TanDEM-X Digital Elevation Model Research Articles

Morphometric and structural parameters of impact craters in Algeria: Control of sedimentary target rocks and effect of post impact process

The Earth Impact Database (EID) currently includes four impact craters located in Algeria. These craters are well-exposed, morphologically visible, partially covered and all situated in a vast, very arid Saharan geological domain devoid of any vegetation cover. Consequently, they can be easily identified using the TanDEM-X digital elevation model and Alsat-1B satellite images. The aim of this work is to identify the characteristics of sedimentary target rocks that control the morphometric and structural parameters of Algerian craters, as well as the effects of post-impact processes. Crater exposure, type, and structure (depth-diameter ratio, rim-to-floor height, central peak and moat diameters), outline (circular, polygonal, elongated) and impactite types are therefore discussed. Relative or stratigraphic dating and erosion/burial rates are estimated for the craters. Results indicate that Amguid and Talemzane are simple, well-preserved young craters, closer to a pristine state. Tin Bider is a complex exposed structure showing an irregular outline with a well-developed central peak and two rings. Ouarkziz is a transitional crater; based on its diameter alone it is classified as a complex crater; however, a topographic central peak is not observed. A deep formation uplift is detected in the central zone, interpreted as a stratigraphic peak where the uplift has not reached significant heights to form a clearly visible peak. This may be due to the reduced diameter of Ouarkziz, which is smaller than what has always been described.

Accuracy assessment of global DEMs for the mapping of coastal flooding on a low-lying sandy environment: Cassino Beach, Brazil

Projected sea level rise in the 21st century, driven by climate change, threatens low-lying coastal areas with the risk of persistent flooding. Accurately estimating flooding extent and depth is crucial to implementing effective coastal management, with digital elevation models (DEMs) playing a pivotal role. Intrinsic inaccuracies of DEMs might lead to uncertainty in the flooding projections due to SLR scenarios, which are problematic for decision-makers. This work assessed the accuracy of five global digital elevation models for coastal flooding mapping on a low-lying sandy coastal environment in the south of Brazil (Cassino Beach). Five global DEMs were assessed, namely ALOS-AW3D30, ALOS-PALSAR, ASTER, SRTM, and TanDEM-X, and a high-resolution digital elevation model (created using local aerial vehicle (UAV) imagery) was used as a benchmark. A morphometric comparison was conducted between the five global DEMs and the high-resolution local DEMs. Several statistical metrics were calculated, including the root mean squared error, correlation coefficient, and bias.Additionally, flood depths and extent were computed for different scenarios of sea level rise, and comparisons between the different DEMs were quantified. Results show that among the DEMs evaluated, TanDEM-X DEM achieved the highest correlation with the UAV DEM elevation in the beach and dune region, presenting R² equal to 0.56 and RMSE equal to 0.88 m. On the other hand, the ALOS-AW3D30, ALOS-PALSAR, ASTER, and SRTM DEMs presented low correlation and RMSE values above 2.49 m. The analysis of coastal flooding extension and depths confirms that the TanDEM-X DEM exhibited the highest similarity with the UAV DEM across various sea level scenarios, and it was the only global DEM analyzed capable of capturing dune depressions and roads, which serve as primary pathways for flooding in the type of coastal region under consideration.

Improved monitoring of subglacial lake activity in Greenland

Abstract. Subglacial lakes form beneath ice sheets and ice caps if water is available and if bedrock and surface topography are able to retain the water. On a regional scale, the lakes modulate the timing and rate of freshwater flow through the subglacial system to the ocean by acting as reservoirs. More than 100 hydrologically active subglacial lakes that drain and recharge periodically have been documented under the Antarctic Ice Sheet, while only approximately 20 active lakes have been identified in Greenland. Active lakes may be identified by local changes in ice topography caused by the drainage or recharge of the lake beneath the ice. The small size of the Greenlandic subglacial lakes puts additional demands on mapping capabilities to resolve the evolving surface topography in sufficient detail to record their temporal behaviour. Here, we explore the potential for using CryoSat-2 swath-processed data, together with TanDEM-X digital elevation models, to improve the monitoring capabilities of active subglacial lakes in Greenland. We focus on four subglacial lakes previously described in the literature and combine the data with ArcticDEMs to obtain improved measurements of the evolution of these four lakes. We find that with careful tuning of the swath processor and filtering of the output data, the inclusion of these data, together with the TanDEM-X data, provides important information on lake activity, documenting, for example, that the ice surface collapse basin on Flade Isblink Ice Cap was 50 % (30 m) deeper than previously recorded. We also present evidence of a new, active subglacial lake in southwestern Greenland, which is located close to an already known lake. Both lakes probably drained within 1 month in the summer of 2012, which suggests either that they are hydrologically connected or that the drainages were independently triggered by extensive surface melt. If the hydrological connection is confirmed, this would to our knowledge be the first indication of hydrologically connected subglacial lakes in Greenland.

