DEM Differencing Research Articles

Identification of Unstable Glacier Flow in the Western Tibetan Plateau and Karakoram Using Machine Learning

AbstractA novel method was developed for rapidly and accurately identifying unstable glacier flows, including pulse and surge events. The identification method was based on machine learning and high‐frequency glacier velocities derived from short time interval Sentinel‐1 Synthetic Aperture Radar (SAR) data. The method was built and tested using 32 glaciers in the eastern Pamir Plateau and applied it to 13 glaciers in western Karakoram. The test results showed that the success rate of identifying speedup events was more than 90% compared to manual interpretation results derived using velocity change maps and DEM differencing. The application results showed that there were some neglected pulse events, including two pulses on the Kukuar Glacier in 2017 and 2019, one pulse on the Karambar Glacier in 2017, and one pulse on the Ghulkin Glacier in 2016. Moreover, a complete surge event with multiple scattered pulses on the Shispare Glacier in 2018–2019 was also detected. The speedup events of the Shispare Glacier indicated the possibility of mutual transformation between pulse and surge events due to the influence of glacier basal roughness. In all unstable flows occurring within the test and application areas, pulse events could be observed on the nonsurging glaciers during the active phase and quiescent phase of the surge‐type glaciers, which might suggest the randomness of pulse events. Machine learning method made it possible to identify glacier speedup events in large areas with high efficiency and low manpower.

A new approach for 2-D and 3-D precise measurements of ground deformation from optimized registration and correlation of optical images and ICA-based filtering of image geometry artifacts

High resolution satellite images with improved spatial and temporal resolution provide unprecedented opportunities to monitor Earth Surface changes in 2D and 3D due, for example, to earthquakes, sand dune migration, ice flow, or landslides. The volume of imagery available for such measurements is rapidly growing but the exploitation of these data is challenging due to the various sources of geometric distortions of the satellite imagery. Here we propose a new approach to extract high-quality surface displacement in 3D based on the correlation of multi-date and multi-platform high resolution optical imagery. We additionally show that when a large enough volume of data is available, it is possible to separate the deformation signal from the artifacts due to the satellite jitter and misalignment of the CCDs, which, together with topographic artifacts, are the main source of noise in the measurements. Our method makes use of a reference DEM, but the outcome is independent of the characteristics of the chosen DEM. We use the case-example of the ground deformation caused by the Ridgecrest earthquake sequence to assess the performance of our proposed approach. We show that it outperforms the more standard approach which combines 2-D correlation and DEM differencing. With our technique, we were able to generate high quality measurements of coseismic ground displacement with GSD of 2.4 m, and uncertainties at the 90% confidence level on the NS, EW and vertical displacement measurements of 0.6 m, 0.7 m, and 0.6 m respectively.

An Accurate Digital Subsidence Model for Deformation Detection of Coal Mining Areas Using a UAV-Based LiDAR

Coal mine surface subsidence detection determines the damage degree of coal mining, which is of great importance for the mitigation of hazards and property loss. Therefore, it is very important to detect deformation during coal mining. Currently, there are many methods used to detect deformations in coal mining areas. However, with most of them, the accuracy is difficult to guarantee in mountainous areas, especially for shallow seam mining, which has the characteristics of active, rapid, and high-intensity surface subsidence. In response to these problems, we made a digital subsidence model (DSuM) for deformation detection in coal mining areas based on airborne light detection and ranging (LiDAR). First, the entire point cloud of the study area was obtained by coarse to fine registration. Second, noise points were removed by multi-scale morphological filtering, and the progressive triangulation filtering classification (PTFC) algorithm was used to obtain the ground point cloud. Third, the DEM was generated from the clean ground point cloud, and an accurate DSuM was obtained through multiple periods of DEM difference calculations. Then, data mining was conducted based on the DSuM to obtain parameters such as the maximum surface subsidence value, a subsidence contour map, the subsidence area, and the subsidence boundary angle. Finally, the accuracy of the DSuM was analyzed through a comparison with ground checkpoints (GCPs). The results show that the proposed method can achieve centimeter-level accuracy, which makes the data a good reference for mining safety considerations and subsequent restoration of the ecological environment.

