Analysis Of Digital Elevation Models Research Articles

Amalgamation in landslide maps: effects and automatic detection

Abstract. Inventories of individually delineated landslides are a key to understanding landslide physics and mitigating their impact. They permit assessment of area–frequency distributions and landslide volumes, and testing of statistical correlations between landslides and physical parameters such as topographic gradient or seismic strong motion. Amalgamation, i.e. the mapping of several adjacent landslides as a single polygon, can lead to potentially severe distortion of the statistics of these inventories. This problem can be especially severe in data sets produced by automated mapping. We present five inventories of earthquake-induced landslides mapped with different materials and techniques and affected by varying degrees of amalgamation. Errors on the total landslide volume and power-law exponent of the area–frequency distribution, resulting from amalgamation, may be up to 200 and 50%, respectively. We present an algorithm based on image and digital elevation model (DEM) analysis, for automatic identification of amalgamated polygons. On a set of about 2000 polygons larger than 1000 m2, tracing landslides triggered by the 1994 Northridge earthquake, the algorithm performs well, with only 2.7–3.6% incorrectly amalgamated landslides missed and 3.9–4.8% correct polygons incorrectly identified as amalgams. This algorithm can be used broadly to check landslide inventories and allow faster correction by automating the identification of amalgamation.

Analysis of digital elevation models of the geological surveys of the Elkon uranium-ore district (Aldan-Stanovoi Shield)

This work discusses the satellite-derived synthetic aperture radar (SAR) data to distinguish and justify the inner structures of ore districts located within the shields of ancients platforms activated in the Mesozoic. For this purpose, the SAR-based digital elevation models developed for the Elkon uranium-ore district in the Aldan-Stanovoi Shield were specially processed and lineaments and a set of other statistical parameters were calculated using WinLessa software. The processed data of the digital elevation models allowed us to identify new structural features of the Elkon ore district and evaluate its uranium-ore potential.

Monitoring of local coastal geosystems of the Bratsk reservoir

According to the comparative analysis of digital elevation models (DEM) based on large scale topographic surveying at the Bykovo site, a 746 m² maximal extension of landslide movement area was revealed in 2006, which was caused by maximum rainfall and the reservoir water level highest in the observation period. The areas prone to erosional form development on the landslide slope increased on 100 m². It was established that the Rassvet site on 2000 m extent in alluvial and deluvial loams and sandy loams with interlayers of medium sands is exposed to abrasive wash-out. The width of the shore slope edge retreat ranged from 0 to 8 m during the last three years. According to GPS survey data, the maximum volume of washed-out soil material reached 13860.0 м 3 over the 2006–2007 period. The total volume of the gullies in the edge of abrasive bench amounted to 1360.1 м 3 (2007). The volume of soil, lost at the Zakoryukovo site in the loess-like sediments as a result of a small shore edge retreat and erosional processes constituted 2590 м 3 in the same period. The highest volume increase (on 4486.34 m³ from 2004 to 2008) was revealed at karst-erosional mechanism on the Khadahan site. Based on interpretation of images (1971—1980), the mid-term dynamics of linear growth of shore gullies on the abrasive Uley site ranged from 0 to 44 m, average growth rate accounted for 1-2 m, with maximum of 4 m per year. At the present stage the shore zone of the Bratsk reservoir is marked by lack of stabilization of abrasion processes. The response reaction of local geosystems (dynamics of the processes, their interaction, and environment change) is characterized by a certain cyclicity corresponding to water level fluctuations.

A novel method for improved DEM deformation detection

The deformation detection method without control points is one of the key techniques for multi-temporal digital elevation model (DEM) analyses, and represents an attractive and difficult research topic. A novel method for improved DEM deformation detection is proposed in this paper, based on the Least Z-Difference algorithm with differential model (DM- LZD). In the new method, an additional parameter is employed to improve the weighting function for the observations in the matching algorithm. Three indexes are designed to give an in-depth and quantitative analysis of the performance, according to the possible two types of errors occurring in the weighting function. The experimental result, based on the simulated dataset, shows that with an appropriate additional parameter it will achieve a better balance between the deformation-detecting ability and the matchingaccuracy, and so generates better performance.

