| 1. |
- Darvishi, Mehdi, et al.
(författare)
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Performance evaluation of phase and weather-based models in atmospheric correction with Sentinel-1data: Corvara landslide in the Alps
- 2020
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Ingår i: IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing. - : IEEE. - 1939-1404 .- 2151-1535. ; 13, s. 1332-1346
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Tidskriftsartikel (refereegranskat)abstract
- Phase delay caused by atmospheric effects due to spatial and temporal variations of pressure, temperature, and water vapor content is one of the major errors ources in estimation of ground deformation by interferometric synthetic aperture radar (InSAR). Therefore, accuracy of ground deformation measurement is highly contingent on the robustness of the atmospheric correction techniques. These techniques rely eitheron auxiliary data such as numerical weather models or on the analysis of the interferometric phase itself. The accuracyin phase delays estimation of mixing effectsof turbulent delay in atmosphere and stratified delay in lower troposphere is a key factor in determination of performanceof each technique. Hence, the performance evaluation of the techniques is required in order toassess their potentials, robustness and limitations. This paper analyzes and evaluates the performance of four numerical weather models (i.e., ERA-Interim, ERA5, MERRA2 and WRF) and two phase-based techniques (i.e., linear and power law) to estimate phase delay using Sentinel-1A/B data over the Corvara landslide located in the Alps. The GPS data and GACOS product were used to validate the results. We generally found that ERA5 outperformed among other weather models with a phase standard deviation reduction of 77.7%(with respect to the InSAR phase), a correlation coefficient of 0.86 (between InSAR phase and estimated tropospheric delay) and a less significant error in the velocity estimation of the landslide.
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| 2. |
- Edey, A., et al.
(författare)
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Kinematic variation within the Fars Arc, eastern Zagros, and the development of fold‐and‐thrust belt curvature
- 2020
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Ingår i: Tectonics. - : AGU. - 0278-7407 .- 1944-9194. ; 39:8
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Tidskriftsartikel (refereegranskat)abstract
- We analyze deformation of the Fars Arc in the eastern Zagros, Iran, including earthquake slip vectors, GPS velocities, paleomagnetism data, and fold orientations, to understand how this fold‐and‐thrust belt works, and so better understand the generic issue of fold‐and‐thrust belt curvature. The Fars Arc is curved, convex southwards. GPS‐derived rotation rates are ≤0.5° Myr‐1: rotation is clockwise west of 53° E, and counter‐clockwise to the east. These rotation senses are opposite to previous predictions of passive “bookshelf” models for strike‐slip faults during north‐south convergence. West of 53° E, average GPS vectors, thrust earthquake slip vectors, strain axes derived from GPS data and orthogonal directions to fold trends are all aligned, towards ~218°. East of this meridian, the average GPS vector is towards 208°, but the averages of the other datasets are distinctly different, all towards ~190°. We propose that fault blocks in eastern Fars, each ~20‐40 km long, rotate predominantly counter‐clockwise, whereas in western Fars the regional clockwise rotation takes place mainly on the array of active right‐lateral faults in this area. Thus localized block faulting and rotations accumulate to produce the overall strain and regional curvature. Active folds of different orientations in eastern Fars intersect to produce domal interference patterns, without involving separate deformation phases, indicating that fold interference patterns should not be interpreted in terms of changing stress orientations unless there is clear evidence. Fars Arc curvature is best explained by deformation being restricted at tectonic boundaries at its eastern and western margins, without significant gravitational spreading.
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| 3. |
- Gido, Nureldin A. A., et al.
