Basis Of Digital Elevation Model Research Articles

Nationwide frequency-dependent seismic site amplification models for Iceland

Seismic wave amplification due to localized site conditions or site-effects, is an important aspect of regional seismic hazard assessment. In the absence of systematic studies of frequency-dependent site-effects during strong Icelandic earthquakes, various local site proxies of large-scale studies in other seismic regions have been used and/or proposed for application in Iceland. Recently, however, earthquake site-effects were rigorously quantified for 34 strong-motion stations in Southwest Iceland for the first time and correlated to distinct Icelandic geological units of hard rock, rock, lava rock, and sedimentary soil. These units are prevalent throughout Iceland and in this study therefore, we present 1) nationwide maps of proxies (e.g. slope, Vs30, geological units) that may contribute to a better estimation of site effects and associated, 2) frequency-dependent site-amplification maps of Iceland relative to the median ground-motion prediction of Rahpeyma et al. (2023) [55]. We particularly focus on the two transform zones of the country, on the basis of digital elevation models and detailed geological maps. Specifically, the frequency-dependent site factors for each geological unit are presented at 1, 2, 5, 7, 10–30 Hz, and PGA. Finally, for comparison, we generate site amplification maps based on recent large-scale models developed in other seismic regions and/or applied in other studies (e.g., ESRM20) as well as various site proxies they are based on (e.g., geology- and slope-based inferred VS30, geomorphological sedimentary thickness). We compare site-proxy maps and amplification maps from both Icelandic and large-scale, non-Icelandic, models. Specifically, neither spatial patterns nor amplification levels in either proxy or amplification maps from large-scale non-Icelandic studies resemble those observed from local quantitative strong-motion research as presented in this study. We attribute the discrepancy primarily to the young geology of Iceland and its formation history. Additionally, this study compares model performance across frequencies by assessing the bias of model predictions against empirical site amplifications in the South Iceland Seismic Zone, accounting for site-to-site variability of residuals indicating the superior performance of the local amplification model. The results presented in this study now allow a more informed estimation of earthquake ground motion amplitudes on various geological units that are expected to result in more reliable and information-based seismic hazard estimates in Iceland.

Morphometric analysis of debris flows basins in the Eastern Rhodopes (Bulgaria) using geospatial technologies

Debris flows are considered as a rapid movement of highly water-saturated colluvial and proluvial deposits. Besides the intensive rainfall and snowmelt, there are several other factors—prerequisites to debris flows: morphometric characteristics, rocks composition, active tectonics and deforestation. The current research is directed to the analysis of morphometric parameters of debris flow areas located in Eastern Rhodopes (Bulgaria). Two types of debris flows are analysed—gully-induced debris flows and stream torrent section with debris flood occurrence. The aim is to determine morphometric indicators to be used for discrimination of debris flow types and further susceptibility assessment. The following parameters are calculated: basin area and length, basin relief, relief ratio, Melton index, slope, topographic wetness index, stream power index and curvature. The analysis shows that slopes in a range 30–45° have most important role, among the other topographic factors, for debris flow initiation. Melton index is a meaningful indicator for discrimination of debris flow types. It is greater than 1 at gully-induced debris flows and much lower at the debris flood section (0.14–0.16). The analysis of curvature rasters, generated as a second derivative of digital elevation model (DEM), shows that the considered gullies are subject of intensive erosion and the process is still active. The research is elaborated in GIS environment on the basis of DEM and field investigations. Terrestrial laser scanning (TLS) of the low part of the basins and debris flow fan is done, and detailed terrain models are developed for the purpose of morphometric analyses.

Flood Inundation Warning and Relief System Based on GIS and Remote Sensing

Abstract: Due to climate change and uncontrolledurbanization, frequencies of floods are increasing these years.In a developing country like India, flood creates a great havocwhich takes many years to get restored. To mitigate the affectof flood disaster, an accurate flood inundation warning isrequired.In this system, a geographic information system (GIS) modelis developed on the basis of Digital Elevation Model (DEM) andthe shapefile of buildings. They accurately analyze the landbehavior in presence of flood and identify the flood inundationrisk of different places. This would be helpful to take activemeasures to mitigate the destruction caused by flood, in timebeing. Global Precipitation Measurement’s (GPM) half-hourlyrain data is used to find the impact of rain on current floodconditions in various areas; this helps to warn the people livingin nearby places, as they also may have threat of life andproperty.This system also contains the flood relief system which is aweb-based system (developed using PHP) having webapplication and MySQL database, to create a platform thatprovides a foundation that prepares the donors to help thevictims of flood with various kinds of donations. This systeminforms the donors by sending an SMS using a GSM module.This is done to prepare the donors with their donations,immediately after the flood warning is released. Thesedonations would equip the authorities to provide essentialneeds of the flood victims. This system is developed forMumbai city, India’s largest city as it is a city affected by floodalmost every year causing great destruction of property andlife. Index Terms: GIS, remote sensing, DEM, Ardunio, MySQL, php, GSM

