| 1. |
- Amin, Hadi
(författare)
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Study on the Earth’s Surface Mass Variations using Satellite Gravimetry Observations
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Our complex planet is continuously undergoing temporal and spatial changes. In this context, ongoing processes in the Earth subsystems (geosphere, biosphere, cryosphere, hydrosphere, and atmosphere) cause changes in the gravity field of the Earth across a wide range of temporal and spatial scales. Accordingly, by both spatially and temporally tracing our planet’s ever-changing gravity field, scientists can better constrain the underlying processes contributing to such dynamic changes of mass distribution within the Earth system. Monitoring the Earth’s gravity field and its temporal variations is essential, among others, for tracking disasters and specifying land areas with a high risk of flooding, earthquakes, and droughts, movements of tectonic plates, and providing accurate positioning through satellite positioning technology. On short-term timescales, temporal variations in the Earth’s gravity field are mainly caused by the movement of water in its various forms. Accordingly, sea-level variations and ice-sheet and glacier changes, which are known as critical indicators of global warming and climate change, can be accurately monitored by tracking the Earth’s gravity field changes. Since there is a close link between water redistribution and the Earth’s energy cycle, climate system, food security, human and ecosystem health, energy generation, economic and societal development, and climate extremes (droughts and floods), it is essential to accurately monitor water mass exchange between the Earth system components. Among all observational techniques, satellite gravimetry has provided an integrated global view of ongoing processes within the Earth system. The current generation of satellite gravimetry missions (the Gravity Recovery and Climate Experiment (GRACE) mission and its successor, GRACE Follow-On) has dramatically revolutionized our understanding of dynamic processes in the Earth’s surface and, consequently, has significantly improved our understanding of the Earth’s climate system. By considering different aspects of studying the Earth’s gravity field, this thesis brings new insights to the determination and analysis of the mass change in the Earth system. First, by studying the shortcomings of the common techniques of estimating the geoid potential, a new approach is examined that simultaneously estimates the geoid potential, W0, and the geometrical parameters of the reference Mean Earth Ellipsoid (MEE). In this regard, as the geoid needs to be considered as a static equipotential surface, the sensitivity of the estimations to the time dependent Earth’s gravity field changes is studied. Secondly, relying on the GRACE monthly gravity fields and the complementary observational techniques, and by pushing the limit of GRACE, mass redistribution over land and ocean is investigated. Within the ocean, satellite altimetry and Argo products are utilized along with the GRACE monthly solutions for quantifying the global barystatic sea-level change and assessing the closure of the global mean sea level budget. Over land, a region with relatively high temporal mass change (oil and water extraction) is chosen in which by taking advantage of having in-situ observations and hydrological models, the ability of GRACE products in quantifying the changes in groundwater storage is studied. In this frame, for both the ocean and land studies, different aspects of the processing of GRACE monthly gravity fields are investigated and GRACE inherent errors are addressed appropriately to arrive at reliable and accurate estimates of the Earth’s surface mass change. As the final contribution in this thesis, a rigorous analytical model for detecting surface mass change from the time-variable gravity solutions is proposed and examined in different case studies of surface mass change. Since the launch of the GRACE twin satellites, the GRACE(-FO) time-varying gravity fields are conventionally converted into the surface mass change using a spherical analytical model that approximates the Earth by a sphere. More recently, the analytical mass change detection model has been improved by considering an ellipsoid as the shape of the Earth, which improved the previous estimations of surface mass change, especially over high latitudes with relatively large mass change signals. However, by taking into account the real shape of the Earth and considering more realistic assumptions, a new analytical solution for the problem of surface mass change detection from the time-varying gravity fields is proposed in this thesis. It is shown that the simplistic spherical and ellipsoidal geometries are no longer tenable and the new model surpasses the common spherical approach and its ellipsoidal version.
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| 2. |
- Bagherbandi, Mohammad, Professor, et al.
