Reference Digital Elevation Model Research Articles

Assessment of interferometric dems from terrasar‐x stripmap and spotlight stereopairs: case study in istanbul

AbstractTerraSAR‐X (TSX) has led to a new era for synthetic aperture radar (SAR) imaging, offering high‐resolution (1 m) data that was not previously available from space. The TSX X‐band sensor can be operated in three interferometrically compatible imaging modes: Stripmap (SM), high‐resolution Spotlight (HS) and ScanSAR. Due to the low resolution of ScanSAR (16 to 30 m), SM and HS images are preferred for resolution‐based applications. This paper attempts to validate and compare the digital elevation models (DEMs) derived from TSX SM and HS image pairs. Digital surface models (DSMs) were generated by interferometry in a part of Istanbul with a variety of ground types. These DSMs were converted to DEMs by filtering and then compared with a reference DEM produced from aerial photographs. The quality assessment was performed using advanced analyses concerned with accuracy and morphologic detail. The results of both absolute and relative accuracy analyses clearly reveal that the quality of the TSX HS DEM is better than SM and very consistent with the reference model.

Quantitative assessment of remotely sensed global surface models using various land classes produced from Landsat data in Istanbul

Digital elevation model (DEM) is the most popular product for three-dimensional (3D) digital representation of bare Earth surface and can be produced by many techniques with different characteristics and ground sampling distances (GSD). Space-borne optical and synthetic aperture radar (SAR) imaging are two of the most preferred and modern techniques for DEM generation. Using them, global DEMs that cover almost entire Earth are produced with low cost and time saving processing. In this study, we aimed to assess the Satellite pour l’observation de la Terre-5 (SPOT-5), High Resolution Stereoscopic (HRS), the Advanced Space-borne Thermal Emission and Reflection Radiometer (ASTER), and the Shuttle Radar Topography Mission (SRTM) C-band global DEMs, produced with space-borne optical and SAR imaging. For the assessment, a reference DEM derived from 1:1000 scaled digital photogrammetric maps was used. The study is performed in 100 km2 study area in Istanbul including various land classes such as open land, forest, built-up land, scrub and rough terrain obtained from Landsat data. The analyses were realized considering three vertical accuracy types as fundamental, supplemental, and consolidated, defined by national digital elevation program (NDEP) of USA. The results showed that, vertical accuracy of SRTM C-band DEM is better than optical models in all three accuracy types despite having the largest grid spacing. The result of SPOT-5 HRS DEM is very close by SRTM and superior in comparison with ASTER models.

Advanced free-form deformation and Kullback–Lieblier divergence measure for digital elevation model registration

Registration is the process of transforming various images of the same object, place, etc. to confer one coordinate system, be they multimodal, multi-temporal of the same place or images of different places having certain common characteristics. Many methods have been tried for image registration; however, only a handful of methods may be said to work for digital elevation model (DEM) registration. The motivation of the present work is to perform a robust and efficient algorithm to perform Elevation model image registration. In this paper, we present a new approach for DEM registration, particularly for multimodal or multi-temporal DEMs. For time efficient, robust and precise registration of DEMs, a novel idea has been proposed using rational DMS-spline volumes (Xu et al. in J Comput Sci Technol 23(5):862–873, 1996; McDonnell and Qin in J Gr Tools 12(3):24–41, 2007) (the term DMS is acronym for the three authors, namely Dahmen et al. in Math Comput 59(199):97–115, 1997). This is based on the usage of arbitrary topology lattices (MacCracken and Joy in 23rd annual conference on computer graphics and interactive techniques proceedings. ACM-SIGGRAPH, pp 181–188, 1996; Feng et al. in Vis Comput Int Comput Gr 22(1):28–42, 2005). Using free-form deformation has lead to the usage of global and local transformations for registration of candidate image domain to reference image domain. Also, a similarity measure based on Kullback–Leibler divergence (KLD) has been used for measuring robustness of the method so proposed. The task of registration is achieved by minimizing the cost function using rational DMS-spline functions for local registration. After experimentations, the results show that the registration process, of registration of candidate DEM to reference DEM, could be completed successfully. Comparison of similarity measurement methods such as mutual information, correlation coefficient and peak signal-to-noise ratio with that of KLD-based has been performed. Comparative study with existing works suggests that the presented scheme is better, when compared with respect to above mentioned parameters.

