TanDEM-X Elevation Research Articles

Biomass Change Estimated by TanDEM-X Interferometry and GEDI in a Tanzanian Forest

Mapping and quantification of forest biomass change are key for forest management and for forests’ contribution to the global carbon budget. We explored the potential of covering this with repeated acquisitions with TanDEM-X. We used an eight-year period in a Tanzanian miombo woodland as a test case, having repeated TanDEM-X elevation data for this period and repeated field inventory data. We also investigated the use of GEDI space–LiDAR footprint AGB estimates as an alternative to field inventory. The map of TanDEM-X elevation change appeared to be an accurate representation of the geography of forest biomass change. The relationship between TanDEM-X phase height and above-ground biomass (AGB) could be represented as a straight line passing through the origin, and this relationship was the same at both the beginning and end of the period. We obtained a similar relationship when we replaced field plot data with the GEDI data. In conclusion, temporal change in miombo woodland biomass is closely related to change in InSAR elevation, and this enabled both an accurate mapping and quantification wall to wall within 5–10% error margins. The combination of TanDEM-X and GEDI may have a near-global potential for estimation of temporal change in forest biomass.

A Multi-Method Approach to Flood Mapping: Reconstructing Inundation Changes in the Cambodian Upper Mekong Delta

As in many tropical deltas globally, annual floods shape the livelihoods of the largely rural population in the Cambodian Mekong delta. Agricultural cycles are keyed to the flood arrival, peak, and recession, and fish populations depend on inundated floodplains for their regeneration. However, as factors like climate change and hydropower infrastructure development are altering the Mekong’s hydrology, the inundation dynamics of its deltaic floodplains are shifting as well. Several studies have assessed the general changes of river discharge and flood extent on a basin- or delta-wide scale. Yet the sustainable development of this region is relying on dynamics at more local and specific scales, which have not been addressed so far.This paper presents a methodology to track the evolution of hydrological regimes and associated inundations in tropical deltas such as the upper Mekong delta in Cambodia, where it is applied over the past 30 years. Data scarcity and heterogeneity of the environment in this region necessitated the use of combined approaches. We established a link between water levels measured in situ and flood maps derived from optical and radar satellite images (Sentinel-1 and −2).The robustness of the link was assessed using Sentinel, Landsat imagery and the TanDEM-X (12 m) elevation model. This water level-flood link (WAFL) was then used to reconstruct a daily time series of inundation extents reaching back to the beginning of hydrological measurements in 1991 (30 years). On this basis, changes in the incidence, duration, and spatial distribution of floods were analysed.The results indicated that WAFL can be used to reconstruct inundation maps with an overall robustness of 87% in comparison to historical inundation maps derived from remote sensing imagery. Comparisons of WAFL-derived flood extents with Landsat images further underscored the significant role of local infrastructure, sedimentation dynamics, and land cover to explain changes in inundation dynamics. WAFL-based analyses revealed that inundation durations have decreased by an average of 19 days when comparing the periods before and after 2008, which was identified as a break point in the hydrological time series. Furthermore, a drastic decrease in inundation the annual frequency with which individual pixels are flooded can be detected during the first half of the traditional flood season, with an average of −21% in early August, negatively impacting water-based livelihoods, from agriculture to fisheries.

Applicability of the global TanDEM-X elevation data for terrain modelling of a forested karst area: a case study from Slovak Karst

New interferometric radar data of the TanDEM-X space mission have become recently available as a global digital elevation model providing 0.4 arc second spatial resolution (ca. 12 meters). The TanDEM-X dataset brings new options into geoscientific research across multiple scales. However, the accuracy and suitability of this data have not been evaluated in such an extensive manner as, for example, the widely used SRTM data which resolution is 1 arc second (ca. 30 m). We present a validation of the vertical accuracy of TanDEM-X DEM product and an evaluation of its suitability for landform classification in a forested karst area. The DEM segmentation using geomorphons was used for the automated object-based landform classification. We focused on the identification of dolines for which polygons of dolines mapped by an expert-driven approach were used for validation. Airborne lidar data in the form of DSM and DTM were used as the reference dataset for validation of the TanDEM-X DEM vertical accuracy. The results from the study area show that the vertical RMSE of the TanDEM-X data is 3.42 m with respect to the lidar DSM and 9.64 m in comparison with lidar DTM. The identification of dolines by the geomorphon approach achieved 73 % with TanDEM-X, lower than for the lidar DTM (85 %). The TanDEM-X elevation errors were strongly correlated with the canopy height derived from the lidar data suggesting limited suitability of the TanDEM-X data for mapping fine-scale geomorphological features under forests while there was a good match with the lidar DTM terrain in open areas. URL: https://www.gcass.science.upjs.sk/