Rapid glacier mass loss in the Southeastern Tibetan Plateau since the year 2000 from satellite observations

Maritime glaciers in the Southeastern Tibetan Plateau (SETP) featuring the largest maritime glaciers in the Tibetan Plateau (TP) have been experiencing dramatic mass loss and interannual variability over the past two decades, increasing risks of glacier avalanches and glacial lake outbursts. However, spatially explicit and high-temporal-resolution glacier mass loss over the entire SETP has not been well quantified. We developed an approach to integrate satellite altimetry (ICESat, CryoSat-2, and ICESat-2) with DEM differencing and satellite gravity to resolve high spatiotemporally resolved glacier surface elevation change and mass balance across the SETP for the past two decades. We generated DEMs from ASTER L1A stereo-images to estimate the multi-year elevation change, which was used to correct for the altimetry-based counterpart. Subsequently, we processed three different satellite altimetry data and total water storage (TWS) products specifically. Finally, we obtained time series of glacier elevation change and mass balance through the integration of satellite altimetry-, satellite gravity-, and DEM-derived elevation changes during 2000–2020. Results show rapid and heterogeneous glacier depletion with a mean mass loss rate of −0.66 ± 0.02 m water equivalent (w.e.)/yr during 2003–2020 and an accelerating trend over the past two decades. The strongest downwasting was observed in the Hengduan Mountains (−1.29 ± 0.32 m w.e./yr). Contiguous glaciers distributed mostly in Bomi County have a slower rate of elevation changes but play a dominant role in the regional mass balance. Glacier terminus types have a significant impact on glacier melting. The mass loss rate of lake-terminating glaciers is 45% higher than that of land-terminating glaciers, suggesting increasing risks of glacial lake outbursts caused by rapid glacier melting across the SETP. These spatially explicit and high-temporal-resolution features of glacier mass loss will be extremely valuable for calibrating and validating glaciological and hydrological models. Our approach also shows a promising application of CryoSat-2 to mountain glaciology and its potential of estimating glacier mass balances over similar regions globally.

Reconstructing the Chongbaxia Tsho glacial lake outburst flood in the Eastern Himalaya: Evolution, process and impacts

Glacial lake outburst floods (GLOF) are one of the most destructive natural disasters. Understanding GLOF evolution, and their impacts, plays a fundamental role in GLOF hazard assessment and risk management. Reconstructing historical GLOFs is an important exercise because detailed case studies of such glacial hazards are rare, which hinders the capacity of glacial hazard practitioners to learn from these events. In this study, we reconstruct a historical GLOF from moraine-dammed Chongbaxia Tsho (89.745°E, 28.211°N) in the Eastern Himalaya, which is a unique case study because the outburst flood cascaded into two further lakes downstream. We employ a combination of i) multi-source and multi-temporal satellite imagery, ii) field investigation (including an unmanned aerial vehicle survey), iii) numerical dam breach and hydrodynamic modelling and, iv) qualitative and quantitative cryospheric and meteorological analysis, to investigate the evolution of the GLOF hazard, simulate moraine dam failure and GLOF propagation, and explore the role that long- and short-term climate trends played in providing the conditioning factors for the outburst. Chongbaxia Tsho expanded rapidly between 1987 until 2001 in response to glacier recession most likely caused by a regional warming trend of +0.37 °C per decade. Based on satellite image analysis we refine the outburst date to be 6 August 2001, instead of 6 August 2000, as previously reported, and attribute an ice avalanche into the glacial lake originating from the receding parent glacier as the most likely trigger for moraine dam failure. Through DEM differencing and lake level decrease, we estimate that a total water volume of 27.1 ± 1.6 × 106 m3 was released from the lake during the event, and using dam breach modelling we estimate that the peak discharge at the breach was >6600 m3 s−1. The GLOF flowed through downstream Chongbamang Tsho and Chongbayong Tsho, both of which served to attenuate the GLOF and reduce downstream losses; the latter stored an estimated 96% of the flood volume. Precipitation totals in the weeks preceding the GLOF exceeded the historical mean by up to 40%, and may have contributed to instability of the parent glacier, and generation of an ice avalanche with enough impact energy to cause lake water to overtop the moraine dam and initiate breach development. A future GLOF from Chongbaxia Tsho cannot be ruled out, but more field data, including detailed lake bathymetry, and information pertaining to the sedimentological and geotechnical characteristics of the moraine dam, are required for a more robust parameterization of a predictive GLOF model and quantification of the hazard posed by a future GLOF.