Evaluation of vertical accuracy of TanDEM-X Digital Elevation Model in Egypt

The study conducted aimed to examine the accuracy of Digital Elevation Models (DEMs) in Egypt, specifically the TanDEM-X mission's 30 m and 12 m resolution DEMs and the SRTM DEM with a 30 m resolution. The accuracy of DEMs is essential for various civil engineering and surveying applications, especially in geoscience applications. To ensure the comparison's accuracy, the study used ellipsoidal heights instead of orthometric heights, preventing errors caused by global geopotential models in the conversion process. The evaluation of the three DEMs was carried out using 352 GNSS points. The findings indicate that both TanDEM-X DEMs with 30 m and 12 m resolutions outperform the SRTM 30 m in terms of vertical accuracy, making them ideal for geomatic applications that require higher-resolution DEMs. The TanDEM-X 30 m generates a standard deviation (STD) and a Root Mean Square Error (RMSE) of approximately 3.03 m and 3.45 m, respectively. On the other hand, the TanDEM-X 12 m generates an STD and RMSE of approximately 2.86 m and 3.18 m, respectively. Comparatively, the SRTM 30 m produces an STD and RMSE of approximately 4.67 m and 5.35 m, respectively.

Vertical accuracy assessment for open-source digital elevation models using GPS control points and watershed basins delineation using GIS

Digital elevation models (DEMs) are crucial for numerous assessments of the Earth's surface, so this research aim to evaluate the quality of several open source DEMs like advanced spaceborne thermal emission and reflection radiometer global DEM (ASTER GDEM), shuttle radar topography mission DEM (SRTM DEM), SENTINEL-1, and TerraSAR-X for digital elevation measurement (TanDEM-X). TanDEM-X is one of the newest DEM models; however, ASTER and SRTM are still the most used. To evaluate the qualities of these DEMs, the vertical accuracies of ASTER, STRM (all 30 m), SRTM, TanDEM-X (90 m), and SENTINEL 1 (range from 5 to 12.5 m) were tested using GPS reference points and The RMSE gave the values of ± 3.56 m ± 57.68 m, ±5.89 m, ±10.21 m and ± 20.25 mfor used SRTM1, SENTINEL-1, SRTM3, TanDEM-X, and ASTER DEMs respectively. As is well known, obtaining a high-quality DEM is exceedingly challenging since it is time-consuming, expensive, and often constrained, therefore this study examined how to enhance SRTM1 as it gave the best result and assessed the effects of increasing the number of points on digital elevation model accuracy by using raster calculator and merge model in ArcGIS. The results showed that the merge model method gave the best result and, by increasing the number of reference points, the accuracy increased. The DEM produced by the enhanced SRTM (iSRTM) demonstrated noticeably better outcomes than the baseline SRTM DEM, with around 3.56 m RMSE.In this research, STRM-1 DEM is used to determine watershed basin delineation. The topographic map showed significant variations in the level of the Earth's surface, as the heights of the area ranged between 20 m and 120 m. The number of watersheds extracted in the Benban is 132 with different areas, the large area is about 72.14 km2, while the small area is about 1.13 km2, and between those areas, there are various areas. The largest recorded watershed circumference reached 48.94 km in area (72.14 km2), while the lowest recorded perimeter is 5.40 km for the area (1.13 km2).