Spatial distribution and changes of Xing'an permafrost in China over the past three decades

Climate warming causes profound consequences on permafrost distribution throughout the high-latitude regions of the globe. Xing'an permafrost in China is the southernmost part of high-latitude permafrost and is constantly changing. However, understanding on this change process of permafrost is limited. On the basis of digital elevation model (DEM) data, meteorological station, survey data and the meteorological forcing dataset in the northern northeast area in China, we calculated the mean annual ground surface temperature (MAGST), the frost number (Fn) of air temperature (Ta), and the ground surface temperature (GST) with the Fn model. The change in permafrost were analyzed from 1980 to 2010 by statistical and empirical/semi-empirical models. Comparison of the calculated results with the published frozen ground map and survey data, the description on permafrost distribution was more accurate using the Fn of GST than Ta. Permafrost zoning was performed using Fn of GST results and continuous coefficient. The area of permafrost changed from 2.21 × 105 Km2 to 4.87 × 105 Km2. The degradation trend was from low-to high-altitude areas and from continuous to discontinuous permafrost. The permafrost was significantly degraded from the 1980s to the 1990s. The degradation rate slowed down from the 2000s, and some areas have been developed. This work provides basic data and reference for regional permafrost research and project in cold areas.

Low-altitude geophysical magnetic prospecting based on multirotor UAV as a promising replacement for traditional ground survey

The prospects for expanding the mineral resource base in many countries are linked with the exploration of stranded sites localized at unexplored areas with complex natural and landscape conditions that make any ground survey, including magnetic prospecting, difficult and expensive. The current level of geology requires high-precision and large-scale data at the first stages of geological exploration. Since 2012, technologies of aeromagnetic surveying with unmanned aircraft vehicles (UAV) enter the market, but most of them are based on big fixed-wing UAV and do not allow to substantially increase the level of survey granularity compared with traditional aerial methods. To increase the scale of survey, it is necessary to reduce the altitude and speed of flight, for which the authors develop the methodical and technical solutions described in this article. To obtain data at altitudes of 5 m above the terrain even in a rugged relief, we created heavy multirotor UAVs that are stable in flight and may be used in a wide range of environmental conditions (even a moderate snowfall), and develop a special software to generate flight missions on the basis of digital elevation models. A UAV has special design to reduce magnetic interference of the flight platform; the magnetic sensor is hung below the aircraft. This technology was conducted in a considerable amount of magnetic surveys in the mountainous regions of East Siberia between 2014 and 2016. The results of the comparison between airborne and ground surveys are presented, which show that the sensitivity of the developed system in conjunction with low-altitude measurements can cover any geologically significant anomalies of the magnetic field. An unmanned survey is cheaper and more productive; the multirotor-based technologies may largely replace traditional ground magnetic exploration in scales of 1:10,000−1:1000.

A study of clod evolution in simulated rain on the basis of digital elevation models

Soil roughness is a key parameter to our understanding of soil properties and soil-water interaction, most of which occur at millimeter scales. Soil irregularities, such as aggregates, clods and interrill depressions, influence water infiltration and overland flow. The objective of this study is to observe and quantify clod evolution under cumulated precipitation. We prepared two soil trays with loose silt soil and pre-sieved clods put on top, at low and high concentrations. These trays were then subjected to a set of five successive artificial rainfalls. The digital elevation models (DEM) were recorded for each tray, at millimetric resolution, at the initial stage and after each subsequent rainfall. The clods were automatically segmented on the DEM and the diameter, surface area and volume of these clods were measured by computer.The isolated clods showed comparable behavior on both trays. The small clods were almost always decreasing in volume until they disappeared. The other clods swelled during the first rain or the first two rains, and then decreased in area and volume. The decrease was faster for volume than for area. This probably reflected a soil detachment phenomenon, which mostly affected the heights of the clods. On the high concentration tray, the close inter-proximity of the clods induced merging and the formation of blocks.The rate of decrease of clod volume as a function of cumulative precipitation could be modeled using exponential and linear equations. Small and intermediate-sized clods showed an exponential decrease that was smoother as the clod size increased. Large clod volume decrease was almost linear. We were further able to model the trend of the slope parameter of the exponential decrease, as a function of clod size. Our study has shown how the DEM recording and image analysis can be used to quantify the evolution of clods under rainfall, improve our understanding of clod dynamics under rainfall and roughness parameterization. The size dependency of clod volume decrease is important for soil conservation decisions. This will obviously affect crust formation, surface armoring, soil erosion and surface permeability to water and gas.