Geomorphological mapping and anthropogenic landform change in an urbanizing watershed using structure-from-motion photogrammetry and geospatial modeling techniques

ABSTRACT Increasing urbanization and suburban growth in cities globally has highlighted the importance of land planning using detailed geomorphologic maps that depict anthropogenic landform changes. Such mapping provides information crucial for land management, hazard identification, and the management of the challenges arising from urbanization. The development and use of quantitative and repeatable methods to map anthropogenic and natural processes are required to advance the science of urban geomorphological mapping. This study investigated the application of geospatial modeling, structure-from-motion (SfM) photogrammetric methods and DEM differencing as means of quantifying anthropogenic landform changes from archival aerial imagery. Anthropogenic landforms were incorporated into a detailed geomorphologic map in an urbanizing watershed located in the Washington, D.C. metropolitan suburb of Vienna, Virginia.

The hazardous 2017\u20132019 surge and river damming by Shispare Glacier, Karakoram

In 2017–2019 a surge of Shispare Glacier, a former tributary of the once larger Hasanabad Glacier (Hunza region), dammed the proglacial river of Muchuhar Glacier, which formed an ice-dammed lake and generated a small Glacial Lake Outburst Flood (GLOF). Surge movement produced the highest recorded Karakoram glacier surface flow rate using feature tracking (~18 ± 0.5 m d−1) and resulted in a glacier frontal advance of 1495 ± 47 m. The surge speed was less than reports of earlier Hasanabad advances during 1892/93 (9.3 km) and 1903 (9.7 km). Surges also occurred in 1973 and 2000–2001. Recent surges and lake evolution are examined using feature tracking in satellite images (1990–2019), DEM differencing (1973–2019), and thermal satellite data (2000–2019). The recent active phase of Shispare surge began in April 2018, showed two surface flow maxima in June 2018 and May 2019, and terminated following a GLOF on 22–23 June 2019. The surge likely had hydrological controls influenced in winter by compromised subglacial flow and low meltwater production. It terminated during summer probably because increased meltwater restored efficient channelized flow. We also identify considerable heterogeneity of movement, including spring/summer accelerations.

Research on Forest Height Inversion Algorithm of Three-Stage Full-Polarization SAR Data Based on Improved Coherence Coefficient

Polarimetric SAR interference technology (PolInSAR) has a wide range of applications in the extraction of forest height. At present, some commonly used tree height inversion algorithms, such as ESPRIT algorithm and DEM difference method, seriously underestimate the forest tree height. In this paper, in the process of traditional three-stage algorithm, the extraction of the coherence coefficient is improved, and the improved coherence coefficient is more accurate, thus greatly improving the accuracy of three-stage algorithm tree height inversion results. By highly inverting the 25 m data generated by the PolSARPro simulation software, it is found that the height before the improvement of the coherence coefficient is 18.2 m, and the improved height is 23.7 m.

Short communication: Challenges and applications of structure-from-motion photogrammetry in a physical model of a braided river

Abstract. For extending the applications of structure-from-motion (SfM) photogrammetry in river flumes, we present the main challenges and methods used to collect a large dataset (>1000 digital elevation models, DEMs) of high-quality topographic data using close-range SfM photogrammetry with a resulting vertical precision of ∼1 mm. Automatic target detection, batch processing, and considerations for image quality were fundamental to the successful implementation of the SfM technique on such a large dataset, which was used primarily for capturing details of gravel-bed braided river morphodynamics and sedimentology. While the applications of close-range SfM photogrammetry are numerous, we include sample results from DEM differencing, which was used to quantify morphology change and provide estimates of water depth in braided rivers, as well as image analysis for mapping bed surface texture. These methods and results contribute to the growing field of SfM applications in geomorphology and close-range experimental settings in general.