(författare)
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Localized Subsidence Zones in Gavle City Detected by Sentinel-1 PSI and Leveling Data
- 2020
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Ingår i: Remote Sensing. - : MDPI. - 2072-4292. ; 12:16
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Tidskriftsartikel (refereegranskat)abstract
- Among different sets of constraints and hazards that have to be considered in the management of cities and land use, land surface subsidence is one of the important issues that can lead to many problems, and its economic consequences cannot be ignored. In this study, the ground surface deformation of Gavle city in Sweden is investigated using the Persistent Scatterer Interferometry (PSI) technique as well as analyzing the historical leveling data. The PSI technique is used to map the location of hazard zones and their ongoing subsidence rate. Two ascending and descending Sentinel-1 datasets, collected between January 2015 and May 2020, covering the Gavle city, were processed and analyzed. In addition, a long record of a leveling dataset, covering the period from 1974 to 2019, was used to detect the rate of subsidence in some locations which were not reported before. Our PSI analysis reveals that the center of Gavle is relatively stable with minor deformation ranged between -2 +/- 0.5 mm/yr to +2 +/- 0.5 mm/yr in vertical and east-west components. However, the land surface toward the northeast of the city is relatively subsiding with a higher annual rate of up to -6 +/- 0.46 mm/yr. The comparison at sparse locations shows a close agreement between the subsidence rates obtained from precise leveling and PSI results. The regional quaternary deposits map was overlaid with PSI results and it shows the subsidence areas are mostly located in zones where the subsurface layer is marked by artificial fill materials. The knowledge of the spatio-temporal extents of land surface subsidence for undergoing urban areas can help to develop and establish models to mitigate hazards associated with such land settlement.
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| 4. |
- Gido, Nureldin A. A., et al.
(författare)
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Satellite monitoring of mass changes and ground subsidence in Sudan’s oil fields using GRACE and Sentinel-1 data
- 2020
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Konferensbidrag (populärvet., debatt m.m.)abstract
- Monitoring environmental hazards, due to natural and anthropogenic causes, is one of the important issues, which requires proper data, models, and cross-validation of the results. The geodetic satellite missions, e.g. the Gravity Recovery and Climate Experiment (GRACE) and Sentinel-1, are very useful in this aspect. GRACE missions are dedicated to model the temporal variations of the Earth’s gravity field and mass transportation in the Earth’s surface, whereas Sentinel-1 collects Synthetic Aperture Radar (SAR) data which enables us to measure the ground movements accurately. Extraction of large volumes of water and oil decreases the reservoir pressure, form compaction and consequently land subsidence occurs which can be analyzed by both GRACE and Sentinel-1 data. In this paper, large-scale groundwater storage (GWS) changes are studied using the GRACE monthly gravity field models together with different hydrological models over the major oil reservoirs in Sudan, i.e. Heglig, Bamboo, Neem, Diffra and Unity-area oil fields. Then we correlate the results with the available oil wells production data for the period of 2003-2012. In addition, using the only freely available Sentinel-1 data, collected between November 2015 and April 2019, the ground surface deformation associated with this oil and water depletion is studied. Due to the lack of terrestrial geodetic monitoring data in Sudan, the use of GRACE and Sentinel-1 satellite data is very valuable to monitor water and oil storage changes and their associated land subsidence over our region of interest. Our results show that there is a significant correlation between the GRACE-based GWS change and extracted oil and water volumes. The trend of GWS changes due to water and oil depletion ranged from -18.5 to -6.2mm/year using the CSR GRACE monthly solutions and the best tested hydrological model in this study. Moreover, our Sentinel-1 SAR data analysis using Persistent Scatterer Interferometry (PSI) method shows high rate of subsidence i.e. -24.5, -23.8, -14.2 and -6 mm/year over Heglig, Neem, Diffra and Unity-area oil fields respectively. The results of this study can help us to control the integrity and safety of operations and infrastructure in that region, as well as to study the groundwater/oil storage behavior.
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| 5. |
- Gido, Nureldin A. A., et al.