The methods of geomorphometry and digital soil mapping for assessing spatial variability in the properties of agrogray soils on a slope

The relationships between the morphometric parameters (MPs) of topography calculated on the basis of digital elevation model (АSTER GDEM, 30 m) and the properties of the plow layer of agrogray soils on a slope were analyzed. The contribution of MPs to the spatial variability of the soil moisture reached 42%; to the content of physical clay (<0.01 mm particles), 59%; to the humus content, 46%; to the total nitrogen content, 31%; to the content of nitrate nitrogen, 28%; to the content of mobile phosphorus, 40%; to the content of exchangeable potassium, 45%; to the content of exchangeable calcium, 67%; to the content of exchangeable magnesium, 40%; and to the soil pH, 42%. A comparative analysis of the plow layer within the eluvial and transitional parts of the slope was performed with the use of geomorphometric methods and digital soil mapping. The regression analysis showed statistically significant correlations between the properties of the plow layer and the MPs describing surface runoff, geometric forms of surface, and the soil temperature regime.

A structural-geomorphological interpretation of Southern California shear zones

The neotectonic pop-up structures of Southern California were studied using the structural-geomorphological method, which included the analysis of topographic maps that were constructed on the basis of digital elevation models. The data we obtained are compared with the geological structure and the kinematic model of the block structure of the region based on the analysis of the current movements in accordance with the GPS data. The applicability of this method for neotectonic reconstructions of shear zones is considered. It is shown that the structures that are identified this way may be correlated with the kinematic model of the Southern California block structure that was developed using the GPS data.

A Three‐Dimensional Structure and Process Model for Integrated Hydro‐Geo‐Pedologic Analysis of a Constructed Hydrological Catchment

A structure model describes the boundary geometries and the three‐dimensional solid phase distributions of the catchment. In contrast to an established ecosystem, feedback relations can be assumed for an initial geosystem between the development of spatial structures and the water and element fluxes. The objective was to develop a hydrological catchment model as a three‐dimensional spatial database of the solid phase that allows an integrative analysis, a periodical mass balance, and the generation of distributed model parameters for the developing system. Data were from the constructed catchment “Chicken Creek.” The initial texture and bulk density distributions were generated by imitating sediment dumping, segregation, and compaction. Boundary geometries and changes in surface topography due to erosion and sedimentation processes were quantified on the basis of digital elevation models (DEMs) derived from aerial photographs. The catchment was visualized with the three‐dimensional software GoCad; the “emergence” of the water table and other structures (e.g., soil horizons, root zone) could be spatially assigned and quantified to identify regions with specific processes. A combination of three‐dimensional catchment with time‐dependent two‐dimensional surface models allowed generating the development of spatially distributed erosion–deposition patterns that formed new initial surfaces. The three‐dimensional distributed solid phase structure of the catchment allowed for a more direct comparison with observations using minimal invasive methods. The mass balance of the solids could be related with pedologic development and transfer to other geopedologic systems achieved by adapting sediment transport and deposition in the descriptions of the model. This model may help improve the integrative analysis of hydrological catchments.