Contribution of UAS to the monitoring at the Lärchberg-Galgenwald landslide (Austria)

ABSTRACTIn April 2001, a rock fall occurred at the landslide Lärchberg-Galgenwald, Austria. The movement of this landslide has been under observation for decades, but the methods used so far have several disadvantages. This article aims to show that unmanned aerial systems (UAS) provide a reasonable alternative in terms for monitoring the landslide. At the landslide, we focused on the most active area to (i) record changes of the landslide’s surface, (ii) assess the accuracy of the resulting data, (iii) assess whether the number of ground control points (GCPs) could be reduced in subsequent UAS surveys, and (iv) conclude whether UAS-based recording is favourable compared to common terrestrial methods. UAS imagery, acquired under challenging site conditions in November 2015 and May 2016, were processed to digital elevation models and orthophotos with a ground sampling distance of 0.04 m, which should display expected changes of up to ~0.17 m (relating to previously reported movements of up to 30 cm a−1) for the same period of time. Using DEM differencing, we calculated a vertical difference that was in the range of a few centimetres in most cases with only a few localized areas of much larger change. The latter are mainly related to single objects moving such as rock blocks or tree trunks. Apart from that, no general surface elevation lowering (a threshold of 0.27 m was used to distinguish significant from insignificant changes) could be detected. Based on the resulting orthophotos, we calculated vectors of horizontal displacement, which confirmed that the changes are related to single objects and revealed that in upcoming flight campaigns the number of GCPs can be generously reduced with an acceptable loss of positional accuracy. Therefore, the suitability of UAS for expanding the monitoring approaches used at Lärchberg-Galgenwald landslide is described.

Error sources and guidelines for quality assessment of glacier area, elevation change, and velocity products derived from satellite data in the Glaciers_cci project

Satellite data provide a large range of information on glacier dynamics and changes. Results are often reported, provided and used without consideration of measurement accuracy (difference to a true value) and precision (variability of independent assessments). Whereas accuracy might be difficult to determine due to the limited availability of appropriate reference data and the complimentary nature of satellite measurements, precision can be obtained from a large range of measures with a variable effort for determination. This study provides a systematic overview on the factors influencing accuracy and precision of glacier area, elevation change (from altimetry and DEM differencing), and velocity products derived from satellite data, along with measures for calculating them. A tiered list of recommendations is provided (sorted for effort from Level 0 to 3) as a guide for analysts to apply what is possible given the datasets used and available to them. The more simple measures to describe product quality (Levels 0 and 1) can often easily be applied and should thus always be reported. Medium efforts (Level 2) require additional work but provide a more realistic assessment of product precision. Real accuracy assessment (Level 3) requires independent and coincidently acquired reference data with high accuracy. However, these are rarely available and their transformation into an unbiased source of information is challenging. This overview is based on the experiences and lessons learned in the ESA project Glaciers_cci rather than a review of the literature.

Surge dynamics in the Nathorstbreen glacier system, Svalbard

Abstract. Nathorstbreen glacier system (NGS) recently experienced the largest surge in Svalbard since 1936, and this was examined using spatial and temporal observations from DEM differencing, time series of surface velocities from satellite synthetic aperture radar (SAR) and other sources. The upper basins with maximum accumulation during quiescence corresponded to regions of initial lowering. Initial speed-up exceeded quiescent velocities by a factor of several tens. This suggests that polythermal glacier surges are initiated in the temperate area before mass is displaced downglacier. Subsequent downglacier mass displacement coincided with areas where glacier velocity increased by a factor of 100–200 times (stage 2). After more than 5 years, the joint NGS terminus advanced abruptly into the fjord during winter, increasing velocities even more. The advance was followed by up-glacier propagation of crevasses, indicating the middle and subsequently the upper part of the glaciers reacting to the mass displacement. NGS advanced ~15 km, while another ~3 km length was lost due to calving. Surface lowering of ~50 m was observed in some up-glacier areas, and in 5 years the total glacier area increased by 20%. Maximum measured flow rates were at least 25 m d−1, 2500 times quiescent velocity, while average velocities were about 10 m d−1. The surges of Zawadzkibreen cycle with ca. 70-year periods.

