Digital Topographic Model Research Articles

An innovative approach of GSSHA model in flood analysis of large watersheds based on accuracy of DEM, size of grids, and stream density

Distributed modeling approach may have much better performance and accuracy compared with lumped-parameter hydrologic models. The main goals of this research are: investigating the possibility of combining distributed hydrological models with an one-dimensional hydraulic model and simulating waterways in large watersheds with limited hydrological and hydraulic data. Then performing sensitivity analysis on different parameters in order to identify the parameters containing the major influences on results. In the current research, an innovative approach in Gridded Surface Subsurface Hydrologic Analysis (GSSHA) model, the cross-sections of all 414 waterways in the 3450 km2 Karvandar watershed, used for flow routing calculations, are uniquely extracted. Then, the effect of three essential factors are evaluated. These factors are accuracy of the digital topographic model, cell size of grid network, and density of streams, on the results of GSSHA model simulations. This watershed is located in southeastern Iran, has a dry climate with limited available hydrological data. Results showed that peak discharges obtained from the GSSHA model, developed based on a DEM with a spatial resolution of 12.5 m, are slightly (< 4%) lower than the corresponding values ​​in the GSSHA model with a 30 m DEM resolution. This fact confirms that the use of the topographic model with a lower spatial resolution has no substantial effects on the accuracy of simulation. Also, the peak discharges increased significantly (44% to 57%) by increasing the density of waterways in the GSSHA model. Furthermore, results showed that peak discharge obtained from three models with grid cell sizes of 100, 150, and 200 m (base model), are close together. Comparing with two models of coarser grids (250 and 300 m), significant differences observed, which indicated that the grids larger than 200 m could induce substantial errors in results.

Construction of Topographic/Hydrologic Data using DEM and its Service 2

In addition to a total of 20 types of topography/moisture analysis maps that have already been built using a digital topographic model (DEM), in this study, a total of 32 types including 26 types of topographic analysis diagrams and 6 types of hydrological analysis diagrams were performed through various topography/hydraulic analysis. Additional species were built. As with the existing established data, the construction range is the whole of South Korea, the resolution is 30 m, and the coordinate system is UTM-K coordinates. The constructed data format is provided in three formats: ASCII, ARCGIS GRID, and GEOTIFF. All these topographic / hydrological analysis data can be downloaded free of charge from the Environmental Big Data Platform (www.bigdata-environment.kr).

New geoid model for Egypt using the shallow-layer method and its validation

Geoid determination for Egypt faces several challenges. There are large gravity data gaps, gravity data come from different sources, were measured during different decades, and some lack information about their precision. The aim of the paper is to find out a new geoid model for Egypt using the advantages of the shallow-layer method. The shallow-layer method is different from the traditional Stokes and Molodenesky geoid determination methods as it comes from the definition of the geoid itself. In our work, we apply the shallow-layer method to determine a 5′ × 5′ geoid model for Egypt which ranges from (21∘ ≤ ϕ ≤ 32∘; 24∘ ≤ λ ≤ 37∘). The global digital topographic model DTM2006.0, the Danish National Space Center DNSC08 model, the EGM2008 gravity field model, and the CRUST2.0 crust model were used to distinguish boundaries for the shallow-layer and determine its interior structure. To validate and test the computed geoid, four gravimetric geoid models for Egypt were computed using different techniques, the Meissl-geoid using modified Stokes kernel after Meissel, the Wong-geoid using modified Stokes kernel after Wong and Gore, the Heck-geoid using modified Stokes kernel after Heck and Grüninger, and the window-geoid using window technique. All the computed geoid models were validated using the available GPS benchmark stations in Egypt. The difference between the computed geoid models and GPS benchmark station shows that the shallow-layer method gives the most precise geoid with the narrowest range and smallest standard deviation. The standard deviation of geoid differences for the geoid computed using the shallow-layer method (Shen-geoid) drops by about 0.37 m compared to the Stokes/Meissl geoid, which means that the calculated Shen-geoid fits GPS benchmarks better than the computed gravimetric geoid (using the available gravity data) for Egypt. The results demonstrate that the shallow-layer method can estimate the geoid at higher accuracy.

Construction of Topographic/Hydrologic Data using DEM and Its Service

In this study, 10 types of terrain analysis maps and 10 types of hydrology analysis maps were constructed through various topographic/hydrological analysis using a digital topographic model (DEM). The construction range is for the entire South Korea, the resolution is 30m, and the coordinate system is UTM-K coordinates. The constructed data format is provided in three formats: ASCII, ARCGIS GRID, and GEOTIFF. In addition, all data is provided in the form of the above three data format for whole of South Korea and each administrative district. All of these topographic/hydrological analysis data can be downloaded for free from the environment big data platform (www.bigdata-environment.kr).