Improving the Accuracy of TanDEM-X Digital Elevation Model Using Least Squares Collocation Method

The TanDEM-X Digital Elevation Model (DEM) is limited by the radar side-view imaging mode, which still has gaps and anomalies that directly affect the application potential of the data. Many methods have been used to improve the accuracy of TanDEM-X DEM, but these algorithms primarily focus on eliminating systematic errors trending over a large area in the DEM, rather than random errors. Therefore, this paper presents the least-squares collocation-based error correction algorithm (LSC-TXC) for TanDEM-X DEM, which effectively eliminates both systematic and random errors, to enhance the accuracy of TanDEM-X DEM. The experimental results demonstrate that TanDEM-X DEM corrected by the LSC-TXC algorithm reduces the root mean square error (RMSE) from 6.141 m to 3.851 m, resulting in a significant improvement in accuracy (by 37.3%). Compared to three conventional algorithms, namely Random Forest, Height Difference Fitting Neural Network and Back Propagation in Neural Network, the presented algorithm demonstrates a reduction in the RMSEs of the corrected TanDEM-X DEMs by 6.5%, 7.6%, and 18.1%, respectively. This algorithm provides an efficient tool for correcting DEMs such as TanDEM-X for a wide range of areas.

Spatial variability in melting on Himalayan debris-covered glaciers from 2000 to 2013

Glaciers covered by debris are widespread in the Himalayas. Debris layer makes the melting process of glaciers complicated, and the correlation between the spatial melt differences of glacier and its surface features is still not clear. The aim of this study was to identify possible causes of thickness changes for Himalayan debris-covered glaciers. Firstly, three high resolution Digital Elevation Model (DEM) datasets including SRTM DEM, AW3D and TanDEM-X DEM were used to estimate glacier thickness changes from 2000 to 2013. By checking and removing geometric displacements, systematic deviations and elevation-related bias, as well as correction of radar wave penetration depth in the clean glacier areas, reliable thickness change information in this complex glaciated region were provided. Then debris thicknesses on the glaciers were estimated. The surface lowering caused by ice cliffs or supraglacial ponds significantly reduces debris thickness. Finally, some surface features including debris thicknesses, spatial patterns of supraglacial ponds and ice cliffs extracted from high-resolution satellite images in different times, were comprehensively used to evaluate the main drivers of glacier melting differences. Results demonstrate that spatial variability of glacier melting in Himalayas is caused by the combined effects of debris thicknesses, ice cliffs and supraglacial lakes, with different dominant factors for different regions. The thickened glacier region, which mostly appears above 5300 m a.s.l., with minimal debris cover, displayed large patches of thickening and partial serious thinning in the debris-free areas. Although the thick debris layer (> 0.20 m) would slow down the glacier melting at the low-elevations, it leads to the heavy glacier thinning for the regions located 5000–5300 m a.s.l., where there are dense ice cliffs. In some areas with >1 m of average debris thickness, glaciers have thinned slowly because of erosion from the ice cliffs or large supraglacial ponds. Area and number of cliffs have proven to be key factors in controlling regional ablation for debris-covered glaciers, and supraglacial lakes serve as assistance.

Assessment of TanDEM-X DEM 2020 Data in Temperate and Boreal Forests and Their Application to Canopy Height Change

Space-borne digital elevation models (DEM) are considered as important proxy for canopy surface height and its changes in forests. Interferometric TanDEM-X DEMs were assessed regarding their accuracy in forests of Germany and Estonia. The interferometric synthetic aperture radar (InSAR) data for the new global TanDEM-X DEM 2020 coverage were acquired between 2017 and 2020. Each data acquisition was processed using the delta-phase approach for phase unwrapping and comprise an absolute height calibration. The results of the individual InSAR heights confirmed a substantial bias in forests. This was indicated by a mean error (ME) between – 5.74 and – 6.14 m associated with a root-mean-squared-error (RMSE) between 6.99 m and 7.40 m using airborne light detection and ranging (LiDAR) data as a reference. The bias was attributed to signal penetration, which was attempted to be compensated. The ME and RMSE improved substantially after the compensation to the range of – 0.54 to 0.84 m and 3.55 m to 4.52 m. Higher errors of the penetration depth compensated DEMs compared to the original DEMs were found in non-forested areas. This suggests to use the penetration compensation only in forests. The potential of the DEMs for estimating height changes was further assessed in a case study in Estonia. The canopy height change analysis in Estonia indicated an overall accuracy in terms of RMSE of 4.17 m and ME of – 0.93 m on pixel level comparing TanDEM-X and LiDAR height changes. The accuracy improved substantially at forest stand level to an RMSE of 2.84 m and an ME of – 1.48 m. Selective penetration compensation further improved the height change estimates to an RMSE of 2.14 m and an ME of – 0.83 m. Height loss induced by clearcutting was estimated with an ME of – 0.85 m and an RMSE of 3.3 m. Substantial regrowth resulted in an ME of – 0.46 m and an RMSE of 1.9 m. These results are relevant for exploiting multiple global acquisitions of TanDEM-X, in particular for estimating canopy height and its changes in European forests.