Investigating the bias of TanDEM-X digital elevation models of glaciers on the Tibetan Plateau: impacting factors and potential effects on geodetic mass-balance measurements

Abstract The TanDEM-X DEM is a valuable data source for estimating glacier mass balance. However, the accuracy of TanDEM-X elevation over glaciers can be affected by microwave penetration and phase decorrelation. To investigate the bias of TanDEM-X DEMs of glaciers on the Tibetan Plateau, these DEMs were subtracted from SPOT-6 DEMs obtained around the same time at two study sites. The average bias over the studied glacier areas in West Kunlun (175.0 km2) was 2.106 ± 0.012 m in April 2014, and it was 1.523 ± 0.011 m in Geladandong (228.8 km2) in October 2013. By combining backscatter coefficients and interferometric coherence maps, we found surface decorrelation and baseline decorrelation can cause obvious bias in addition to microwave penetration. If the optical/laser data and winter TanDEM-X data were used as new and historic elevation sources for mass-balance measurements over an arbitrary observation period of 10 years, the glacier mass loss rates in West Kunlun and Geladandong would be potentially underestimated by 0.218 ± 0.016 and 0.158 ± 0.011 m w.e. a−1, respectively. The impact is therefore significant, and users should carefully treat the bias of TanDEM-X DEMs when retrieving a geodetic glacier mass balance.

GNSS mobile road dam surveying for TanDEM-X correction to improve the database for floodwater modeling in northern Namibia

The aim of this study is the improvement of the TanDEM-X elevation model for future floodwater modeling by implementing surveyed road dams and the use of filter algorithms. Modern satellite systems like TanDEM-X deliver high-resolution images with a high vertical and horizontal accuracy. Nevertheless, regarding special usage they sometimes reach their limits in documenting important features that are smaller than the grid size. Especially in the context of 2D-hydrodynamic flood modelling, the features that influence the runoff processes, e.g. road dams and culverts, have to be included for precise calculations. To fulfil the objective, the main road dams were surveyed, especially those that are blocking the flood water flowing from south Angola to the Etosha Pan in northern Namibia. First, a Leica GS 16 Sensor was installed on the roof of a car recording position data in real time while driving on the road dams in the Cuvelai Basin. In total, 532 km of road dams have been investigated during 4 days while driving at a top speed of 80 km/h. Due to the long driving distances, the daily regular adjustment of the base station would have been necessary but logistically not possible. Moreover, the lack of reference stations made a RTK and Network-RTK solution likewise impossible. For that reasons, the Leica SmartLink function was used. This method is not dependent on classic reference stations next to the GNSS sensor but instead works with geostationary satellites sending correction data in real time. The surveyed road dam elevation data have a vertical accuracy of 4.3 cm up to 10 cm. These precise measurements contribute to rectifying the TanDEM-X elevation data and thus improve the surface runoff network for the future floodwater model and should enhance the floodwater prediction for the Cuvelai Basin.

