of soils of Rigachikun may have contributed to low micronutrient reserve of the soils. Activities that will conserve organic matter such as accumulation of litter from harvested crops and alternative means of cattle rearing such ranching rather than freelance grazing should be employed, as efforts to replenish micronutrients through fertilization has not yielded the desired results.

The first sub-meter resolution digital elevation model of the Kruger National Park, South Africa

The use of digital elevation models has proven to be crucial in numerous studies related to savanna ecosystem research. However, the insufficient spatial resolution of the chosen input data is often considered to be a limiting factor when conducting local to regional scale ecosystem analysis. The elevation models and orthorectified imagery created in this study represent the first wall-to-wall digital elevation data sets produced for the Kruger National Park (KNP), South Africa, at very high spatial resolution. Using colour-infrared (CIR) aerial imagery from the archives of the Chief Directorate: National Geo-spatial Information (CDNGI), Department of Agriculture, Land Reform and Rural Development (DALRRD) aerial acquisition programme, we created digital surface models (DSMs), digital terrain models (DTMs) and CIR orthomosaics covering the entire KNP with a nominal ground sampling distance of 0.25 m. Elevation information was derived using state-of-the-art stereo matching algorithms that utilised semi-global matching (SGM) as a cost aggregation function throughout the image pairing, using the Enterprise software from CATALYST. The final products were validated against reference products, and showed excellent agreement with R² values of 0.99. Further, the validation of the DTM and DSM revealed median absolute vertical height error (LE90) across all sites of 1.02 m and 2.58 m, respectively. The orthomosaics were validated with in situ ground control points (GCPs) exhibiting a horizontal Circular Probable Error (CPE) of 1.37 m. The data resulting from this work will be distributed freely with the aim of fostering more scientific studies in the African science community and beyond.Conservation implications: Accurate information about terrain and surface height are crucial inputs to a variety of scientific analysis, which are essential in protected areas, such as flood prediction or fire hazard estimation. Elevation data sets and orthomosaics in very high resolution can therefore serve as a crucial tool to improve park management and foster positive implications on conservation efforts.

Using a fuzzy logic approach to reveal soil-landscape relationships produced by digital soil maps in the humid tropical region of East Java, Indonesia

Digital soil mapping (DSM) has been developed and applied as a cost-effective alternative to conventional mapping. Most DSM studies in predicting soil classes evaluate the accuracy of the digital maps based on the percentage of correctly classified observations over an area or other global statistical measures. There is a lack of local accuracy assessment and spatial comparison of the actual soil-landscape relationships produced by the digital maps. This study aims to address this limitation by examining the use of digital elevation models and their derivatives in predicting the spatial diversity of soil types in the Jember Regency, East Java Province, Indonesia. We evaluated the accuracy of the map using a fuzzy set-map comparison, and in addition, we assessed the soil-landscape relationship of the digital maps. The study used 783 training data in the form of map polygons combined with a suite of covariates representing topography, organisms, and soil moisture. The prediction was carried out using three machine learning techniques: K-nearest neighbors, random forest, and Decision Tree. The soil maps were evaluated using the fuzzy logic metric to determine the global and local agreement between the DSM product and a conventional soil map. The results showed that the global fuzzy matching comparison between the predicted map and the reference map ranged from poor to good (0.30–0.39). However, examining the results locally, very good local fuzzy inference values of 0.69–0.84, were found in the lowland landscapes in the south and highlands in the north. Three digital maps generated by the random forest model combining three covariates showed that the dominant soil in the lowlands near the estuary and the coast was predicted as Typic Endoaquepts, then shifted to Typic Epiaquepts upstream, both of which were Inceptisols. At the top and bottom of the mountain, the predicted soils were Typic Hapludands and Andic Dystudepts, indicating Andisols at the top and a transition from Andisols to Inceptisols at the bottom. This pattern shows that DSM could detect the relationship between soils type formed in local environmental conditions. Evaluating the soil-landscape relationships of digital soil maps can reconcile pedology and digital soil mapping.