Aplicación de SIG para la caracterización hidrogeológica de sistemas dunares (Erg Chebbi, Marruecos)

Hydrogeological studies in remote areas are difficult to tackle and often logistically complicated. However, in some of these areas the exploitation of groundwater resources is essential for the survival of the communities that inhabit them. The dunes of Erg Chebbi configure a free aquifer about 100 km 2 in area. With an average annual rainfall of less than 150 mm, Erg Chebbi represents an extremely delicate hydrological system that requires a very well designed exploitation to enable a sustainable development. This paper addresses the hydrogeological characterization of an erg system by means of Geographic Information Systems (GIS) (ArcGis 9.3 y Global Mapper v.12), Digital Elevation Model (DEM) and geological information analysis. Results allowed the characterization the dune system and the setting of a hydrogeological model, consistent with field data. The results are relevant to the management of the groundwater exploitation in the studied system, and highlight the utility of this methodology to the characterization of other areas with similar characteristics.

A multi‐dimensional analysis of pro‐glacial landscape change at Sólheimajökull, southern Iceland

AbstractPro‐glacial landscapes are some of the most active on Earth. Previous studies of pro‐glacial landscape change have often been restricted to considering either sedimentological, geomorphological or topographic parameters in isolation and are often mono‐dimensional. This study utilized field surveys and digital elevation model (DEM) analyses to quantify planform, elevation and volumetric pro‐glacial landscape change at Sólheimajökull in southern Iceland for multiple time periods spanning from 1960 to 2010. As expected, the most intense geomorphological changes persistently occurred in the ice‐proximal area. During 1960 to 1996 the pro‐glacial river was relatively stable. However, after 2001 braiding intensity was higher, channel slope shallower and there was a shift from overall incision to aggradation. Attributing these pro‐glacial river channel changes to the 1999 jökulhlaup is ambiguous because it coincided with a switch from a period of glacier advance to that of glacier retreat. Furthermore, glacier retreat (of ~40 m yr−1) coincided with ice‐marginal lake development and these two factors have both altered the pro‐glacial river channel head elevation. From 2001 to 2010 progressive increase in channel braiding and progressive downstream incision occurred; these together probably reflecting stream power due to increased glacier ablation and reduced sediment supply due to trapping of sediment by the developing ice‐marginal lake. Overall, this study highlights rapid spatiotemporal pro‐glacial landscape reactions to changes in glacial meltwater runoff regimes, glacier terminus position, sediment supply and episodic events such as jökuhlaups. Recognizing the interplay of these controlling factors on pro‐glacial landscapes will be important for understanding the geological record and for landscape stability assessments. Copyright © 2014 John Wiley & Sons, Ltd.

Incorporating DEM uncertainty in coastal inundation mapping.

Coastal managers require reliable spatial data on the extent and timing of potential coastal inundation, particularly in a changing climate. Most sea level rise (SLR) vulnerability assessments are undertaken using the easily implemented bathtub approach, where areas adjacent to the sea and below a given elevation are mapped using a deterministic line dividing potentially inundated from dry areas. This method only requires elevation data usually in the form of a digital elevation model (DEM). However, inherent errors in the DEM and spatial analysis of the bathtub model propagate into the inundation mapping. The aim of this study was to assess the impacts of spatially variable and spatially correlated elevation errors in high-spatial resolution DEMs for mapping coastal inundation. Elevation errors were best modelled using regression-kriging. This geostatistical model takes the spatial correlation in elevation errors into account, which has a significant impact on analyses that include spatial interactions, such as inundation modelling. The spatial variability of elevation errors was partially explained by land cover and terrain variables. Elevation errors were simulated using sequential Gaussian simulation, a Monte Carlo probabilistic approach. 1,000 error simulations were added to the original DEM and reclassified using a hydrologically correct bathtub method. The probability of inundation to a scenario combining a 1 in 100 year storm event over a 1 m SLR was calculated by counting the proportion of times from the 1,000 simulations that a location was inundated. This probabilistic approach can be used in a risk-aversive decision making process by planning for scenarios with different probabilities of occurrence. For example, results showed that when considering a 1% probability exceedance, the inundated area was approximately 11% larger than mapped using the deterministic bathtub approach. The probabilistic approach provides visually intuitive maps that convey uncertainties inherent to spatial data and analysis.