Evaluation of topographic correction methods for LULC preparation based on multi-source DEMs and Landsat-8 imagery

Topographic shadows of irregular mountains obstruct the analysis of satellite images in hilly areas. Due to this effect, there is high variability in the reflectance response of similar vegetation types, i.e. sunny areas show more than actual reflectance, whereas shaded areas show less than expected reflectance. In this study, we have evaluated the performance of five topographic correction methods, namely Cosine, C-Huang Wei, semi empirical C, SCS + C and Variable Empirical Coefficient Algorithm (VECA) depending on the solar incidence angle and exitance angle. The two well-known digital elevation models (DEM) i.e. Shuttle Radar Topography Mission (SRTM) and TanDEM-X have been used for the study. The efficiency of the correction methods is assessed on Landsat-8 satellite image using three criteria: visual interpretation, statistical assessment and classification accuracy assessment. As seen from the statistical analysis, VECA and C-correction method provides good correction of topography for both SRTM and TanDEM-X elevation models. We have used support vector machine (SVM) classifier for classification of topographically corrected images. Our results show that VECA and C-correction method increased classification accuracy from 65.60% (for uncorrected image) to 82.40% for SRTM and 64.00% to 80.00% for TanDEM-X respectively. The highest accuracy of classification is obtained using VECA/C method with SRTM DEM. However, the SCS + C-correction method impressively reduced the visual topography effects.

Fusion of TanDEM-X and Cartosat-1 elevation data supported by neural network-predicted weight maps

Recently, the bistatic SAR interferometry mission TanDEM-X provided a global terrain map with unprecedented accuracy. However, visual inspection and empirical assessment of TanDEM-X elevation data against high-resolution ground truth illustrates that the quality of the DEM decreases in urban areas because of SAR-inherent imaging properties. One possible solution for an enhancement of the TanDEM-X DEM quality is to fuse it with other elevation data derived from high-resolution optical stereoscopic imagery, such as that provided by the Cartosat-1 mission. This is usually done by Weighted Averaging (WA) of previously aligned DEM cells. The main contribution of this paper is to develop a method to efficiently predict weight maps in order to achieve optimized fusion results. The prediction is modeled using a fully connected Artificial Neural Network (ANN). The idea of this ANN is to extract suitable features from DEMs that relate to height residuals in training areas and then to automatically learn the pattern of the relationship between height errors and features. The results show the DEM fusion based on the ANN-predicted weights improves the qualities of the study DEMs. Apart from increasing the absolute accuracy of Cartosat-1 DEM by DEM fusion, the relative accuracy (respective to reference LiDAR data) of DEMs is improved by up to 50% in urban areas and 22% in non-urban areas while the improvement by the HEM-based method does not exceed 20% and 10% in urban and non-urban areas respectively.

Elevation change of Fedchenko Glacier, Pamir Mountains, from GNSS field measurements and TanDEM-X elevation models, with a focus on the upper glacier

ABSTRACTFedchenko Glacier experienced a large thickness loss since the first scientific investigations in 1928. As the largest glacier in the Pamir Mountains, this glacier plays an important role for the regional glacier mass budget. We use a series of Global Navigation Satellite Systems observations from 2009 to 2016 and TanDEM-X elevation models from 2011 to 2016 to investigate recent elevation changes. Accounting for radar wave penetration minimizes biases in elevation that can otherwise reach up to 6 m in dry snow on Fedchenko Glacier, with mean values of 3–4 m in the high accumulation regions. The seasonal elevation changes reach up to ±5 m. The glacier surface elevation decreased along its entire length over multi-year periods. Thinning rates increased between 2000 and 2016 by a factor of 1.8 compared with 1928–2000, resulting in peak values of 1.5 m a−1. Even the highest accumulation basins above 5000 m elevation have been affected by glacier thinning with change rates between −0.2 and −0.4 m a−1 from 2009 to 2016. The estimated glacier-wide mass-balance rates are −0.27 ± 0.05 m w.e. a−1 for 2000 to 2011 and −0.51 ± 0.04 m w.e. a−1 between 2011 and 2016.

Which DEM is best for analyzing fluvial landscape development in mountainous terrains?