Neotectonics and geodynamics of the Streltsovsky ore region according to the analysis of digital elevation models

In the case of underground mining of mineral deposits under difficult mining and geological conditions and at great depths, one of the most urgent problems is the prevention of dangerous geodynamic events. The use of digital elevation models significantly expands the possibilities of preliminary assessment of the potential hazard of their manifestation. This article discusses the results of an assessment of the neotectonics and geodynamics of the Streltsovsky ore region carried out using digital elevation models. The interpretation of the obtained data is based on the concept of lateral tectonic flows adapted for the Far Eastern region of Russia. Digital elevation models based on the GTOPO30 made it possible to identify and evaluate the drift direction of three tectonic flows in the region. The direction determined by the relief coincides satisfactorily with the GPS direction.

Use of Digital Elevation Models to Map Out The Groundwater Resources Base Of Kuje Area to Federal Capital Territory, Abuja, Nigeria


 
 
 This research work examined the use of digital elevation model in the evaluation of groundwater resources in Kuje Area, Nigeria. This was achieved through the acquisition of topographic maps, Digitization of the topographic maps which were glued and interpolated to generate Digital Elevation Models (DEM) and Mapping of groundwater potential areas using ArcGIS 9.2 and ArcView 3.2a software. Findings from this research show that the study area have elevations ranging from 333 m to 429 m above sea level with a moderate groundwater potential in areas with elevation ranging from 286 m and 333 m above sea level. Some areas also have ground water problem, these areas were classified as mountainous areas and are located at very high elevations. The rocky nature of the high elevated environment makes these areas have very little hope of assessing groundwater. It was suggested that government should properly monitor groundwater, inhabitants should be made to accept laws which will help them in the conservation of ground water resources and efforts should also be made by the government towards creating incentives that will encourage people to obey these laws, Conservation methods such as retardation of surface runoff, control of vegetation and groundwater withdrawal rates should be employed.
 
 

Towards Better Visualisation of Alpine Quaternary Landform Features on High-Resolution Digital Elevation Models

Alpine topography is formed by a complex series of geomorphological processes that result in a vast number of different landforms. The youngest and most diverse landforms are various Quaternary sedimentary bodies, each characterised by its unique landform features. The formation of Quaternary sedimentary bodies and their features derive from the dominant building sedimentary processes. In recent years, studies of Quaternary sedimentary bodies and processes have been greatly aided by the use of digital elevation models (DEMs) derived by airborne laser scanning (ALS). High-resolution DEMs allow detailed mapping of sedimentary bodies, detection of surface changes, and recognition of the building sedimentary processes. DEMs are often displayed as hillshaded reliefs, the most common visualisation technique, which suffers from the limitation of a single illumination source. As a result, features can be barely visible or even invisible to the viewer if they are parallel to the light source or hidden in the shadow. These limitations become challenging when representing landforms and subtle landscape features in a diverse alpine topography. In this study, we focus on eleven visualisations of Quaternary sedimentary bodies and their sedimentary and morphological features on a 0.5 m resolution DEM. We qualitatively compare analytical hillshading with a set of visualisation techniques contained in the Raster Visualisation Toolbox software, primarily hillshading from multiple directions RGB, 8-bit sky view factor and 8-bit slope. The aim is to determine which visualisation technique is best suited for visual recognition of sedimentary bodies and sedimentation processes in complex alpine landscapes. Detailed visual examination of previously documented Pleistocene moraine and lacustrine deposits, Holocene alluvial fans, scree deposits, debris flow and fluvial deposits on the created visualisations revealed several small-scale morphological and sedimentary features that were previously difficult or impossible to detect on analytical hillshading and aerial photographs. Hillshading from multiple directions resulted in a visualisation that could be universally applied across the mountainous and hilly terrains. In contrast, 8-bit sky view factor and 8-bit slope visualisations created better visibility and facilitated interpretation of subtle and small-scale (less than ten metres) sedimentary and morphological features.