Topographic and Geomorphological Mapping and Analysis of the Chang'E-4 Landing Site on the Far Side of the Moon

The Chinese lunar probe Chang'E-4 successfully landed in the Von Kármán crater on the far side of the Moon. This paper presents the topographic and geomorphological mapping and their joint analysis for selecting the Chang'E-4 landing site in the Von Kármán crater. A digital topographic model (&lt;small&gt;DTM&lt;/small&gt;) of the Von Kármán crater, with a spatial resolution of 30 m, was generated through the integrated processing of Chang'E-2 images (7 m/pixel) and Lunar Reconnaissance Orbiter (&lt;small&gt;LRO&lt;/small&gt;) Laser Altimeter (&lt;small&gt;LOLA&lt;/small&gt;) data. Slope maps were derived from the &lt;small&gt;DTM&lt;/small&gt;. Terrain occlusions to both the Sun and the relay satellite were studied. Craters with diameters ≥ 70 m were detected to generate a crater density map. Rocks with diameters ≥ 2 m were also extracted to generate a rock abundance map using an &lt;small&gt;LRO&lt;/small&gt; narrow angle camera (&lt;small&gt;NAC&lt;/small&gt;) image mosaic. The joint topographic and geomorphological analysis identified three subregions for landing. One of them, recommended as the highest-priority landing site, was the one in which Chang'E-4 eventually landed. After the successful landing of Chang'E-4, we immediately determined the precise location of the lander by the integrated processing of orbiter, descent and ground images. We also conducted a detailed analysis around the landing location. The results revealed that the Chang'E-4 lander has excellent visibility to the Sun and relay satellite; the lander is on a slope of about 4.5° towards the southwest, and the rock abundance around the landing location is almost 0. The developed methods and results can benefit future soft-landing missions to the Moon and other celestial bodies.

CREATION OF A DIGITAL TOPOGRAPHIC MODEL IN EXTREME AREAS ON THE TERRITORY OF SOUTH-WESTERN BULGARIARILA MOUNTAIN

The subject of the research is to create a digital topographic model (DTM) on the territory of Rila Mountain in order to further local modeling of the geoid. The data obtained from this model, in the form of planar and altitude coordinates, are used to determine the terrain correction and calculate the complete Bougue anomalies. The information from the DTM in terms of altitude can serve as an initial value of the normal altitude in the interpolation calculations and determination of the transformation parameters when filling in the data for modelling the geoid (quasi-geoid).

PRIMo: Parallel raster inundation model

Simulation of flood inundation at metric resolution is important for making hazard information useful to a wide range of end-users involved in flood risk management, and addressing the alarming increase in flood losses that have been observed over recent decades. However, high data volumes and computational demands make this challenging over large spatial extents comparable to the metropolitan areas of major cities where flood impacts are concentrated, especially for time-sensitive applications such as forecasting and repetitive simulation for uncertainty assessment. Additionally, several factors present difficulties for numerical solvers including combinations of steep and flat topography that promote transcritical flows, the need to resolve flow in relatively narrow features such as drainage channels and roadways in urban areas which channel flood water during extreme events, and the need to depict compound hazards resulting from the interaction of pluvial, fluvial and coastal flooding. A new flood inundation model is presented here to address these challenges. The Parallel Raster Inundation Model (PRIMo) solves the shallow-water equations on an upscaled grid that is far coarser than the underlying raster digital topographic model (DTM), and uses a subgrid modeling approach so that the solution benefits from DTM-scale topographic data. Additionally, an approximate Riemann solver is applied in an innovative way to integrate fluxes between cells, as needed to update the solution by the finite volume method, which makes the method applicable to subcritical, supercritical and transcritical flows. PRIMo is implemented using a two-dimensional domain decomposition approach to Single Process Multiple Data (SPMD) parallel computing, and overlapping communications and computations are implemented to yield ideal parallel scaling for well-balanced test cases. With both a subgrid model and ideal parallel scaling, the model can scale to meet the demands of any application. Several benchmarks are presented to demonstrate predictive skill and the potential for timely, whole-city, metric-resolution flooding simulations. Limitations of the methods and opportunities for improvements are also presented.