Regional studies of fluvial landforms and long-term (Quaternary) landscape development in remote mountain landscapes routinely use satellite-derived DEM data sets. The SRTM and ASTER DEMs are the most commonly utilised because of their longer availability, free cost, and ease of access. However, rapid technological developments mean that newer and higher resolution DEM data sets such as ALOS World 3D (AW3D) and TanDEM-X are being released to the scientific community. Geomorphologists are thus faced with an increasingly problematic challenge of selecting an appropriate DEM for their landscape analyses. Here, we test the application of four medium resolution DEM products (30m=SRTM, ASTER, AW3D; 12m=TanDEM-X) for qualitative and quantitative analysis of a fluvial mountain landscape using the Dades River catchment (High Atlas Mountains, Morocco). This landscape comprises significant DEM remote sensing challenges, notably a high mountain relief, steep slopes, and a deeply incised high sinuosity drainage network with narrow canyon/gorge reaches. Our goal was to see which DEM produced the most representative best fit drainage network and meaningful quantification. To achieve this, we used ArcGIS and Stream Profiler platforms to generate catchment hillshade and slope rasters and to extract drainage network, channel long profile and channel slope, and area data. TanDEM-X produces the clearest landscape representation but with channel routing errors in localised high relief areas. Thirty-metre DEMs are smoother and less detailed, but the AW3D shows the closest fit to the real drainage network configuration. The TanDEM-X elevation values are the closest to field-derived GPS measurements. Long profiles exhibit similar shapes but with minor differences in length, elevation, and the degree of noise/smoothing, with AW3D producing the best representation. Slope-area plots display similarly positioned slope-break knickpoints with modest differences in steepness and concavity indices, but again best represented by AW3D. Collectively, our study shows that despite the higher effective resolution of TanDEM-X (12m), the AW3D (30m) data performs strongly across all analyses suggesting that it currently offers the greatest potential for regional mountain geomorphological analyses.

Identification of historic landscape features and settlement mounds in the Western Nile Delta by means of remote sensing time series analysis and the evaluation of vegetation characteristics

Remote sensing techniques gain increasing importance in landscape archaeological research. Traditional archaeological excavation techniques are slow and time in the Nile Delta is running out. The Nile Delta has been settled and used for agricultural cultivation since the Neolithic period and is shaped by the interplay of urbanization and agriculture. In particular, the study of ancient settlement mounds (tells) and landscape archaeological features such as former river channels requires urgent action. This study seeks to develop supervised classification techniques on the basis of multitemporal Landsat 8 images to easily monitor existing high tells in the Delta that have not been destroyed yet. In the 19th and early 20th centuries many tells were destroyed, because tell sediments (sebakh) were harvested on an industrial scale in order to be used as fertilizer. These activities continued on a smaller scale into the mid to later 20th century. Geochemical analysis of ancient settlement material (sebakh) has confirmed the high content of nutrients. In a second step which is based on these geochemical findings, we seek to identify the category of lost tells which had been transformed into agricultural areas. We suggest that the presence of ancient settlement material enhances the overall vegetation performance and indirectly allows identification of lost tells via describing the vegetation performance. In general, the vegetation performance is a new measure and invented within this study. It is calculated as the product of different measures describing the plant growth, namely the mean NDVI (Normalized Difference Vegetation Index), growth statistics and crop rotations derived from a large set of multitemporal NDVI images. Our results show that there exists a relationship between vegetation performance and the appearance of archaeological material in the topsoil and such information can be useful for planning of non-invasive archaeological surveys. Remarkably the vegetation performance corresponds with the location of former Nile branches that are currently investigated by the authors on the basis of TandemX elevation data and sedimentological investigations of the area. Several factors such as water availability and salinity also affect plant growth and mask this relationship. Additionally, our methods to describe the number of crop rotations or growth statistics from NDVI time series help to analyse the agricultural areas in the Nile Delta. Therefore, the methods used in this study may offer important insights on aspects of urban sprawl and agricultural areas in the Nile Delta and beyond.