The Bureya Landslide Recent Evolution According to Spaceborne SAR Interferometry Data

The study presents the results of interferometric processing and analysis of ALOS-1/2 and Sentinel-1 SAR data acquired over the landslide territory of the Bureya river bank in 2006–2018. The novelty of the study is that, for the first time, the joint analysis of interferometric measurements of the landslide movement with meteorological information and time series of SRTM-X, ALOS-1, and TanDEM-X digital elevation models were performed. The results allowed us to make a conclusion that the Bureya landslide was evolving within the frame of the depression formed by a relict landslide which was stable at least at the beginning of the 21st century. The Bureya reservoir filling in 2003–2009 with a 60 m rise of the water and subsequent seasonal water level oscillations supposedly triggered the landslide activity. The landslide movement in the first decade may be characterized by a stable rate of movement all year around. A steady increase in precipitation level in the second decade, with heavy rainfalls in 2013, 2016, and 2018 led to a prominent acceleration of the landslide rate of movement, especially in warm seasons, with a final landslide in December 2018.

Quality Assessment of TanDEM-X DEM 12m Using GNSS-RTK and Airborne IFSAR DEM: A Case Study of Tuba Island, Langkawi

Digital elevation models (DEMs) have been recognized as a primary spatial dataset and essential for numerous scientific applications. The advent of TerraSAR-X for digital elevation measurement (TanDEM-X) has opened a new potential to obtain an accurate DEM. Nowadays, the demand/use of TanDEM-X DEM in scientific applications has become increasingly popular as it offers an alternative to the widely used DEMs: ASTER and SRTM DEM. Although many researches have been conducted to assess the performance of the TanDEM-X DEM at different locations in the world, however, only several multi-regional studies have been performed in Malaysian region. Currently, there are two types of DEMs published by DLR i.e., non-open access (12m and 30m resolution) and open access (90m resolution). In this article, the accuracy of TanDEM-X 12m has been comprehensively and systematically evaluated using 1284 GNSS-RTK control points over Tuba Island and airborne IFSAR-DEM as a reference height. Besides, four available global DEMs: TanDEM-X 90m, AW3D30 DEM, SRTM DEM, and ASTER DEM have also been evaluated to identify the accuracy of TanDEM-X DEM 12m. Based on the evaluation using GNSS-RTK points, TanDEM-X 12m exhibits the highest accuracy with an RMSE of ±1.553m. Unexpectedly, AW3D30 DEM shows a better performance compared to TanDEM-X 90m with RMSE of ±1.964m, followed by SRTM DEM with RMSE of ±3.296m Meanwhile, ASTER DEM exhibits the lowest accuracy with RMSE of ±4.100m The comparison of TanDEM-X 12m and the well-known DEM, SRTM DEM with airborne IFSAR-DEM shows the opposite results. Based on the topographic profile at flat and forest area, the SRTM-DEM exhibits better accuracy than TanDEM-X 12m

Semiautomatic inventory and geomorphological characterization of mass movements using high-resolution images and open-source software in the Ribeira de Iguape Valley, Brazil

In Brazil, as in many countries, inventories of mass movements usually exist for specific events and on a watershed scale and are predominantly produced from visual interpretation of aerial or orbital images, and those produced using automatic and semiautomatic methods are incipient in the national context. One of these events, the Ribeira de Iguape River Valley (Southeast Brazil), was severely affected by mass movements between January 13 and 14, 2014. The objective of this article was to produce a semiautomatic inventory and perform a brief geomorphological evaluation. of the mass movements triggered. A TanDEM-X digital elevation model (DEM) (12 m) was used to extract the watersheds (area: 109.7 km2) most affected by mass movements and multispectral images of the RapidEye satellites, captured before (01-10-2014) and after (01-30-2014) the event. From the multispectral images, the pre-event and post-event NDVI and the difference between the NDVI on these two dates were computed. Using the angle map, contribution area and topographic wetness index (TWI), the map of affected areas was refined into two classes: deposits of debris flows and other hydrodynamic mass movements (slope angle <6°; TWI <14; and contribution area >50,000 m2) and scars from shallow landslides (slope angle >6°; TWI <14; contribution area <50,000 m2). Approximately 5% of the total area was affected by mass movements, with 1.44 km2 of area corresponding to deposits of flows and other hydrodynamic mass movements and 4.04 km2 of area corresponding to scars from landslides. In total, 2089 landslide scars were mapped. The most affected slopes had angles between 20° and 40°, a TWI less than 9.0 and a concave curvature in profile and in planform, and approximately 90% of the scars occurred in areas covered by dense vegetation (NDVI >0.80 on 01-10-2014). The results may contribute to the expansion of the application of automatic and semiautomatic methods for the detection of mass movement scars in Brazil in a systematic manner using open source software.