The Rock–Water–Ice Topographic Gravity Field Model RWI_TOPO_2015 and Its Comparison to a Conventional Rock-Equivalent Version

RWI_TOPO_2015 is a new high-resolution spherical harmonic representation of the Earth’s topographic gravitational potential that is based on a refined Rock–Water–Ice (RWI) approach. This method is characterized by a three-layer decomposition of the Earth’s topography with respect to its rock, water, and ice masses. To allow a rigorous separate modeling of these masses with variable density values, gravity forward modeling is performed in the space domain using tesseroid mass bodies arranged on an ellipsoidal reference surface. While the predecessor model RWI_TOPO_2012 was based on the \(5'\times 5'\) global topographic database DTM2006.0 (Digital Topographic Model 2006.0), the new RWI model uses updated height information of the \(1'\times 1'\) Earth2014 topography suite. Moreover, in the case of RWI_TOPO_2015, the representation in spherical harmonics is extended to degree and order 2190 (formerly 1800). Beside a presentation of the used formalism, the processing for RWI_TOPO_2015 is described in detail, and the characteristics of the resulting spherical harmonic coefficients are analyzed in the space and frequency domain. Furthermore, this paper focuses on a comparison of the RWI approach to the conventionally used rock-equivalent method. For this purpose, a consistent rock-equivalent version REQ_TOPO_2015 is generated, in which the heights of water and ice masses are condensed to the constant rock density. When evaluated on the surface of the GRS80 ellipsoid (Geodetic Reference System 1980), the differences of RWI_TOPO_2015 and REQ_TOPO_2015 reach maximum amplitudes of about 1 m, 50 mGal, and 20 mE in terms of height anomaly, gravity disturbance, and the radial–radial gravity gradient, respectively. Although these differences are attenuated with increasing height above the ellipsoid, significant magnitudes can even be detected in the case of the satellite altitudes of current gravity field missions. In order to assess their performance, RWI_TOPO_2015, REQ_TOPO_2015, and RWI_TOPO_2012 are validated against independent gravity information of current global geopotential models, clearly demonstrating the attained improvements in the case of the new RWI model.

Delineation and assessment of Central Indian Suture through lineament extraction approach using Remote Sensing and Geographic Information System

Lineament extraction approach allowed mapping of larger number of lineaments in a classical manner in tectonic and structural studies. In the present study, various techniques were adopted to extract lineaments using Landsat ETM+ images. To remove the biasness of the images, some pre-processing techniques like stream ordering, band differencing, colour texturing were employed to enhance the edges of the structural features. Extracted lineaments and its distribution and orientation were mapped using ArcGIS Spatial analyst tool. Results of the study showed maximum number of lineaments were oriented in the ENE–SWS direction with 63° overall inclination. Accuracy assessment and validation were made with respect to visual interpretation and overlaying the lineament on Digital Topographic Model as well as with respect to an existing geological lineament map of the study site. The result of accuracy assessment indicates higher compatibility of Central Indian Suture with the geological map of the study area.

Environmental Reconstruction of the Area Of Roman Brigetio (Komárom, Hungary)

The purpose of our research is the environmental reconstruction of an important part of the Ripa Pannonica (limes), the Roman frontier system in Pannonia province. The study area is between the present Komarom, Tata, Dunaalmas settlements in Hungary. The legionary fortress of Brigetio was located along the Danube, forming part of the town of Komarom, Hungary. The camp and the settlement were bordered by the Danube on the north and by an aband oned river subchannel on the south. Using this riverbed and the valley of the Fenyes stream flowing into it the Romans constructed a dam and created a wetland area, which might have had a defensive role. We prepared an environmental reconstruction based on geomorphological research, field work, GIS analysis, archive maps and historical sources and made the reconstructed digital topographic model of the study area. We also assessed the relationship between the geomorphological features and the anthropological landscape-shaping impacts. The settlement lied on the higher level of floodplain of the Danube river. The accumulation of the higher floodplain's sediments can be dated to the end of the Atlantic and first half of the Subboreal. The higher floodplain was finally formed in the last third of the Subboreal phase. At this time, at the end of the Late Bronze Age, the riverbed (the Danube subchannel) lying south of Brigetio's island was formed. This riverbed became abandoned at the end of the Subboreal phase, in the Early Iron Age. The marsh resulting from the Roman dam construction was present up until 1747, when S. Mikoviny dismantled the flood-gates and drained the area. Its history can be followed on archive maps, such as G. G. P r i o r a t o (1672), L. F. M a r s i g l i (1726) and S. M i k o v i n y (1746).