АДАПТИВНАЯ СТРАТЕГИЯ ОТБОРА ПРОБ ДЛЯ ОЦЕНКИ ПРОСТРАНСТВЕННОЙ ОРГАНИЗАЦИИ СООБЩЕСТВ ПОЧВЕННЫХ ЖИВОТНЫХ УРБАНИЗИРОВАННЫХ ТЕРРИТОРИЙ НА РАЗЛИЧНЫХ ИЕРАРХИЧЕСКИХ УРОВНЯХ

<p>In work the algorithm of adaptive strategy of optimum spatial sampling for studying of the spatial organisation of communities of soil animals in the conditions of an urbanization have been presented. As operating variables the principal components obtained as a result of the analysis of the field data on soil penetration resistance, soils electrical conductivity and density of a forest stand, collected on a quasiregular grid have been used. The locations of experimental polygons have been stated by means of program ESAP. The sampling has been made on a regular grid within experimental polygons. The biogeocoenological estimation of experimental polygons have been made on a basis of A.L.Belgard's ecomorphic analysis. The spatial configuration of biogeocoenosis types has been established on the basis of the data of earth remote sensing and the analysis of digital elevation model. The algorithm was suggested which allows to reveal the spatial organisation of soil animal communities at investigated point, biogeocoenosis, and landscape.</p> <p><em>Keywords: adaptive strategy, sampling, ecomorphic analysis, biogeocoenosis, soil animals</em></p>

Tracking sediment provenance and erosional evolution of the western Greater Caucasus

ABSTRACTThis article investigates landscape characteristics and sediment composition in the western Greater Caucasus by using multiple methods at different timescales. Our ultimate goal is to compare short‐term versus long‐term trends in erosional processes and to reconstruct spatio‐temporal changes in sediment fluxes as controlled by partitioning of crustal shortening and rock uplift in the orogenic belt. Areas of active recent uplift are assessed by quantitative geomorphological techniques [digital elevation model (DEM) analysis of stream profiles and their deviation from equilibrium] and compared with regions of rapid exhumation over longer time intervals as previously determined by fission‐track and cosmogenic‐nuclide analyses. Complementary information from petrographic and heavy‐mineral analyses of modern sands and ancient sandstones is used to evaluate erosion integrated throughout the history of the orogen. River catchments displaying the highest relief, as shown by channel‐steepness indices, correspond with the areas of most rapid exhumation as outlined by thermochronological data. The region of high stream gradients is spatially associated with the highest topography around Mount Elbrus, where sedimentary cover strata have long been completely eroded and river sediments display the highest metamorphic indices and generally high heavy‐mineral concentrations. This study reinforces the suggestion that the bedrock–channel network can reveal much of the evolution of tectonically active landscapes, and implies that the controls on channel gradient ultimately dictate the topography and the relief along the Greater Caucasus. Our integrated datasets, obtained during a decade of continuing research, display a general agreement and regularity of erosion patterns through time, and consistently indicate westward decreasing rates of erosional unroofing from the central part of the range to the Black Sea. Copyright © 2014 John Wiley & Sons, Ltd.