Glacier inventory and recent variations of Santa Inés Icefield, Southern Patagonia

ABSTRACT The study of glaciers in remote regions improves our understanding of global glacier change. With an area of 149.31 ± 1.84 km2, the Santa Inés Icefield constitutes one of the largest and least studied and explored glaciated areas of Southern Patagonia. We study the extent and glacier variations of the Santa Inés Icefield over the last 75 years, and we generate the most detailed glacier inventory to date of its 24 constituting glaciers. We estimate surface elevation changes between 2000 and 2014 using Shuttle Radar Topography Mission (SRTM) and TanDEM-X digital elevation models. Our results show a generalized trend of retreat, with a glacier area loss of −9.78 ± 1.52 km2 between 1998 and 2020, with annual rate increase from −0.15 ± 0.01 km2 a−1 (1998–2005) to −0.58 ± 0.10 km2 a−1 (2005–2020), and an average thinning of 0.60 ± 0.26 m a−1 (2σ) between 2000 and 2014. No clear correlation was found between retreat or thinning rates and Accumulation Area Ratio (AAR), terminus slope, aspect, or glacier type. While ERA5 reanalysis data shows no significant climatic trends in temperature or precipitation, a small warming trend below our detection record is the most likely cause of the observed retreat and thinning of the Santa Inés Icefield.

Comparative analysis of the Copernicus, TanDEM-X, and UAV-SfM digital elevation models to estimate lavaka (gully) volumes and mobilization rates in the Lake Alaotra region (Madagascar)

Abstract. Over the past few decades, developments in remote sensing have resulted in an ever-growing availability of topographic information on a global scale. A recent development is TanDEM-X (TerraSAR-X add-on for digital elevation measurements), an interferometric synthetic aperture radar (SAR) mission of the Deutsche Zentrum für Luft- und Raumfahrt, providing near-global coverage and 12 m resolution digital elevation models (DEMs). Moreover, ongoing developments in uncrewed aerial vehicle (UAV) technology have enabled acquisitions of topographic information at a sub-meter resolution. Although UAV products are generally preferred for volume assessments of geomorphic features, their acquisition remains a time-consuming task and is spatially constrained. However, some applications in geomorphology, such as the estimation of regional or national erosion quantities of specific landforms, require data over large areas. TanDEM-X data can be applied at such scales, but this raises the question of how much accuracy is lost because of the lower spatial resolution. Here, we evaluated the performance of the 12 m TanDEM-X DEM to (i) estimate gully volume, (ii) establish an area–volume relationship, and (iii) determine mobilization rates through comparison with a higher-resolution (0.2 m) UAV structure-from-motion (SfM) DEM and a lower resolution (30 m) Copernicus DEM. We did this for six study areas in the Lake Alaotra region (central Madagascar), where lavaka (gullies) are omnipresent and surface area changes over the period 1949–2010s are available for 699 lavaka. Copernicus-derived lavaka volume estimates were systematically too low, indicating that the Copernicus DEM is too coarse to accurately estimate volumes of geomorphic features at the lavaka scale (100–105 m2). Lavaka volumes obtained from TanDEM-X were similar to UAV-SfM volumes for the largest features, whereas the volumes of smaller features were generally underestimated. To deal with this bias we introduce a breakpoint analysis to eliminate volume reconstructions that suffer from processing errors as evidenced by significant fractions of negative volumes. This elimination allowed the establishment of an area–volume relationship for the TanDEM-X data with fitted coefficients within the 95 % confidence interval of the UAV-SfM relationship. Our calibrated area–volume relationship enabled us to obtain large-scale lavaka mobilization rates ranging between 18 ± 3 and 311 ± 82 tha-1yr-1 for the six different study areas, with an average of 108 ± 26 tha-1yr-1 for the full dataset. These results indicate that current lavaka mobilization rates are 2 orders of magnitude higher than long-term erosion rates. With this study we demonstrate that the global TanDEM-X 12 m DEM can be used to accurately estimate volumes of gully-shaped features at the lavaka scale (100–105 m2), where the proposed breakpoint method can be applied without requiring the availability of a higher-resolution DEM. Furthermore, we use this information to make a first assessment of regional lavaka erosion rates in the central highlands of Madagascar.