(författare)
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Satellite Monitoring of Mass Changes and Ground Subsidence in Sudan's Oil Fields Using GRACE and Sentinel-1 Data
- 2020
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Ingår i: Remote Sensing. - : MDPI AG. - 2072-4292. ; 12:11
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Tidskriftsartikel (refereegranskat)abstract
- Monitoring environmental hazards, owing to natural and anthropogenic causes, is an important issue, which requires proper data, models, and cross-validation of the results. The geodetic satellite missions, for example, the Gravity Recovery and Climate Experiment (GRACE) and Sentinel-1, are very useful in this respect. GRACE missions are dedicated to modeling the temporal variations of the Earth's gravity field and mass transportation in the Earth's surface, whereas Sentinel-1 collects synthetic aperture radar (SAR) data, which enables us to measure the ground movements accurately. Extraction of large volumes of water and oil decreases the reservoir pressure and form compaction and, consequently, land subsidence occurs, which can be analyzed by both GRACE and Sentinel-1 data. In this paper, large-scale groundwater storage (GWS) changes are studied using the GRACE monthly gravity field models together with different hydrological models over the major oil reservoirs in Sudan, that is, Heglig, Bamboo, Neem, Diffra, and Unity-area oil fields. Then, we correlate the results with the available oil wells production data for the period of 2003-2012. In addition, using the only freely available Sentinel-1 data, collected between November 2015 and April 2019, the ground surface deformation associated with this oil and water depletion is studied. Owing to the lack of terrestrial geodetic monitoring data in Sudan, the use of GRACE and Sentinel-1 satellite data is very valuable to monitor water and oil storage changes and their associated land subsidence over our region of interest. Our results show that there is a significant correlation between the GRACE-based GWS anomalies (Delta GWS) and extracted oil and water volumes. The trend of Delta GWS changes due to water and oil depletion ranged from -18.5 +/- 6.3 to -6.2 +/- 1.3 mm/year using the CSR GRACE monthly solutions and the best tested hydrological model in this study. Moreover, our Sentinel-1 SAR data analysis using the persistent scatterer interferometry (PSI) method shows a high rate of subsidence, that is, -24.5 +/- 0.85, -23.8 +/- 0.96, -14.2 +/- 0.85, and -6 +/- 0.88 mm/year over Heglig, Neem, Diffra, and Unity-area oil fields, respectively. The results of this study can help us to control the integrity and safety of operations and infrastructure in that region, as well as to study the groundwater/oil storage behavior.
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| 6. |
- Gruber, Thomas, et al.
(författare)
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Geodetic SAR for Height System Unification and Sea Level Research - Observation Concept and Preliminary Results in the Baltic Sea
- 2020
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Ingår i: Remote Sensing. - : MDPI AG. - 2072-4292. ; 12:22
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Tidskriftsartikel (refereegranskat)abstract
- Traditionally, sea level is observed at tide gauge stations, which usually also serve as height reference stations for national leveling networks and therefore define a height system of a country. One of the main deficiencies to use tide gauge data for geodetic sea level research and height systems unification is that only a few stations are connected to the geometric network of a country by operating permanent GNSS receivers next to the tide gauge. As a new observation technique, absolute positioning by SAR using active transponders on ground can fill this gap by systematically observing time series of geometric heights at tide gauge stations. By additionally knowing the tide gauge geoid heights in a global height reference frame, one can finally obtain absolute sea level heights at each tide gauge. With this information the impact of climate change on the sea level can be quantified in an absolute manner and height systems can be connected across the oceans. First results from applying this technique at selected tide gauges at the Baltic coasts are promising but also exhibit some problems related to the new technique. The paper presents the concept of using the new observation type in an integrated sea level observing system and provides some early results for SAR positioning in the Baltic sea area.
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| 7. |
- Jouybari, Arash, et al.
(författare)
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Assessment of Different GNSS and IMU Observation Weights on Photogrammetry Aerial Triangulation
- 2020
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Konferensbidrag (refereegranskat)abstract
- Nowadays, the Global Navigation Satellite System (GNSS) and Inertial Navigation System (INS) are playing a prominent character in high accuracy navigation applications. Beside camera calibration and tie points which are crucial, GNSS shift and drift errors, which caused by either unknown GNSS antenna-eccentricity, atmospheric effect, GNSS and INS observation qualities, unsolved datum correction between coordinate systems and far away GNSS reference stations from the project area, are important factors in bundle block adjustment ultimate accuracy. In this study, the influence of different a priori observation uncertainties of GNSS and Inertial Measurement Unit (IMU) using block- Aerial Triangulation (AT) method is examined. We investigate the effect of IMU and GNSS uncertainties on the final AT results using Trimble Inpho Match-AT software by evaluating the checkpoints RMS residual and employing a statistical t-test for determining the number of images with the gross error. In our study area, the most trustworthy observation uncertainties was 0.2, 0.2, 0.2 meter for East, North, and Height of the GNSS components respectively, and 0.007, 0.007, 0.009 for Omega, Phi, and Kappa for the IMU orientations, respectively.