Insights into deglaciation of the largest ice-free area in the South Shetland Islands (Antarctica) from quantitative analysis of the drainage system

A quantitative geomorphic analysis of the drainage system on Byers Peninsula, Livingston Island, has been carried out in order to study the relief evolution, glacial history and possible neotectonic influence on the largest ice-free area of the South Shetlands archipelago. Aerial photographs, SAR data from RADARSAT-2 satellite, field work, a digital elevation model and GIS spatial analysis have been used to identify, map and study the existing drainage basins. A series of morphometric parameters have been studied in 30 selected basins in order to characterize their shape as well as the drainage network. Results in morphometric parameters reveal elongation trends in the shape of basins and a limited hierarchical network, common of a youthful stage of landscape evolution models.Several morphometric indexes (hypsometric integral, hypsometric curves, SL index, transverse topographical drainage basin asymmetry-T-Factor) have been used to study possible controls on drainage development. Results have been discussed in relation to relief and drainage evolution linked to the spatial distribution of lithological units and structural framework. T-Factor shows an apparently disorganized pattern and absence of tectonic influence. However, there are local values of second order basin asymmetry directions and magnitudes, which could reflect a succession of master rills through time, related to the changes in water supply during the deglaciation history of Byers Peninsula. Hypsometric values and curves of basins are also mainly related to a young stage of landscape evolution. Analysis of hypsometric integrals together with T-Factor index has allowed us to establish a possible deglaciation model on Byers Peninsula, which successfully explains the results. Areas of different landscape evolution stage are linked in space and support the hypothesis of local glacial centers during the ice cover retreat process. SL index results do not show the same pattern in results, which could be due to differences between incision and lateral shifting ratios.Quantitative geomorphic analysis indicates that during the deglaciation of Byers Peninsula, at least three areas acted as local glacial centers (NW, central and Rotch Dome area). Changes in index results clearly show a different behavior between two areas; distal areas and proximal areas close to the glacial centers. Morphometric indexes have demonstrated their being useful tools to provide information on the glacial history in recently deglaciated Antarctic areas.

Vesta’s north pole quadrangle Av-1 (Albana): Geologic map and the nature of the south polar basin antipodes

As part of systematic global mapping of Vesta using data returned by the Dawn spacecraft, we have produced a geologic map of the north pole quadrangle, Av-1 Albana. Extensive seasonal shadows were present in the north polar region at the time of the Dawn observations, limiting the ability to map morphological features and employ color or spectral data for determination of composition. The major recognizable units present include ancient cratered highlands and younger crater-related units (undivided ejecta, and mass-wasting material on crater floors). The antipode of Vesta’s large southern impact basins, Rheasilvia and Veneneia, lie within or near the Av-1 quadrangle. Therefore it is of particular interest to search for evidence of features of the kind that are found at basin antipodes on other planetary bodies. Albedo markings known as lunar swirls are correlated with basin antipodes and the presence of crustal magnetic anomalies on the Moon, but lighting conditions preclude recognition of such albedo features in images of the antipode of Vesta’s Rheasilvia basin. “Hilly and lineated terrain,” found at the antipodes of large basins on the Moon and Mercury, is not present at the Rheasilvia or Veneneia antipodes. We have identified small-scale linear depressions that may be related to increased fracturing in the Rheasilvia and Veneneia antipodal areas, consistent with impact-induced stresses (Buczkowski, D. et al. [2012b]. Analysis of the large scale troughs on Vesta and correlation to a model of giant impact into a differentiated asteroid. Geol. Soc. of America Annual Meeting. Abstract 152-4; Bowling, T.J. et al. [2013]. J. Geophys. Res. – Planets, 118. http://dx.doi.org/10.1002/jgre.20123). The general high elevation of much of the north polar region could, in part, be a result of uplift caused by the Rheasilvia basin-forming impact, as predicted by numerical modeling (Bowling, T.J. et al. [2013]. J. Geophys. Res. – Planets, 118. http://dx.doi.org/10.1002/jgre.20123). However, stratigraphic and crater size–frequency distribution analysis indicate that the elevated terrain predates the two southern basins and hence is likely a remnant of the ancient vestan crust. The lack of large-scale morphological features at the basin antipodes can be attributed to weakened antipodal constructive interference of seismic waves caused by an oblique impact or by Vesta’s non-spherical shape, or by attenuation of seismic waves because of the physical properties of Vesta’s interior. A first-order analysis of the Dawn global digital elevation model for Vesta indicates that areas of permanent shadow are unlikely to be present in the vicinity of the north pole.