Free Global DEMs and Flood Modelling—A Comparison Analysis for the January 2015 Flooding Event in Mocuba City (Mozambique)

Flood hazard and risk analysis in developing countries is a difficult task due to the absence or scarce availability of flow data and digital elevation models (DEMs) with the necessary quality. Up to eight DEMs (ALOS Palsar, Aster GDEM, Bare Earth DEM, SRTM DEM, Merit DEM, TanDEM-X DEM, NASA DEM, and Copernicus DEM) of different data acquisition, spatial resolution, and data processing were used to reconstruct the January 2015 flood event. The systematic flow rate record from the Mocuba city gauge station as well as international aid organisms and field data were used to define both the return period peak flows in years for different flood frequencies (Tyear) and the January 2015 flooding event peak flow. Both visual and statistical analysis of flow depth values at control point locations give us a measure of the different hydraulic modelling performance. The results related to the Copernicus DEM, both in visual and statistical approach, show a clear improvement over the results of the other free global DEMs. Under the assumption that Copernicus DEM provides the best results, a flood hazard analysis was carried out, its results being in agreement with previous data of the effects of the January 2015 flooding event in the Mocuba District. All these results highlight the step forward that Copernicus DEM represents for flood hazard analysis in developing countries, along with the use of so-called “citizen science” in the form of flooding evidence field data acquisition.

MirrorSAR: An HRWS Add-On for Single-Pass Multi-Baseline SAR Interferometry

This article reports the Phase A study results of the interferometric extension of the high-resolution wide-swath (HRWS) mission with three MirrorSAR satellites. According to the MirrorSAR concept, small, low-cost, transponder-like receive-only satellites without radar signal demodulation, digitization, memory storage, downlink, and synchronization are added to the planned German X-band HRWS mission. The MirrorSAR satellites fly a triple helix orbit in close formation around the HRWS orbit and span multiple single-pass interferometric baselines. A comprehensive system engineering and performance analysis is provided that includes orbit formation, MirrorLink, Doppler steering, antenna pattern and swath design, multi-static echo window timing, SAR performance, height performance, and coverage analysis. The overall interferometric system design analysis of Phase A is presented. The predicted performance of the global digital elevation model (DEM) is improved by one order of magnitude compared to presently available global DEM products such as the TanDEM-X DEM.

Generation of Dense and High-Precision Digital Elevation Model Using Low-Cost Unmanned Aerial Vehicle and Space-Borne TanDEM-X to Measure Exposed Area Change Due to Tidal Invasion

Tidal flats are internationally protected areas because of their environmental, geological, and economic value. Nevertheless, these are areas where casualties are common among visitors. To ensure the safety of visitors, efforts must be made to understand the geomorphologic characteristics of tidal flats. It is necessary to use three-dimensional topographic data to clearly determine when an exposed tidal flat rapidly disappears as a result of periodic tidal fluctuations. Digital elevation models (DEMs) created using unmanned aerial vehicle (UAV) imaging and commercial photogrammetric software to measure tidal flats are produced using ground control points (GCPs). It is difficult to conduct field surveys and readings of image coordinates that correspond to these because tidal flat areas are difficult to access. The distribution of GCPs affects the accuracy of a DEM because the entire test region cannot be covered during a survey. Without GCPs, the DEM generated with the UAV images and photogrammetric software using the structure from motion (SfM) technique probably has nonlinear distortion such as a bowl shape. This paper proposes a practical method of least-squares three-dimensional (3D) surface matching with a polynomial model (LS3D-PM) to correct a distorted DEM. For this LS3D-PM matching, a global TanDEM-X DEM was used instead of a field survey to collect the GCPs in a tidal flat. Practical testing was conducted using the proposed method. The root mean square error with respect to the height decreased from approximately 1.0 m to 0.1 m, and the bowl-effect error was eliminated. With the DEM corrected using the proposed method and the classified orthoimages, the exposed tidal flat changes due to seawater invasion were estimated at different times during flood tide. This method has non-trivial technical values for quick and relatively precise DEM generations at a low cost compared to that of other techniques, particularly in emergency situations such as tsunamis, landslides, and earthquakes.