A COMPARATIVE ANALYSIS OF DIFFERENT DEM INTERPOLATION METHODS

Visualization of geospatial entities generally entails Digital Elevation models (DEMs) that are interpolated to establish three dimensional co-ordinates for entire terrain. The accuracy of generated terrain model depends on the interpolation mechanism adopted and hence it is needed to investigate the comparative performance of different approaches in this context. General interpolation techniques namely Inverse Distance Weighted, Kriging, Topo to Raster, Natural Neighbor, and Spline approaches have been compared. Differential ground field survey has been conducted to generate reference DEM as well as specific set of test points for comparative evaluation. We have also investigated the suitability SRTM DEM for Indian terrain by comparing it with the SOI DEM. Contours were generated at different intervals for comparative analysis and found SRTM as more suitable. The terrain sensitivity of various methods has also been analyzed with reference to the study area.

DEM Extraction in Urban Areas Using High-Resolution TerraSAR-X Imagery

Three-dimensional (3D) spatial information is crucial for improving the quality of human life through urban planning and management, and it is widely utilized due to its rapid, periodic and inexpensive acquisition. In this context, extraction of digital surface and elevation models (DSM and DEM) is a significant research topic for space-borne optical and synthetic aperture radar (SAR) remote sensing. The DSMs include visible features on the earth’s surface such as vegetation, forest and elevated man-made objects, while DEMs contain only the bare ground. In this paper, using TerraSAR-X (TSX) high resolution Spotlight (HS) images, high-resolution interferometric DEM generation in a part of Istanbul urban area is aimed. This is not an easy task because of SAR imaging problems in complex geometry of urban settlements. The interferometric processing steps for DSM generation were discussed including critical parameters and thresholds to improve the quality of the final product and a 3 m gridded DSM was generated. The DSM-DEM conversion was performed by filtering and the quality of generated DEM was verified against a reference DEM from stereo photogrammetry with 3 m original grid spacing. The achieved root mean square error of height differences (RMSZ) varies from 7.09 to 8.11 m, depending on the terrain slope. The differential DEM, illustrates the height differences between generated DEM and the reference DEM, was generated to show the correlation between height differences and the coherence map. Finally, a perspective view of test area was created draping extracted DEM and a high-resolution IKONOS panchromatic image.

Generation and Validation of High‐Resolution DEMs from Worldview‐2 Stereo Data

AbstractWorldView‐2 (WV‐2), whose panchromatic images have a 0·5 m ground sampling distance (GSD), was launched by DigitalGlobe in 2009. It is the first commercial satellite to offer 8‐band multispectral imagery with 1·8 m resolution. Due to the off‐nadir sensor rotation of WV‐2, it is feasible to obtain stereo coverage. Digital elevation models (DEMs) have been created with three WV‐2 stereopairs of northern Istanbul with different land types and one of these is comprehensively analysed in this study. A reference DEM, developed from large‐scale aerial photogrammetric mapping, together with a lidar DEM and an overlapping neighbouring WV‐2 DEM, are used for validation. The generated WV‐2 DEM reached, after filtering and in open areas, a standard deviation in height of approximately 1·0 GSD. A higher number of discrepancies larger than 4 m exist than would be expected from a normal distribution, influencing the standard deviation more than the normalised median absolute deviation (NMAD).

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.

Extraction of High Resolution DEM from Cartosat-1 Stereo Imagery using Rational Math Model and Its Accuracy Assessment for a Part of Snow Covered NW-Himalaya

This paper reports the experiments carried out for extraction of DEMs from Cartosat-1 stereo imagery using stereo correlation technique for Manali region. The focus of this paper was to assess the accuracy of extracted DEM with respect to DGPS observations, DEM generated from digitized contours of Survey of India (SoI), 1:50,000 scale topographic map(converted to ellipsoidal height using egm2008 geoid model) as well as well-known freely available DEMs ASTER GDEM and SRTM. The vertical accuracy of Cartosat-1 DEMs was analysed with DGPS derived ground control points. The relative vertical accuracy (root mean square error; RMSE) of Cartosat-1 DEM with DGPS control points was ±9.6 m. The RMSE with the topographic DEM was found to be ±10.6 for 22 spot heights and ±10.8 m for 6,458,800 checkpoints. The relative vertical accuracy assessment is more important than the absolute vertical accuracy assessment. The result of relative accuracy assessment of DEMs with respect to field measurement of DGPS points and reference DEMs shows Cartosat-1 DEM is more accurate when compared to ASTER DEM, SoI Topographic DEM, and SRTM DEM for Manali region.