Devil's Slide: An Evolving Feature of California's Coastal Landscape

Coastal landslides in the United States remain a persistent threat to human life and urban development. The focus of this study is a landslide-prone section of the central California coastline, approximately 20 km south of San Francisco, known as Devil9s Slide. This investigation employs an extensive aerial image inventory, digital elevation models (DEMs), and a water balance/limit-equilibrium approach to better understand the spatial and temporal characteristics of deep-seated bedrock slides at the site. Photographic surveys of the area reveal nearly 3 km of headscarp and a complex network of slope failures that respond to hydrologic, seismic, and anthropogenic perturbations. DEM analysis suggests that for a 145-year period (1866 to 2010), the study area experienced an average coastal retreat rate of 0.14 m/yr and an average volumetric loss of 11,216 m 3 /yr. At least 38 percent of the landscape evolution in the steep coastal terrain has been driven by slope failure events. A loosely coupled water balance/limit-equilibrium analysis quantitatively illustrates the precarious nature of the active landslide zone at the site. The slope is shown to be unstable for a large suite of equally likely scenarios. The analyses presented herein suggest that future work should include a rigorous characterization of pore-water pressure development, driven by comprehensive simulations of subsurface hydrologic response, to improve our understanding of slope failure initiation at the Devil9s Slide site.

Accuracy Analysis of Digital Elevation Model Relating to Spatial Resolution and Terrain Slope by Bilinear Interpolation

This study investigates the accuracy analysis of the digital elevation model (DEM) with respect to the following two major factors that strongly affect the interpolated accuracy: (1) spatial resolution of a DEM and (2) terrain slope. Unlike existing studies based mainly on a simulation approach, this research first provides an analytical approach in order to build the relationship between the interpolated DEM accuracy and its influencing factors. The bi-linear interpolation model was adopted to produce this analytic model formalized as inequalities. Then, our analytic models were verified and further rectified by means of experimental studies in order to derive a practical formula for estimating the DEM accuracy together with an optimization model for calculating the required resolution when a prescribed upper bound to the DEM accuracy is given. Moreover, this analytic approach can cope with either a grid-based DEM or a randomly scattered scenario whose efficacies have been validated by the experiments using both synthetic and realistic data sets. In particular, these findings first establish the rules for directly correlating the horizontal resolution of DEM data with vertical accuracy.

Short Communication: TopoToolbox 2 – MATLAB-based software for topographic analysis and modeling in Earth surface sciences

Abstract. TopoToolbox is a MATLAB program for the analysis of digital elevation models (DEMs). With the release of version 2, the software adopts an object-oriented programming (OOP) approach to work with gridded DEMs and derived data such as flow directions and stream networks. The introduction of a novel technique to store flow directions as topologically ordered vectors of indices enables calculation of flow-related attributes such as flow accumulation ∼20 times faster than conventional algorithms while at the same time reducing memory overhead to 33% of that required by the previous version. Graphical user interfaces (GUIs) enable visual exploration and interaction with DEMs and derivatives and provide access to tools targeted at fluvial and tectonic geomorphologists. With its new release, TopoToolbox has become a more memory-efficient and faster tool for basic and advanced digital terrain analysis that can be used as a framework for building hydrological and geomorphological models in MATLAB.

Evaluation of Selected Site Location for Subsurface Dam Construction within Isayi Watershed Using GIS and RS Garmiyan Area, Kurdistan Region

Garmiyan area suffers from many water problems such as poor rainfall rate, water shortage, aridity and absence of groundwater in many places. Hence the subsurface dam is the best solution due to many advantages such as low cost of construction, least maintenance, low evaporation, no contamination, utilization of the land over the dam and better storage. The objective of this study is to evaluate the suitability of the selected site location for subsurface dam construction, to serve as strategic water supply storage, to solute the aridity and water shortage in this area of arid to semi arid climate in Isayi watershed within the stream deposits. Geographic information systems (GIS) and remote sensing through satellite images and Digital Elevation Model (DEM) interpretation and analysis have facilitated the investigation with more accuracy. ArcGIS helped in construction of thematic maps of the studied area. The geologic, structural, geomorphologic, hydrologic and hydrogeologic characteristics with GPR survey show the suitability of the selected site location for construction of subsurface dam. According to the standard water quality for domestic, irrigation and livestock the water quality of all water samples are within the recommended range and the best time to be chosen, for construction of the subsurface dam, is during the autumn season from September to November.