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| 8. |
- Kaviani, Ayoub, et al.
(författare)
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SKS splitting observations across the Iranian plateau and Zagros: the role of lithosphere deformation and mantle flow
- 2020
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Konferensbidrag (refereegranskat)abstract
- We used more than one decade of core-refracted teleseismic shear (SKS) waveforms recorded atmore than 160 broadband seismic stations across the Iranian plateau and Zagros to investigateseismic anisotropy beneath the region. Splitting analysis of SKS waveforms provides two mainparameters, i.e., fast polarization direction and split delay time, which serve as proxies for thetrend and strength of seismic anisotropy beneath the stations. Our observation revealed acomplex pattern of splitting parameters with variations in the trend and strength of anisotropyacross the tectonic boundaries. We also verified the presence of multiple layers of anisotropy inconjunction with the lithosphere deformation and mantle flow field. Our observation andmodeling imply that a combined system of lithosphere deformation and asthenospheric flow islikely responsible for the observed pattern of anisotropy across the Iranian Plateau and Zagros.The rotational pattern of the fast polarization directions observed locally in Central Zagros mayindicate the diversion of mantle flow around a continental keel beneath the Zagros. Thecorrelation between the variation in lithosphere thickness and the trend of anisotropy in the studyarea implies that the topography of the base of lithosphere is also a determining factor for thepattern of mantle flow inferred from the observations.
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| 9. |
- Nilfouroushan, Faramarz, Senior Lecturer, 1968-, et al.
(författare)
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Analysis of Clay-Induced Land Subsidence in Uppsala City Using Sentinel-1 SAR Data and Precise Leveling
- 2020
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Konferensbidrag (refereegranskat)abstract
- Land subsidence and its subsequent hazardous effects on buildings and urban infrastructure areimportant issues in many cities around the world. The city of Uppsala in Sweden is undergoing significant subsidence in areas that are located on clay. Underlying clay units in parts of Uppsalaact as mechanically weak layers, which for instance, cause sinking of the ground surface and tilting buildings. In this study, a Persistent Scatterer InSAR (PSI) analysis was performed to map theongoing ground deformation in Uppsala. The subsidence rate measured with PSI was validatedwith precise leveling data at different locations. Two ascending and descending data sets wereanalyzed using SARPROZ software, with Sentinel-1 data from the period March 2015 to April 2019.After the PSI analyses, comparative permanent scatterer (PS) points and metal pegs (measuredwith precise leveling) were identified creating validation pairs. According to the PSI analyses,Uppsala was undergoing significant subsidence in some areas, with an annual rate of about 6mm/year in the line-of-sight direction. Interestingly, the areas of great deformation wereexclusively found on postglacial clay.
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| 10. |
- Rashidi, Ahmad, et al.
(författare)
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Morphotectonic and earthquake data analysis of interactional faults in Sabzevaran Area, SE Iran
- 2020
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Ingår i: Journal of Structural Geology. - : Elsevier. - 0191-8141 .- 1873-1201. ; 139
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Tidskriftsartikel (refereegranskat)abstract
- We used satellite images, earthquake catalogues and field observations to study several active fault systems and their interactions in Sabzevaran Area in SE Iran. The focus of this study is to verify the link between the active faults, their kinematics and seismic activity. Field observations and geomorphological analysis highlight the interaction of the active faults. Moreover, most of the tectonic activity is observed in the area, related to the Chahmazrae- North Faryab shear zone. Most of the earthquakes in this shear zone are reverse and occur in the deeper crust while aftershocks dominantly occur in the shallower crust. The Main Zagros Reverse Fault (MZRF) is the source of reverse events and the Chahmazrae- North Faryab shear zone is source of left-lateral, oblique reverse faulting events, and strike-slip events. These types of the earthquakes in the study area confirm the idea of tectonic proximity of the root faults and shear zone. In the interaction area, minor fractures begin to develop and are progressively linked to the main faults. In the en échelon arrangement of the faults, the minor faults have grown and linked the en échelon segments of the faults. It seems that the earthquake ruptures can spontaneously propagate across both extensional and the compressional fault steps. This propagation occurs along strike-slip faults such as Sabzevaran fault and its branches.
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