Assimilation of DEMs Generated from Optical Stereo and InSAR Pair through Data Fusion

Main objective of this study is to compare and assimilate the digital elevation models (DEMs) generated using C-band Envisat, L-band ALOS PALSAR Interferometric SAR (InSAR) datasets and Cartosat-1 optical stereo data. The study area is Dehradun city and surroundings including lower Shivalik hills i.e. the younger Himalayas in the south and higher Himalayas on the north. The general elevation of the area ranges from 400m to 2000m AMSL. Ground control points (GCPs) collected from Differential Global Positioning System (DGPS) survey, were used for satellite triangulation of optical data & geocoding of InSAR data. RMSE for satellite triangulation for cartosat-1 is 0.745 using 6 ground control points and 3 check points. It is found that when GCP’s are used along with reference DEM (SRTM), the DSM generated by ALOS PALSAR and DSM generated from Cartosat-1 stereo data are well representing the terrain. The fusion of imagery from multiple sensors has been in use in remote sensing for scientific exploration in the past but there is a little work done on data fusion application for generation of topography (DEM) through Optical stereo and SAR interferometry data sources. The defined framework for data fusion uses three fundamental steps in the analysis of the system namely, identification, estimation, and validation for algorithm preparation. The knowledge of the study area, i.e. the field, and the processes involved in the DEM generation of optical and InSAR data are cognitively used for rule-based decision making in the algorithm for mathematical generation of resultant DEM through data fusion implemented at feature level.

Digital elevation model (DEM) generation using the SAR interferometry technique

The development of satellite technology is rapidly increasing the evolution of remote sensing. Satellite images give extensive useful information about the land structure that is easily manageable in the process of generating true, high-speed information which allows the forecasting of future environmental and urban planning. Remote sensing comprises active and passive systems. Passive sensors detect natural radiation that is emitted or reflected by the object or surrounding area being observed. Active systems which produce their own electromagnetic energy and their main properties are their ability of collecting data in nearly all atmospheric conditions, day or night. These systems are frequently used to generate a digital elevation model (DEM) because they cover large areas. DEM supplies essential data for applications that are concerned with the Earth’s surface and DEMs derived from survey data are accurate but very expensive and time consuming to create. However, the use of satellite remote sensing to provide images to generate a DEM is considered to be an efficient method of obtaining data. Interferometric Synthetic Aperture Radar (InSAR) is a new geodetic technique for determining earth topography. InSAR measurements are highly dense and they only give information in Line of Sight of Radar. In the study, interferograms were produced from the InSAR images taken by ERS satellites in 1992 and 2007 and we developed the methods to generate a DEM using the InSAR technique and present the results relating to Kayseri Province in Turkey. The accuracy of the DEM derived from the InSAR technique is evaluated in comparison with a reference DEM generated from contours in a topographical map.

Evaluating Shuttle radar and interpolated DEMs for slope gradient and soil erosion estimation in low relief terrain

The error in slope gradient estimates provided by digital elevation models propagates to spatial modelling of erosion and other environmental attributes, potentially impacting land management priorities. This study compared the slope estimates of Shuttle Radar Topographic Mission (SRTM) DEMs with those generated by interpolation of topographic contours, at two grid cell resolutions. The magnitude and spatial patterns of error in DEM slope, and derived erosion estimates using the Revised Universal Soil Loss Equation (RUSLE), were evaluated at three sites in eastern Australia. The sites have low-relief terrain and slope gradients less than 15%, characteristics which dominate the global land surface by area and are often highly utilised. Relative to a reference DEM resampled to the same resolution (a measure of DEM ‘quality’), the 90 m (3-s) SRTM DEM provided the best estimates of slopes, being within 20% for each 5% slope class outside alluvial floodplains where it over-predicted by up to 220%. Relative to a hillslope scale 10 m reference DEM, the 30 m (1-s) SRTM-derived DEM-S, provided slope gradient estimates slightly less biased towards under-prediction than the 90 m SRTM and significantly less biased on alluvial floodplains. In contrast, the 20 m vertical contour intervals underpinning the interpolated DEMs resulted in under-prediction of slope gradient by more than a factor of 5 over large contiguous areas (>1 km2). The 30 m DEM-S product provided the best estimate of hillslope erosion, being 3–4% better than the 90 m SRTM. The slope errors in the interpolated DEMs translated into generally poorer and less consistent erosion estimates than SRTM. From this study it is concluded that the SRTM DEM products, in particular the 30 m SRTM-derived DEM-S, provide estimates of slope gradient and erosion which are more accurate, and more consistent within and between low relief study sites, than interpolated DEMs.