Spatiotemporal Dynamics and Geodetic Mass Changes of Glaciers With Varying Debris Cover in the Pangong Region of Trans-Himalayan Ladakh, India Between 1990 and 2019

Glaciers across the Himalayan arc are showing varying signs of recession. Glaciers in the eastern and western parts of the Himalayan arc are retreating more rapidly as compared to other regions. This differential retreat is often attributed to climatic, topographic, and geologic influences. The glaciers in the Trans-Himalayan region of Ladakh are believed to be relatively stable as compared to other parts of the western Himalaya. The present study ascertained the area changes and frontal retreat of 87 glaciers in the Pangong Region between 1990 and 2019 using satellite data. The geodetic mass changes were also assessed using SRTM and TanDEM-X digital elevation models of 2000 and 2012 respectively. Besides, the glacier outlines were delineated manually and compared with existing regional and global glacier inventories that are available over the region. The GlabTop model was used to simulate the glacier-bed overdeepenings of four glaciers that are associated with a proglacial lake. The study also analyzed the impact of topographic influences and varying debris cover on glacier recession. This analysis indicated deglaciation of 6.7 ± 0.1% (0.23% a−1) from 1990 to 2019 over the Pangong Region with clean-ice glaciers showing a higher retreat (8.4 ± 0.28%) compared to the debris-covered glaciers (5.7 ± 0.14%). However, the overall recession is lower compared to other parts of northwestern Himalayas. The glacier recession showed a positive correlation with mean glacier slope (r = 0.3) and debris cover (r = 0.1) with bigger size glaciers having retreated at a lesser pace compared to smaller ones. This underpins the need for in-situ data about debris thickness to precisely ascertain the role of debris on glacier recession in the Trans-Himalayan Ladakh where debris thickness data is absent. The mean glacier elevation did not indicate any influence on glacier recession. From 2000 to 12, the glaciers lost an ice mass amounting to 0.33 ± 0.05 m we. per year. The formation of four new proglacial lakes, although small (&amp;lt;6 ha), need to be monitored using remote sensing data while the infrastructure development activities should not be permitted given glacial lake outburst flood risk.

Parameterized Modeling and Calibration for Orbital Error in TanDEM-X Bistatic SAR Interferometry over Complex Terrain Areas

The TerraSAR-X add-on for Digital Elevation Measurements (TanDEM-X) bistatic system provides high-resolution and high-quality interferometric data for global topographic measurement. Since the twin TanDEM-X satellites fly in a close helix formation, they can acquire approximately simultaneous synthetic aperture radar (SAR) images, so that temporal decorrelation and atmospheric delay can be ignored. Consequently, the orbital error becomes the most significant error limiting high-resolution SAR interferometry (InSAR) applications, such as the high-precision digital elevation model (DEM) reconstruction, subway and highway deformation monitoring, landslide monitoring and sub-canopy topography inversion. For rugged mountainous areas, in particular, it is difficult to estimate and correct the orbital phase error in TanDEM-X bistatic InSAR. Based on the rigorous InSAR geometric relationship, the orbital phase error can be attributed to the baseline errors (BEs) after fixing the positions of the master SAR sensor and the targets on the ground surface. For the constraint of the targets at a study scene, the freely released TanDEM-X DEM can be used, due to its consistency with the TanDEM-X bistatic InSAR-measured height. As a result, a parameterized model for the orbital phase error estimation is proposed in this paper. In high-resolution and high-precision TanDEM-X bistatic InSAR processing, due to the limited precision of the navigation systems and the uneven baseline changes caused by the helix formation, the BEs are time-varying in most cases. The parameterized model is thus built and estimated along each range line. To validate the proposed method, two mountainous test sites located in China (i.e., Fuping in Shanxi province and Hetang in Hunan province) were selected. The obtained results show that the orbital phase errors of the bistatic interferograms over the two test sites are well estimated. Compared with the widely applied polynomial model, the residual phase corrected by the proposed method contains little undesirable topography-dependent phase error, and avoids unexpected height errors ranging about from −6 m to 3 m for the Fuping test site and from −10 m to 8 m for the Hetang test site. Furthermore, some fine details, such as ridges and valleys, can be clearly identified after the correction. In addition, the two components of the orbital phase error, i.e., the residual flat-earth phase error and the topographic phase error caused by orbital error, are separated and quantified based on the parameterized expression. These demonstrate that the proposed method can be used to accurately estimate and mitigate the orbital phase error in TanDEM-X bistatic InSAR data, which increases the feasibility of reconstructing high-resolution and high-precision DEM. The rigorous geometric constraint, the refinement of the initial baseline parameters, and the assessment for height errors based on the estimated BEs are investigated in the discussion section of this paper.