Geophysical analysis of transverse ridges and internal structure at Lone Peak Rock Glacier, Big Sky, Montana, USA

AbstractRock glaciers are periglacial alpine landforms that are found in many locations worldwide. Whereas well-developed models of deformation are established for traditional alpine glaciers, rock glacier deformation is poorly understood. Geophysical data from Lone Peak Rock Glacier (LPRG), southwest Montana, USA, are paired with lidar bare-earth 1 m digital elevation model (DEM) analysis to explore potential genetic relationships between internal composition, structure and regularly spaced arcuate transverse ridges expressed at the rock glacier surface. The internal composition of LPRG is heterogeneous, with frozen debris and clean ice overlain by an unconsolidated talus mantle. Upslope-dipping, clearly distinguished reflectors in the ground-penetrating radar (GPR) longitudinal survey at LPRG correspond to transverse ridges. The spacing and slope of individual features at the surface and in the subsurface were measured and compared and are found to be similar. The structures observed at LPRG and other rock glaciers are similar to structures detected in glaciotectonically altered sediment, ice-cored moraines and other rock glacier settings. This finding suggests that transverse ridges on rock glaciers may be used as geomorphic indicators of internal deformation. This study contributes to the body of research on the application of GPR to rock glaciers, and is the first to directly pair and analyze individual surface topographic features with internal structures.

Spatial characterization of landscapes through multifractal analysis of DEM.

Landscape evolution is driven by abiotic, biotic, and anthropic factors. The interactions among these factors and their influence at different scales create a complex dynamic. Landscapes have been shown to exhibit numerous scaling laws, from Horton's laws to more sophisticated scaling of heights in topography and river network topology. This scaling and multiscaling analysis has the potential to characterise the landscape in terms of the statistical signature of the measure selected. The study zone is a matrix obtained from a digital elevation model (DEM) (map 10 × 10 m, and height 1 m) that corresponds to homogeneous region with respect to soil characteristics and climatology known as “Monte El Pardo” although the water level of a reservoir and the topography play a main role on its organization and evolution. We have investigated whether the multifractal analysis of a DEM shows common features that can be used to reveal the underlying patterns and information associated with the landscape of the DEM mapping and studied the influence of the water level of the reservoir on the applied analysis. The results show that the use of the multifractal approach with mean absolute gradient data is a useful tool for analysing the topography represented by the DEM.

21st-century increase in glacier mass loss in the Wrangell Mountains, Alaska, USA, from airborne laser altimetry and satellite stereo imagery

AbstractAlaskan glaciers are among the largest regional contributors to sea-level rise in the latter half of the 20th century. Earlier studies have documented extensive and accelerated ice wastage in most regions of Alaska. Here we study five decades of mass loss on high-elevation, land-terminating glaciers of the Wrangell Mountains (~ 4900 km2) in central Alaska based on airborne center-line laser altimetry data from 2000 and 2007, a digital elevation model (DEM) from ASTER and SPOT5, and US Geological Survey topographic maps from 1957. The regional mass-balance estimates derived from center-line laser altimetry profiles using two regional extrapolation techniques agree well with that from DEM differencing. Repeat altimetry measurements reveal accelerated mass loss over the Wrangell Mountains, with the regional mass-balance rate evolving from –0.07 ± 0.19 m w.e. a–1 during 1957–2000 to –0.24 ± 0.16 m w.e. a–1 during 2000–07. Nabesna, the largest glacier in this region (˜1056 km2), lost mass four times faster during 2000–07 than during 1957–2000. Although accelerated, the mass change over this region is slower than in other glacierized regions of Alaska, particularly those with tidewater glaciers. Together, our laser altimetry and satellite DEM analyses demonstrate increased wastage of these glaciers during the last 50 years.