Improved Geoid Determination Based on the Shallow-Layer Method: A Case Study Using EGM08 and CRUST2.0 in the Xinjiang and Tibetan Regions

In this paper we present the concepts and realization of the shallow-layer Shen geoid determination method, which is quite different from the classical geoid modeling methods (Stokes' method, Molodenskii's method, etc.), for determining the global or regional geoids. This method takes full advantage of the precise Earth gravity field model EGM2008, digital topographic model DTM2006.0 and global crust model CRUST2.0 of a shallow layer, a layer from the Earth's surface to a depth. As a case study this method is applied to the determination of a 5' × 5' geoid over the Xinjiang and Tibetan regions, which ranges from latitude 25 to 50°N and longitude 70 to 100°E. The modeled 5' × 5' regional geoid is compared with the EGM2008 geoid model in the same study area and validated by 21 GPS/leveling benchmarks (GPSBMs) distributed sparsely in the Xinjiang area. The results show that the regional geoid reaches an accuracy of ~18 cm and agrees with the GPSBMs better than the EGM2008 geoid in the Xinjiang region.

Hydrologic Versus Biogeochemical Controls of Denitrification in Tidal Freshwater Wetlands

Tidal freshwater wetlands (TFW) alter nitrogen concentrations in river water, but the role of these processes on a river’s downstream nitrogen delivery is poorly understood. We examined spatial and temporal patterns in denitrification in TFW of four rivers in North Carolina, USA and evaluated the relative importance of denitrification rate and inundation on ecosystem-scale N2 efflux. An empirical model of TFW denitrification was developed to predict N2 efflux using a digital topographic model of the TFW, a time series of water level measurements, and a range of denitrification rates. Additionally, a magnitude-frequency analysis was performed to investigate the relative importance of storm events on decadal patterns in N2 efflux. Spatially, inundation patterns exerted more influence on N2 efflux than did the range of denitrification rate used. Temporal variability in N2 efflux was greatest in the lower half of the tidal rivers (near the saline estuary) where inundation dynamics exerted more influence on N2 efflux than denitrification rate. N2 efflux was highest in the upper half of the rivers following storm runoff, and under these conditions variation in denitrification rate had a larger effect on N2 efflux than variability in inundation. The frequency-magnitude analysis predicted that most N2 efflux occurred during low flow periods when tidal dynamics, not storm events, affected TFW inundation. Tidal hydrology and riparian topography are as important as denitrification rate in calculating nitrogen loss in TFW; we present a simple empirical model that links nitrogen transport in rivers with loss due to denitrification in TFW.

A novel approach for constructing a 3D model based on registering a mono image on a 3D model, applicable in Digital Earth

The effect of Digital Earth on our life is vital. Developing and updating Geospatial data in Digital Earth is also essential. This paper presents the application of a new approach of image registration in Digital Earth. The approach was developed based on registering a mono photograph on a master 3D model. The result is a 3D vector model, which can be broadly applied in visualisation, mapping, geographic information system (GIS), planning, change detection, as well as Digital Earth. The approach does not require parameters of correction for transformation. The accuracy of the output depends on the accuracy of the master data. This approach is very versatile and able to register any image on the digital elevation model, digital surface model and topographic 3D model.

Parameterization of topographic effect on surface solar radiation

Topographic impact on the surface solar (shortwave (SW)) radiation was investigated using a 40 m high‐resolution digital topographic data model and a radiative transfer model. With applications to the complex terrain of Taiwan, we found that the spatial variation of the surface SW radiation has a strong diurnal cycle. The standard deviation of the SW radiation, σf, over Taiwan is nearly constant for a given solar zenith angle (SZA). The maximum σf occurs at SZA ∼55°, corresponding to midmorning (early morning) and midafternoon (late afternoon) in winter (summer). For a spatial resolution of 40 m, the σf over Taiwan attains a maximum value of 300 W m−2, which is ∼50% of the domain mean SW radiation. The topographic impact on the spatial variation of SW radiation increases with decreasing grid box size, Δx. In mesoscale land and atmospheric models, Δx is small, and the topographic impact is strong. Over Taiwan, the standard deviation of the difference between the daily mean SW radiation computed with a spatial resolution of 40 m and that computed with degraded spatial resolution reaches 25 W m−2 for Δx = 1 km and 8 W m−2 for Δx = 10 km, indicating the importance of topographic impact on the surface SW radiation in mesoscale land and atmospheric models. We developed a parameterization of the topographic impact on the surface SW radiation that scales the SW radiation computed for a flat surface without shading by surrounding terrains. The scaling is separately applied to the direct and diffuse radiation. It is applicable to all clear, aerosol‐laden, and cloudy conditions and to all spatial resolutions with Δx &gt; 40 m.