UNCERTAINTY ASSESSMENT AND WEIGHT MAP GENERATION FOR EFFICIENT FUSION OF TANDEM-X AND CARTOSAT-1 DEMS

Abstract. Recently, with InSAR data provided by the German TanDEM-X mission, a new global, high-resolution Digital Elevation Model (DEM) has been produced by the German Aerospace Center (DLR) with unprecedented height accuracy. However, due to SAR-inherent sensor specifics, its quality decreases over urban areas, making additional improvement necessary. On the other hand, DEMs derived from optical remote sensing imagery, such as Cartosat-1 data, have an apparently greater resolution in urban areas, making their fusion with TanDEM-X elevation data a promising perspective. The objective of this paper is two-fold: First, the height accuracies of TanDEM-X and Cartosat-1 elevation data over different land types are empirically evaluated in order to analyze the potential of TanDEM-XCartosat- 1 DEM data fusion. After the quality assessment, urban DEM fusion using weighted averaging is investigated. In this experiment, both weight maps derived from the height error maps delivered with the DEM data, as well as more sophisticated weight maps predicted by a procedure based on artificial neural networks (ANNs) are compared. The ANN framework employs several features that can describe the height residual performance to predict the weights used in the subsequent fusion step. The results demonstrate that especially the ANN-based framework is able to improve the quality of the final DEM through data fusion.

Surge dynamics and lake outbursts of Kyagar Glacier, Karakoram

Abstract. The recent surge cycle of Kyagar Glacier, in the Chinese Karakoram, caused formation of an ice-dammed lake and subsequent glacial lake outburst floods (GLOFs) exceeding 40 million m3 in 2015 and 2016. GLOFs from Kyagar Glacier reached double this size in 2002 and earlier, but the role of glacier surging in GLOF formation was previously unrecognised. We present an integrative analysis of the glacier surge dynamics from 2011 to 2016, assessing surge mechanisms and evaluating the surge cycle impact on GLOFs. Over 80 glacier surface velocity fields were created from TanDEM-X (TerraSAR-X add-on for Digital Elevation Measurement), Sentinel-1A, and Landsat satellite data. Changes in ice thickness distribution were revealed by a time series of TanDEM-X elevation models. The analysis shows that, during a quiescence phase lasting at least 14 years, ice mass built up in a reservoir area at the top of the glacier tongue, and the terminus thinned by up to 100 m, but in the 2 years preceding the surge onset this pattern reversed. The surge initiated with the onset of the 2014 melt season, and in the following 15 months velocity evolved in a manner consistent with a hydrologically controlled surge mechanism. Dramatic accelerations coincided with melt seasons, winter deceleration was accompanied by subglacial drainage, and rapid surge termination occurred following the 2015 GLOF. Rapid basal motion during the surge is seemingly controlled by high water pressure, caused by input of surface water into either an inefficient subglacial drainage system or unstable subglacial till. The potential lake volume increased to more than 70 million m3 by late 2016, as a result of over 60 m of thickening at the terminus. Lake formation and the evolution of the ice dam height should be carefully monitored through remote sensing to anticipate large GLOFs in the near future.

Recent slowdown and thinning of debris-covered glaciers in south-eastern Tibet

Recent large-scale remote sensing studies have shown that glacier mass loss in south-eastern Tibet, specifically in the eastern Nyainqêntanglha Range exceeds the average in High Asia. However, detailed studies at individual glaciers are scarce and the drivers behind the observed changes are poorly constrained to date. Employing feature tracking techniques on TerraSAR-X data for the periods 2008/2009, 2012/2013 and 2013/2014 we found measurable surface velocities through to the glacier terminus positions of five debris-covered glacier tongues. This is contrary to debris-covered glaciers in other parts of High Asia, where stagnant glacier tongues are common. Our feature tracking results for the 2013/2014 period suggest an average deceleration of 51% when compared with published Landsat velocities for the period 1999/2003. Further, we estimated surface elevation changes for the five glaciers from recently released one arc second resolution elevation data obtained during the Shuttle Radar Topography Mission in 2000 and an interferometrical derived TanDEM-X elevation model for the year 2014. With an average rate of −0.83 ± 0.57 m a−1 we confirm strong surface lowering in the region, despite the widely discussed insulation effect of debris cover. Beside the influence of thermokarst processes and delayed response times of debris-covered glaciers, we highlight that abundant monsoonal summer rainfall might contribute significantly to the pronounced negative mass balances in the study region.