Digital Elevation Models of Rockfalls and Landslides: A Review and Meta-Analysis

The scope of this paper is to summarize previous research pertaining to the use of digital elevation models (DEMs) and digital terrain models (DTMs) in the study of rockfalls and landslides. Research from 1983 to 2020 was surveyed in order to understand how the spatial resolution of DEMs and DTMs affects landslide detection, validation, and mapping. Another major question examined was the relationship between the DEM resolution and the extent of the rockfall or landslide event. It emerged from the study that, for landslides, the majority of researchers used DEMs with a spatial resolution of between 10 m and 30 m, while for rockfalls, they used DEMs with a spatial resolution of between 5 m and 20 m. We concluded that DEMs with a very high resolution (less than 5 m) are suitable for local-scale occurrences, while medium-resolution (from 20 m to 30 m) DEMs are suitable for regional-scale events. High resolution is associated with high accuracy and detailed structural characteristics, while medium accuracy better illustrates the topographic features. A low pixel size (more than 90 m) is not recommended for this type of research. Susceptibility maps, inventory maps, hazard risk zones, and vulnerability assessments are some of the main tools used in landslide/rockfall investigations, and topographic indexes, methods, models, and software optimize the reliability of the results. All of these parameters are closely related to DEMs and DTMs as the cell size affects the credibility of the final outcome.

Application of Geological Mapping Using Airborne-Based LiDAR DEM to Tunnel Engineering: Example of Dongao Tunnel in Northeastern Taiwan

The use of digital elevation models (DEMs) that use airborne-based light detection and the ranging technique (airborne-based LiDAR) to understand large-scale geological structures has become important in geological surveying and mapping. Taking the Dongao Tunnel area in northeastern Taiwan as the study area, this study used the airborne-based LiDAR DEM and related value-added maps to interpret the topographic and geomorphic features of the area and identify locations for geological investigation. The characteristics of the rock mass were observed on-site and revealed by excavation of the highway tunnel in the study area; they were compared with the interpreted topographic and geomorphic features to determine the potential of using 1 m-resolution LiDAR DEM in geological surveys and in the evaluation of engineering characteristics of underground rock masses. The results of this study demonstrated that the DEM accurately captured geomorphic features: the strata composed of slate and schist had distinct appearances in both the clinometric map and the hillshade map; the locations of faults, lineaments, and drainage were consistent with those observed on-site, and the positions of these features were captured more accurately than those on conventional maps. Evident microrelief features, including the distribution of scarps, erosion gullies, and mini-drainage systems provide an effective basis for interpreting a deep-seated gravitational deformation slope and for an on-site inspection for validation. The use of high-resolution LiDAR DEM to interpret geomorphic features along with geological surveys provides a more comprehensive understanding of the survey area, supporting surveys and geological mapping, revealing the locations of potential slope failures, and enabling the assessment of tunnel engineering risks.

Multiscale Very High Resolution Topographic Models in Alpine Ecology: Pros and Cons of Airborne LiDAR and Drone-Based Stereo-Photogrammetry Technologies

The vulnerability of alpine environments to climate change presses an urgent need to accurately model and understand these ecosystems. Popularity in the use of digital elevation models (DEMs) to derive proxy environmental variables has increased over the past decade, particularly as DEMs are relatively cheaply acquired at very high resolutions (VHR; <1 m spatial resolution). Here, we implement a multiscale framework and compare DEM-derived variables produced by Light Detection and Ranging (LiDAR) and stereo-photogrammetry (PHOTO) methods, with the aim of assessing their relevance and utility in species distribution modelling (SDM). Using a case study on the arctic-alpine plant, Arabis alpina, in two valleys in the western Swiss Alps, we show that both LiDAR and PHOTO technologies can be relevant for producing DEM-derived variables for use in SDMs. We demonstrate that PHOTO DEMs, up to a spatial resolution of at least 1 m, rivalled the accuracy of LiDAR DEMs, largely owing to the customizability of PHOTO DEMs to the study sites compared to commercially available LiDAR DEMs. We obtained DEMs at spatial resolutions of 6.25 cm–8 m for PHOTO and 50 cm–32 m for LiDAR, where we determined that the optimal spatial resolutions of DEM-derived variables in SDM were between 1 and 32 m, depending on the variable and site characteristics. We found that the reduced extent of PHOTO DEMs altered the calculations of all derived variables, which had particular consequences on their relevance at the site with heterogenous terrain. However, for the homogenous site, SDMs based on PHOTO-derived variables generally had higher predictive powers than those derived from LiDAR at matching resolutions. From our results, we recommend carefully considering the required DEM extent to produce relevant derived variables. We also advocate implementing a multiscale framework to appropriately assess the ecological relevance of derived variables, where we caution against the use of VHR-DEMs finer than 50 cm in such studies.