QUANTITATIVE ASSESSMENT OF DIGITAL TOPOGRAPHIC DATA FROM DIFFERENT SOURCES

Abstract. This study includes the quantitative assessment of digital topographic data of the terrain from photogrammetric methods, satellite imaging and RADAR techniques in test side in Istanbul. The side area covers 10 × 10 km2 and includes five different land cover types. The 3 m sampled DEM, which was produced by 1/1000 scaled photogrammetric maps is used as reference and tested against the 94 Ground Control Points (GCP). The 5 m and 30 spacing DEMs derived from 1/5000 scaled photogrammetric maps are used as test data sets as well as 20 m spacing SPOT DEM and 80 m spacing ASTER DEM. Besides, 90 m spacing DEM generated from InSAR technique with SRTM mission was also used as test data. The quantitative assessment of all DEMs were performed and reported based on FEMA and NDEP specifications. The quantitative assessment was carried out for open terrain (%19), forest (%15), built-up areas (%32), scrub and bushes (%26), and rough terrain (%8). The accuracy assessment and quality analyses had been conducted for each terrain classes to reflect the quality with more suitable approach. The 3 m spacing reference DEM is tested against the 94 GCP and obtained Root Mean Square Error (RMSE) for Z was in the range of 0.85 m (open terrain) to 1.94 m (rough terrain) for different terrain classes and 1.45 m using all terrain classes. The more than 20 GCP was available for each terrain classes for quantitative assessment of DEMs. As a result of quantitative assessment, RMSE Z of tested DEMs from photogrammetric methods, satellite imaging and RADAR techniques were computed for each land cover types based on international standards. It is no surprise that, the DEM from photogrammetry were more accurate than the DEM from satellite imaging (SPOT, ASTER) and RADAR (SRTM). As expected, open terrains have better results than the other classes like forest, scrub, built-up and rough terrain for all DEMs. The accomplished results of the quantitative assessment demonstrated the importance of the data source, resolution, and production methods of DEMs. The terrain class is important factor and can not be disregarded in quantitative assessment of digital topographic data.

A New Two-Step Robust Surface Matching Approach for Three-Dimensional Georeferencing of Historical Digital Elevation Models

In this letter, a new approach based on a two-step (coarse and fine) automatic surface matching for registering two overlapping multidate digital elevation models (DEMs) is proposed to avoid the costly and time-consuming ground-control-point acquisition. The proposed methodology was tested to georeference a historical grid DEM obtained from a photogrammetric flight taken in 1977 and located at a heavily developed coastal area of Almería (southeast Spain). The reference DEM consisted of a newer DEM produced by the Andalusia Regional Government from a photogrammetric flight taken in 2001. The results obtained from this work may be deemed as very promising, showing high efficiency and accuracy for historical-DEM georeferencing. The vertical accuracy of the finally coregistered DEM was computed over a recent LiDAR-derived DEM (validation data set) which presented relatively unaltered areas, yielding a standard deviation that is fairly similar to the estimated uncertainty of the reference DEM.

Operational TanDEM-X DEM calibration and first validation results

In June 2010, the German TanDEM-X satellite was launched. Together with its twin satellite TerraSAR-X it flies in a close formation enabling single-pass SAR interferometry. The primary goal of the TanDEM-X mission is the derivation of a global digital elevation model (DEM) with unprecedented global accuracies of 10m in absolute and 2m in relative height. A significant calibration effort is required to achieve this high quality world-wide. In spite of an intensive instrument calibration and a highly accurate orbit and baseline determination, some systematic height errors like offsets and tilts in the order of some meters remain in the interferometric DEMs and have to be determined and removed during the TanDEM-X DEM calibration. The objective of this article is the presentation of an approach for the estimation of correction parameters for remaining systematic height errors applicable to interferometric height models. The approach is based on a least-squares block adjustment using the elevation of ICESat GLA14 data as ground control points and connecting points of adjacent, overlapping DEMs as tie-points. In the first part its implementation in DLR’s ground segment is outlined. In the second part the approach is applied and validated for two of the first TanDEM-X DEM test sites. Therefore, independent reference data, in particular high resolution reference DEMs and GPS tracks, are used. The results show that the absolute height errors of the TanDEM-X DEM are small in these cases, mostly in the order of 1–2m. An additional benefit of the proposed block adjustment method is that it improves the relative accuracy of adjacent DEMs.

A Study of Decadal Sedimentation Trend Changes by Waterline Comparisons within the Ganghwa Tidal Flats Initiated by Human Activities

Abstract This study presents results of a human impact investigation of large-scale construction projects on sedimentation trend and morphologic changes in the Ganghwa tidal flats over 10 years using time-series waterlines from Landsat thematic mapper/enhanced thematic mapper. Waterlines were extracted from remotely sensed images. These images are useful for studying changes in coastlines and tidal flat topography. A reference digital elevation model (DEM) was constructed; then actual waterlines from satellite images were compared with modeled waterlines from the reference DEM. Systematic comparison with respect to horizontal differences between the two waterlines provided information on local conditions of sediment trends within the study area. Seaward or landward migration of waterlines was a clear indication of the change in sedimentation pattern. Deposition has been dominant at the main channel between the southern Ganghwa and the Yeongjong tidal flats, whereas erosion has been dominant at the eastern...