The Global Water Body Layer from TanDEM-X Interferometric SAR Data

The interferometric synthetic aperture radar (InSAR) data set, acquired by the TanDEM-X (TerraSAR-X add-on for Digital Elevation Measurement) mission (TDM), represents a unique data source to derive geo-information products at a global scale. The complete Earth’s landmasses have been surveyed at least twice during the mission bistatic operation, which started at the end of 2010. Examples of the delivered global products are the TanDEM-X digital elevation model (DEM) (at a final independent posting of 12 m × 12 m) or the TanDEM-X global Forest/Non-Forest (FNF) map. The need for a reliable water product from TanDEM-X data was dictated by the limited accuracy and difficulty of use of the TDX Water Indication Mask (WAM), delivered as by-product of the global DEM, which jeopardizes its use for scientific applications, as well. Similarly as it has been done for the generation of the FNF map; in this work, we utilize the global data set of TanDEM-X quicklook images at 50 m × 50 m resolution, acquired between 2011 and 2016, to derive a new global water body layer (WBL), covering a range from −60∘ to +90∘ latitudes. The bistatic interferometric coherence is used as the primary input feature for performing water detection. We classify water surfaces in single TanDEM-X images, by considering the system’s geometric configuration and exploiting a watershed-based segmentation algorithm. Subsequently, single overlapping acquisitions are mosaicked together in a two-step logically weighting process to derive the global TDM WBL product, which comprises a binary averaged water/non-water layer as well as a permanent/temporary water indication layer. The accuracy of the new TDM WBL has been assessed over Europe, through a comparison with the Copernicus water and wetness layer, provided by the European Space Agency (ESA), at a 20 m × 20 m resolution. The F-score ranges from 83%, when considering all geocells (of 1∘ latitudes × 1∘ longitudes) over Europe, up to 93%, when considering only the geocells with a water content higher than 1%. At global scale, the quality of the product has been evaluated, by intercomparison, with other existing global water maps, resulting in an overall agreement that often exceeds 85% (F-score) when the content in the geocell is higher than 1%. The global TDM WBL presented in this study will be made available to the scientific community for free download and usage.

Effusion rate estimation based on solidified lava flows: Implications for volcanic hazard assessment in the Negros de Aras monogenetic volcanic field, northern Chile

Effusion rate is the instantaneous lava flow output by a vent. It is one of the most important factors that govern the emplacement and dynamics of lava flows and can be determined by direct measurements or estimated through modeling. The Negros de Aras monogenetic volcanic field, located in the Central Volcanic Zone of the Andes, is the largest volcanic field in northern Chile. It is situated north of the active Socompa volcano and south of the Salar de Atacama basin, consisting of scoria cones and lava flows. Here, we estimate the effusion rates of three overlapping and representative solidified lava flows from this volcanic field applying an iterative procedure using the Q-LavHA GIS plugin, where the effusion rate is treated as an unknown parameter and the solution is reached by comparing the simulated results with the real extension of the flows. The pre-eruptive surface was reconstructed using the 12 m resolution TanDEM-X digital elevation model. Other required input parameters for the modeling (e.g., channel ratio, viscosity, temperature) were estimated through geomorphometric, petrographic, and geochemical analysis. The estimated effusion rates vary between 14 and 113 m3/s, comparable with rates measured elsewhere. The method was validated by applying it to two directly measured (Nyamuragira 2006; Mount Etna 2001) and one calculated effusion rate (Lentiscal 2450 BP, Canary Islands). The estimated effusion rates gave an average underestimation of 10%. Considering this percentage of adjustment, the effusion rates for the three studied lava flows from the Negros de Aras monogenetic volcanic field vary from 15 m3/s to 124 m3/s. Our results provide valuable information for mitigating volcanic risk in the event of future lava flow eruptions, which could affect nearby villages and mining operations.