TanDEM-X elevation model data for canopy height and aboveground biomass retrieval in a tropical peat swamp forest

ABSTRACTIt was demonstrated in the past that radar data is useful to estimate aboveground biomass due to their interferometric capability. Therefore, the potential of a globally available TanDEM-X digital elevation model (DEM) was investigated for aboveground biomass estimation via canopy height models (CHMs) in a tropical peat swamp forest. However, CHMs based on X-band interferometers usually require external terrain models. High accurate terrain models are not available on global scale. Therefore, an approach exclusively based on TanDEM-X and the decrease of accuracy compared to an approach utilizing a high accurate terrain model is assessed. In addition, the potential of X-band interferometric heights in tropical forests needs to be evaluated. Therefore, two CHMs were derived from an intermediate TanDEM-X DEM (iDEM; as a precursor for WorldDEMTM) alone and in combination with lidar measurements used as terrain model. The analysis showed high accuracies (root mean square error [RMSE] = 5 m) for CHMs based on iDEM and reliable estimation of aboveground biomass. The iDEM CHM, exclusively based on TanDEM-X, achieved a poor R2 of 0.2, nonetheless resulted in a cross-validated RMSE of 54 t ha−1 (16%). The low R2 suggested that the X-band height alone was not sufficient to estimate an accurate CHM, and thus the need for external terrain models was confirmed. A CHM retrieved from the difference of iDEM and an accurate lidar terrain model achieved a considerably higher correlation with aboveground biomass (R2 = 0.68) and low cross-validated RMSE of 24.5 t ha−1 (7.5%). This was higher or comparable to other aboveground biomass estimations in tropical peat swamp forests. The potential of X-band interferometric heights for CHM and biomass estimation was thus confirmed in tropical forest in addition to existing knowledge in boreal forests.

Evaluation of intermediate TanDEM-X digital elevation data products over Tasmania using other digital elevation models and accurate heights from the Australian National Gravity Database

ABSTRACTThe successful operation of the TanDEM-X satellite mission is the start of a new era of globally consistent and accurate digital elevation data for planet Earth. In this work available 12 m-resolution intermediate TanDEM-X products (DEM: digital elevation model; HEM: height error map; COV: coverage map; WAM: water indication mask) are evaluated over Tasmania. Elevations from the TanDEM-X intermediate digital elevation model (IDEM) are compared with (a) other global DEMs (30 m-resolution SRTM1 USGS v3 and 30 m-resolution Advanced Spaceborne Thermal Emission Reflectometer (ASTER GDEM2), (b) the local 25 m-resolution DEM made available by Tasmanian environmental authority (DPIPWE), and (c) over 15 000 accurate ground-control-points (GCPs) from the Australian National Gravity Database (ANGD). The comparison with ASTER and SRTM over the area of Tasmania involves over 500 million valid TanDEM-X IDEM elevations. The root-mean-square (RMS) of 8.8 m indicates a reasonable to good agreement of TanDEM-X IDEM and SRTM, while ASTER shows almost twice the disagreement in terms of RMS (∼16.5 m). Both, ASTER and SRTM show a (mean) offset of –1.9 m and –2.3 m w.r.t. TanDEM-X IDEM, respectively. By comparisons with GCPs, we find that SRTM and ASTER overestimate the terrain height. The comparison with the AGND GCPs also allows an estimate of the absolute accuracy of the IDEM, which is found to be superior to that of SRTM or ASTER. The RMS error of 6.6 m shows that the IDEM is close to the officially denoted 4 m absolute vertical accuracy considering that the GCPs are not error free. The height error map information layer is found to a suitable first indicator of the (local) accuracy of the IDEM in a relative sense. However, we find that the HEM tends to underestimate observed differences to the GCPs. Terrain-type analyses reveal that the TanDEM-X IDEM is a very consistent elevation database over Tasmania. In conclusion, our study demonstrates that the new TanDEM-X elevation data sets provide improved high-resolution terrain information over Tasmania and beyond.