DEM matching for bias compensation of rigorous pushbroom sensor models

DEM matching is a technique to match two surfaces or two DEMs, at different reference frames. It was originally proposed to replace the need of ground control points for absolute orientation of perspective images. This paper examines DEM matching for precise mapping of pushbroom images without ground control points. We proved that DEM matching based on 3D similarity transformation can be used when model errors are only on the platform’s position and attitude biases. We also proposed how to estimate bias errors and how to update rigorous pushbroom sensor models from DEM matching results. We used a SPOT-5 stereo pair at ground sampling distance of 2.5 m and a reference DEM dataset at grid spacing of 30 m and showed that rigorous pushbroom models with accuracy better than twice of the ground sampling distance both in image and object space have been achieved through DEM matching. We showed further that DEM matching based on 3D similarity transformation may not work for pushbroom images with drift or drift rate errors. We discussed the effects of DEM outliers on DEM matching and automated removal of outliers. The major contribution of this paper is that we validate DEM matching, theoretically and experimentally, for estimating position and attitude biases and for establishing rigorous sensor models for pushbroom images.

An evaluation of the accuracy of the ASTER GDEM and the role of stack number: a case study of Nisiros Island, Greece

A reference digital elevation model (RDEM) produced by the Hellenic Military Geographical Service (HMGS) (Athens, Greece) is used to assess the vertical accuracy of the ASTER (advanced spaceborne thermal emission and reflection radiometer) global digital elevation model (GDEM) for a small volcanic island, Nisiros, in south-east Greece. The overall vertical accuracy of the GDEM is within the root mean square error (RMSE) specified by the ASTER DEM Working Group. Despite this, ASTER GDEM is a product with variable vertical accuracy depending on the number of scenes (stack number (SN)) per grid point used for the computation of elevation. The exposure (SN) of a physiographic region to ASTER sensors seems to be elevation- and slope-dependent in this particular study area. The difference between the GDEM and RDEM may partly be explained by the fact that GDEM is a digital surface model and thus the variable landcover heights introduce additional error in accuracy estimates.

Optimization of interpolation parameters when deriving DEM from contour lines

Digital elevation models (DEMs) are still an important and current source of information for digital soil mapping and the modeling of soil processes. The grid DEM is often interpolated from contour lines. The contour sampling step becomes an additional interpolation parameter which can play an important role. The objective of this paper is to optimize the interpolation parameters of the Regularized spline with tension (RST) method, in order to prepare a DEM suitable as an input for erosion modeling. Two contrasting cases, with and without a reference DEM, were investigated. If a reference DEM was available, good results of interpolation were reached both by small and larger sampling steps. In the second case, it was found that small sampling steps should be avoided. The influence of the sampling was demonstrated by topographic potential for erosion and deposition.

SRTM DEM을 이용한 SPOT-5 DEM의 조정 비교

It is necessary to register precisely Digital Elevation Model (DEM) generated from SPOT -5 stereo images in order to monitor the topographic and environmental changes of important topographic features such as Mt. Baekdu. The SPOT-5 DEM is registered taking SRTM DEM as a reference DEM. If SPOT-5 DEM is transformed with single 3D rigid equation, it has many errors. Therefore, this study extracted uniformly ground control points over study area and estimated locally adapted transformation equation. The accuracy of proposed method was evaluated with comparison to scale-based and GCP-based transformation method.

Global Assessment of the New ASTER Global Digital Elevation Model

In 2009, the US National Aeronautics and Space Administration and Japan’s Ministry of Economy, Trade and Industry released a new global digital elevation model (GDEM) derived from reprocessed Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data from the Terra satellite. An initial, empirical assessment of the accuracy and characteristics of the GDEM was carried out using a globally-distributed sample dataset. Statistical and visual analyses of the GDEM, using known reference DEMs and ground control points (GCPs) for comparison, revealed a systematic bias in the ASTER GDEM elevations, higher average noise levels, and a lower effective ground resolution compared to the reference data, as well as numerous topo-graphic artifacts and anomalies. The GDEM appears to meet its accuracy specifications when compared to the reference DEMs, but compared to the GCPs, some of the areas are questionable. In areas that lack good quality terrain data, the GDEM may prove useful, but must be used with care.