Análise da variação dos elementos do campo de gravidade na região do Aqüifero Guarani a partir dos dados GRACE

This work estimates the variation of the gravity field elements in a period of two years and three months - April 2002 to July 2004 - using the GRACE mission data in the Guarani aquifer region; these changes are the sum of all the gravity changes that are caused by variations from mass distribution of the Earth's surface and by the deformation of the solid Earth in response to these mass variations. The solutions have been calculated only from the disturbances of the satellite orbits and do not depend on the gravity data available in the oceanic and continental areas. The calculations of the Earth's gravity field monthly solutions by using the GRACE mission data, considering the spherical harmonics, i.e., the Stokes coefficients, for the global gravity field, up to degree and order 150 (February/2003 to July/2004) and 120 (April, August and November 2002), have been transformed in geoidal height and free-air anomaly grids, with the respective associated errors. A linear 3-D inversion using the residual geoid height supplied the three dimensional density distribution, showing that the use of the GRACE data in investigation of the water mass variability in Guarani aquifer is feasible. A Bouguer anomaly profile, calculated by using the GRACE free-air anomaly and a digital topographic model data, was used in order to estimate the water mass variation in the Guarani aquifer region.

Analysis of Landsat 5 TM Images for Monitoring the State of Restoration of Abandoned Quarries

Quarrying causes high damage to the ecosystems, consequently abandoned sites monitoring is a very important issue. This study describes a methodology to assess the sites’ state of restoration through the analysis of Landsat 5 TM images. The procedure does not require any radiometric corrections for atmospheric effects nor for irradiance effects related to the relief. Such corrections would require a model for the atmosphere at the time the images were taken and a detailed digital topographic model (DEM). In addition, the use of a GIS allowed a direct model calibration from satellite images without any previous field inventory and measurements. The results from the proposed procedure have been compared to in-situ surveyed data.

Numerical simulation of pyroclastic density currents on Campi Flegrei topography: a tool for statistical hazard estimation.

We describe a numerical simulation of both concentrated and dilute gravity-driven pyroclastic flows on a digital topographic model of the Campi Flegrei volcanic field. Families of numerical flows are generated by sampling a multi-dimensional matrix of vent coordinates, flow properties and dynamical parameters within a wide range of values. Hazard maps are constructed from the data base of simulated flows, using a mixed deterministic–statistical approach. The set of probable vents covers the area of recent eruptions. Results show the key role of topography in controlling the flow dispersion. The maximum hazard appears to be the NE sector of the caldera. Flows in the eastern sector, including the city of Naples, are shown to be efficiently hindered by the Posillipo and Camaldoli hills at the caldera borders, thus reducing the hazard. The results represent the first physically based estimate of hazard from pyroclastic flows in this densely populated area, and can be used for civil defence purposes.

Spatial prediction of coral reef habitats: integrating ecology with spatial modeling and remote sensing

Spatial prediction of coral reef habitats and coral reef community components was approached on the basis of the 'predict first, classify later' paradigm. Individual community compo- nents (biotic and geomorphologic bottom features) were first predicted and then classified into com- posite habitats. This approach differs from widely applied methods of direct classification based on remote sensing only. In situ coral reef community-condition assessment was first used to measure a response variable (percentage cover of habitat). Reef bottom features (topographic complexity, sand- sediment, rock-calcareous pavement and rubble) were then predicted using generalized additive models (GAMs) applied to continuous environmental maps, high-resolution Ikonos satellite images and a reef digital topographic model (DTM). Next, using GAMs on newly created bottom maps, mod- els were fitted to predict coral community components (hard coral, sea-grass, algae, octocorals). At this stage, high-resolution maps of the geomorphologic and biotic components of the coral reef com- munity at an experimental site (Akumal Reef in the Mexican Caribbean) were produced. Coral reef habitat maps were derived using GIS following a hierarchical classification procedure, and the result- ing merged map depicting 8 habitats was compared against thematic maps created by traditional supervised classification. This general approach sets a baseline for future studies involving more complex spatial and ecological predictions on coral reefs.

Estimation of the energy balance of the Dischma valley

A method is presented which allows the computation of the terms of the energy balance for the whole area of an Alpine valley. The method is based on measurements at three stations, a digital topographic model, a vegetation map and surface temperature measurements. The results are given in shadow maps. The distribution of the radiation balance is mainly determined by the topographic exposure, while the latent heat flux is determined mainly by vegetation.