Beach-dune degradation in a Mediterranean context of strong development pressures, and the missing integrated management perspective

The Mediterranean coast of Tetouan, south of the Spanish enclave of Ceuta, in Morroco, comprises headland-bound beach-dune systems bordering small coastal plains that are increasingly taken up by socio-economic activities and coastal infrastructure essentially related to tourism development. The 35 km shoreline shows a long-term (multi-decadal) erosional trend due jointly to the damming of the small wadis that hitherto supplied sand to the beach-dune system, the construction of leisure harbours that trap sand and act as boundaries to longshore sand redistribution, and continuous direct dune destruction. Over 95% of the coastal dunes on this microtidal coast have now been destroyed by housing and tourism infrastructure, in a national context marked by a total absence of beach-dune management, and inscribed in an antiquated coastal development setback line of only 3 m relative to the high water level. The short-term sediment budgets of two contrasting beach-dune systems were analysed on the basis of digital elevation models obtained from three successive surveys conducted in February and March 2008 in order to document coastal response patterns to storms under the present conditions of sediment budget stress. Ksar Rimal comprises a narrow beach and a virtually completely destroyed dune, and Cabo Negro exhibits a wider beach and a partially degraded dune. The two beach-dune sites showed balanced sediment budgets, and resilience following a succession of a severe storm (maximum significant wave height (Hs) offshore of 4.2 m), a moderate storm (maximum offshore Hs of 2.8 m) and fair-weather conditions (maximum offshore Hs < 1 m). The survey period is, however, too short to identify the imprint of chronic erosion, and at the short timescale of the study, the resilience shown by both beaches may simply imply that they are presently attuned to the current storm regime. Each beach exhibited a specific resilience mode. Ksar Rimal was dominated by changes essentially limited to the steep narrow beach, involving berm erosion and reformation. The mode on Cabo Negro beach involved sand exchange with the subsisting dune. Continuous dune destruction under development pressures and sand-supply deficit from the nearby wadis will, however, definitely be detrimental to both the protective role of dunes against storms and to beach-dune sand exchanges that contribute to the maintenance of a healthy coastal sediment budget. The case of the Tetouan coast is symptomatic of the situation of large portions of the coast of Morocco now under pressure from development, a situation that, unfortunately, mimicks that of many sectors of depositional coasts in the Mediterranean. Mitigation of coastal erosion requires a firm connection between coastal science and management, but also the rapid implementation of measures aimed at restoring the coastal sediment budget and assuring active beach-dune sand exchange.

Assessment of flood hazard, vulnerability and risk of mid-eastern Dhaka using DEM and 1D hydrodynamic model

Floods are regular feature in rapidly urbanizing Dhaka, the capital city of Bangladesh. It is observed that about 60% of the eastern Dhaka regularly goes under water every year in monsoon due to lack of flood protection. Experience gathered from past devastating floods shows that, besides structural approach, non-structural approach such as flood hazard map and risk map is effective tools for reducing flood damages. In this paper, assessment of flood hazard by developing a flood hazard map for mid-eastern Dhaka (37.16 km2) was carried out by 1D hydrodynamic simulation on the basis of digital elevation model (DEM) data from Shuttle Radar Topography Mission and the hydrologic field-observed data for 32 years (1972–2004). As the topography of the area has been considerably changed due to rapid land-filling by land developers which was observed in recent satellite image (DigitalGlobe image; Date of imagery: 7th March 2007), the acquired DEM data were modified to represent the current topography. The inundation simulation was conducted using hydrodynamic program HEC-RAS for flood of 100-year return period. The simulation has revealed that the maximum depth is 7.55 m at the southeastern part of that area and affected area is more than 50%. A flood hazard map was prepared according to the simulation result using the software ArcGIS. Finally, to assess the flood risk of that area, a risk map was prepared where risk was defined as the product of hazard (i.e., depth of inundation) and vulnerability (i.e., the exposure of people or assets to flood). These two maps should be helpful in raising awareness of inhabitants and in assigning priority for land development and for emergency preparedness including aid and relief operations in high-risk areas in the future.

多時期の空中写真から作成された数値表層モデルを用いた放牧草地における土壌侵食の地形解析

We surveyed soil erosion and slope failure in a grazed pasture in South Hokkaido using digital surface model (DSM) for geomorphic analysis, also, estimated about adaptation to a monitoring in a grazed pasture using DSM. In this study, DSMs were extracted by multi-temporal aerial photographs and digital photogrammetric technique. Digital elevation model (DEM) was extracted by contour map of paper for accuracy validation of DSM absolute accuracy. As a result of DSM accuracy evaluation on the basis of DEM, in all the ages, root mean square deviation of height direction were with satisfactory accuracy. Using extracted multi-temporal DSMs, large-scale soil erosion and slope failure were able to be performed. In addition, growths of grass were able to be grasped. However, it was difficult to extract the minute geomorphic change formed in the grazed pasture. Application of photogrammetric technique to monitoring of grazed pasture definite showed may be able to contribute to preservation of a grazed pasture, and maintenance.