How multiple foliations may control large gravitational phenomena: A case study from the Cismon Valley, Eastern Alps, Italy

The right slope of the High Cismon Valley (Trento Province, Italy), carved into the poly-deformed phyllites of the South Alpine Basement, shows evidence of differential Quaternary slope evolution which highly depends on how the slope intersects the inherited structures. In the study area, the regional schistosity outlines a kilometer-scale NNW–SSE trending fold, with close flanks and an axial plane dipping to the NE. The structure obliquely intersects the NNE–SSW trending slope so that the northern part of the slope follows the upper limb of the fold and the southern sector coincides with the lower limb and the hinge. The secondary axial-plane foliation is typically incipient at the fold flanks, and much more pervasive and fan-shaped near the hinge zone. This foliation, as well as the asymmetric polyharmonic secondary folds, has significant consequences on rock mass mechanical properties and on mechanisms and timing of the gravitational phenomena developed along the slope.In particular the Joint Compressive Strength (JCS) and the Geological Strength Index (GSI), obtained on stable outcrops outside the deforming area, display a decrease from north to south. This points to a progressive deterioration of the rock mass strength which directly reflects the influence of the pre-existing fabric. The results obtained by the analysis of LiDAR-derived digital elevation model show evidence of two different gravitational movements, located in the northern and southern sectors of the slope respectively. The northern side is characterized by an ongoing deep-seated gravitational slope deformation (DSGSD) likely triggered by post-glacial unloading, derived from the retreat of the ice tongue that filled the Cismon Valley during the Last Glacial Maximum (LGM). Conversely, the southern part of the slope is the expression of a fully evolved pre-LGM gravitational collapse. This heterogeneous behavior of the slope is most likely controlled by the secondary foliation and asymmetric polyharmonic folds, the former being of paramount importance for the release of the mobilized mass at the crown area, and the latter easing or impeding the downslope movement. Although it is widely accepted that the regional foliation is the dominant controlling factor of DSGSDs on poly-deformed and highly foliated metamorphic basement, our work suggests that the secondary foliation, as well as parasitic folds, may also have remarkable effects on slope evolution if favorably oriented and sufficiently pervasive.

STATISTICAL EVALUATION OF FITTING ACCURACY OF GLOBAL AND LOCAL DIGITAL ELEVATION MODELS IN IRAN

Abstract. Digital Elevation Models (DEMs) are one of the most important data for various applications such as hydrological studies, topography mapping and ortho image generation. There are well-known DEMs of the whole world that represent the terrain's surface at variable resolution and they are also freely available for 99% of the globe. However, it is necessary to assess the quality of the global DEMs for the regional scale applications.These models are evaluated by differencing with other reference DEMs or ground control points (GCPs) in order to estimate the quality and accuracy parameters over different land cover types. In this paper, a comparison of ASTER GDEM ver2, SRTM DEM with more than 800 reference GCPs and also with a local elevation model over the area of Iran is presented. This study investigates DEM’s characteristics such as systematic error (bias), vertical accuracy and outliers for DEMs using both the usual (Mean error, Root Mean Square Error, Standard Deviation) and the robust (Median, Normalized Median Absolute Deviation, Sample Quantiles) descriptors. Also, the visual assessment tools are used to illustrate the quality of DEMs, such as normalized histograms and Q-Q plots. The results of the study confirmed that there is a negative elevation bias of approximately 5 meters of GDEM ver2. The measured RMSE and NMAD for elevation differences of GDEM-GCPs are 7.1 m and 3.2 m, respectively, while these values for SRTM and GCPs are 9.0 m and 4.4 m. On the other hand, in comparison with the local DEM, GDEM ver2 exhibits the RMSE of about 6.7 m, a little higher than the RMSE of SRTM (5.1 m).The results of height difference classification and other statistical analysis of GDEM ver2-local DEM and SRTM-local DEM reveal that SRTM is slightly more accurate than GDEM ver2. Accordingly, SRTM has no noticeable bias and shift from Local DEM and they have more consistency to each other, while GDEM ver2 has always a negative bias.