Establishes the Precise Three-Dimensional Terrain Method Study Based on Anudem

Take a typical region in the Loess Plateau of North Shaanxi Province zone as the study area.Based on relief map with a scale of 1:1000 to generate accurate 3D terrain DEM using Anudem algorithm. Compared with the production of Anudem method TIN method and Kriging method between DEM. DEM accuracy evaluation including value target, profile and slope and terrain attribute visualization, contour line playbacking and different differential value algorithm result variance analysis. The DEM difference that the result demonstrates that the different algorithm obtains is big, and DEM precision of Anudem method production is best, can very good response precise three-dimensional terrain.

Comparative Analysis of Forest Height Retrieval Methods by Polarimetric SAR Interferometry

The objective of this paper is to compare and analyze the forest height retrieval methods from Polarimetric SAR Interferometry(POLINSAR).Both of the methods based on DEM difference and that on interferometry coherence amplitude are generalized, analyzed, and compared.Also in this paper combined methods of DEM difference and interferometry coherence amplitude are proposed and validated.The ESA fullpolarimetric interferometry L-band data are used for forest height analysis.The results show that the height is severely underestimated using DEM difference method,In constast,interferometry coherence amplitude method has a overest imation of height.The combined method of DEM difference and interferometry coherence amplitude has a much better estimate,closer to the true height than these two methods.

Impact of resolution and radar penetration on glacier elevation changes computed from DEM differencing

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Geomorphic change detection using historic maps and DEM differencing: The temporal dimension of geospatial analysis

The ability to develop spatially distributed models of topographic change is presenting new capabilities in geomorphic research. High resolution maps of elevation change indicate locations, processes, and rates of geomorphic change, and provide a means of calibrating temporal simulation models. Methods of geomorphic change detection (GCD), based on gridded models, may be applied to a wide range of time periods by utilizing cartometric, remote sensing, or ground-based topographic survey data to measure volumetric change. Advantages and limitations of historical DEM reconstruction methods are reviewed with a focus on coupling them with subsequent DEMs to construct DEMs of difference (DoD), which can be created by subtracting one elevation model from another, to map erosion, deposition, and volumetric change. The period of DoD analysis can be extended to several decades if accurate historical DEMs can be generated by extracting topographic data from historical data and selecting areas where geomorphic change has been substantial. The challenge is to recognize and minimize uncertainties in data that are particularly elusive with early topographic data. This paper reviews potential sources of error in digitized topographic maps and DEMs. Although the paper is primarily a review of methods, three brief examples are presented at the end to demonstrate GCD using DoDs constructed from data extending over periods ranging from 70 to 90 years.

Spatial variability of glacier elevation changes in the Swiss Alps obtained from two digital elevation models

Massive glacier thinning in the Alps during the past 20 years is documented by direct mass balance measurements on nine regularly observed glaciers. How representative this limited sample of glaciers is for the entire Alps, however, remained uncertain. The near‐global digital terrain model from the SRTM enables a closer analysis of this question, which is of fundamental importance to assess overall glacier volume change. Here we present elevation changes from 1985 to 1999 for about 1050 glaciers in the Swiss Alps. The analysis reveals extreme thickness losses (>80 m) for flat/low‐lying glacier tongues and a strong overall surface lowering. The mean cumulative mass balance of the nine glaciers with direct measurements (−10.8 m w.e.) agrees well with the mean change of the entire region from DEM differencing (−11 m w.e.) and can thus be considered to be representative. Mean thickness change of individual glaciers is correlated with their size, elevation, and exposure to solar irradiation. This implies that mass losses of large glaciers can be underestimated when they are directly inferred from values measured at much smaller glaciers.

An attempt to calculate DEM difference using Minimum RMSE method

An attempt to calculate DEM difference using Minimum RMSE method