Evaluation of TanDEM-X elevation data for geomorphological mapping and interpretation in high mountain environments — A case study from SE Tibet, China

Digital elevation models (DEMs) are a prerequisite for many different applications in the field of geomorphology. In this context, the two near-global medium resolution DEMs originating from the SRTM and ASTER missions are widely used. For detailed geomorphological studies, particularly in high mountain environments, these datasets are, however, known to have substantial disadvantages beyond their posting, i.e., data gaps and miscellaneous artifacts. The upcoming TanDEM-X DEM is a promising candidate to improve this situation by application of state-of-the-art radar technology, exhibiting a posting of 12m and less proneness to errors. In this study, we present a DEM processed from a single TanDEM-X CoSSC scene, covering a study area in the extreme relief of the eastern Nyainqêntanglha Range, southeastern Tibet. The potential of the resulting experimental TanDEM-X DEM for geomorphological applications was evaluated by geomorphometric analyses and an assessment of landform cognoscibility and artifacts in comparison to the ASTER GDEM and the recently released SRTM 1″ DEM. Detailed geomorphological mapping was conducted for four selected core study areas in a manual approach, based exclusively on the TanDEM-X DEM and its basic derivates. The results show that the self-processed TanDEM-X DEM yields a detailed and widely consistent landscape representation. It thus fosters geomorphological analysis by visual and quantitative means, allowing delineation of landforms down to footprints of ~30m. Even in this premature state, the TanDEM-X elevation data are widely superior to the ASTER and SRTM datasets, primarily owing to its significantly higher resolution and its lower susceptibility to artifacts that hamper landform interpretation. Conversely, challenges toward interferometric DEM generation were identified, including (i) triangulation facets and missing topographic information resulting from radar layover on steep slopes facing toward the radar sensor, (ii) low coherence values on leeward slopes, (iii) decorrelation effects over water bodies, and (iv) challenges for phase unwrapping in settings of strong topographic contrasts. There is, however, a high probability that these drawbacks can be overcome by applying multiple interferograms exhibiting different perpendicular baselines as planned for the generation of the final TanDEM-X DEM product.

APPLYING TERRAIN AND HYDROLOGICAL EDITING TO TANDEM-X DATA TO CREATE A CONSUMER-READY WORLDDEM PRODUCT

Abstract. The Geo-intelligence division of Airbus Defence and Space and the German Aerospace Center (DLR) have partnered to produce the first fully global, high-accuracy Digital Surface Model (DSM) using SAR data from the twin satellite constellation: TerraSAR-X and TanDEM-X. The DLR is responsible for the processing and distribution of the TanDEM-X elevation model for the world’s scientific community, while Airbus DS is responsible for the commercial production and distribution of the data, under the brand name WorldDEM™. For the provision of a consumer-ready product, Airbus DS undertakes several steps to reduce the effect of radar-specific artifacts in the WorldDEM data. These artifacts can be divided into two categories: terrain and hydrological. Airbus DS has developed proprietary software and processes to detect and correct these artifacts in the most efficient manner. Some processes are fullyautomatic, while others require manual or semi-automatic control by operators.

Fusion of Monostatic/Bistatic InSAR Stacks for Urban Area Analysis via Distributed Scatterers

Interferometric synthetic aperture radar (SAR) is a powerful technique providing meter-precision elevation maps and millimeter-precision surface displacement maps. Since 2007, the high-resolution SAR satellite TerraSAR-X allows monitoring of even single buildings from space using advanced monostatic repeat-pass stacking techniques. Furthermore, the launch of its twin satellite TanDEM-X in 2010 facilitates bistatic single-pass SAR interferometry. The main objective of this mission is the generation of a global digital elevation model. It also provides a configurable SAR platform for demonstrating new interferometric techniques and applications. However, in dense urban areas, standard TanDEM-X elevation models are inaccurate because ambiguities in radar layover areas cannot be solved. This letter describes the potential of joint monostatic and bistatic (motion-free and atmosphere-free) SAR interferometric stacking for an improved scene elevation and surface deformation estimation in complex urban areas. It involves exploiting distributed scatterers (DSs) using an advanced high-resolution small-baseline subset algorithm. Since most of the scatterers within a radar image can be classified as DSs, there is an increasing focus on an optimal processing of DSs for urban area monitoring. The fusion technique and an application test case are presented using a high-resolution spotlight mixed TerraSAR-X/TanDEM-X data stack of Las Vegas, USA.