(författare)
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Deflection of Vertical Effect on Direct Georeferencing in Aerial Mobile Mapping Systems : A Case Study in Sweden
- 2022
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Ingår i: Photogrammetric Record. - : Wiley. - 0031-868X .- 1477-9730. ; 37:179, s. 285-305
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Tidskriftsartikel (refereegranskat)abstract
- GNSS/INS applications are being developed, especially for direct georeferencing in airborne photogrammetry. Achieving accurately georeferenced products from the integration of GNSS and INS requires removing systematic errors in the mobile mapping systems. The INS sensor's uncertainty is decreasing; therefore, the influence of the deflection of verticals (DOV, the angle between the plumb line and normal to the ellipsoid) should be considered in the direct georeferencing. Otherwise, an error is imposed for calculating the exterior orientation parameters of the aerial images and aerial laser scanning. This study determines the DOV using the EGM2008 model and gravity data in Sweden. The impact of the DOVs on horizontal and vertical coordinates, considering different flight altitudes and camera field of view, is assessed. The results confirm that the calculated DOV components using the EGM2008 model are sufficiently accurate for aerial mapping system purposes except for mountainous areas because the topographic signal is not modelled correctly.
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| 3. |
- Bagherbandi, Mohammad, Professor, et al.
(författare)
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Importance of precise gravity field modeling in direct georeferencing and aerial photogrammetry : a case study for Sweden
- 2022
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Ingår i: The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XLIII-B2-2022XXIV ISPRS Congress (2022 edition), 2022, Vol. XLIII-B2. - : International Society for Photogrammetry and Remote Sensing. ; , s. 15-20
-
Konferensbidrag (refereegranskat)abstract
- Direct georeferencing of airborne mobile mapping systems is developing with unprecedented speed using GNSS/INS integration. Removal of systematic errors is required for achieving a high accurate georeferenced product in mobile mapping platforms with integrated GNSS/INS sensors. It is crucial to consider the deflection of verticals (DOV) in direct georeferencing due to the recently improved INS sensor accuracy. This study determines the DOV using Sweden's EGM2008 model and gravity data. The influence of the DOVs on horizontal and vertical coordinates and considering different flight heights is assessed. The results confirm that the calculated DOV components using the EGM2008 model are sufficiently accurate for aerial photogrammetry purposes except for the mountainous areas because the topographic signal is not modeled correctly.
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| 4. |
- Darvishi, Mehdi, et al.
(författare)
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InSAR-based Ground Motion Service of Sweden: evaluation and benefit analysis of a nationwide InSAR service
- 2022
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Konferensbidrag (refereegranskat)abstract
- Space-geodetic techniques such as Global Navigation Satellite Systems (GNSS) and Syntenic Aperture Radar interferometry (InSAR) are powerful tools to measure and monitor ground surface motion. InSAR has widely been used for the detection and quantification of slow mass movements over the past three decades mainly at the local and regional scales. The high performance and millimeter-level measurement accuracy of radar satellite to provide a dense deformation map at different spatial and temporal resolutions are the key factors to think of using SAR data and InSAR technique as an efficient tool for geohazards motoring system at the nationwide scale.Sweden has recently joined to the countries having InSAR Ground Motion Service (GMS) at a nationwide scale. The InSAR service of Sweden, which will soon be freely available for users, provides the displacement time-series of measurement points for the entire country. The Swedish GMS project was started last year and is an ongoing collaboration between the Geological Survey of Norway (NGU) and several Swedish organizations (led by the Swedish National Space Agency (SNSA)). The InSAR-based GMS of Sweden has been generated by NGU using Sentinel-1 data (2015–2020) and the Persistent Scatterer Interferometry (PSI) technique. The web-based GMS of Sweden consists of ~1,5 billion time-series measurement points obtained from both descending and ascending satellite orbital modes.Currently, the Swedish GMS is under evaluation and validation phase and the given plan has been designed to assess the quality or validate the GMS products. We plan to conduct the data validation through two main phases: 1) a cross-comparison between InSAR measurement points and ancillary data such as GNSS, Corner Reflectors (CR), Electronic Corner Reflectors (ECR) and leveling data, and 2) assessment of tropospheric and ionospheric effects on InSAR measurement points. Specifically, we will evaluate different approaches and data for the InSAR tropospheric corrections, such as Very-Long-Baseline Interferometry (VLBI), Water Vapour Radiometry (WVR), and GNSS data at the Onsala Space Observatory (OSO).In the first phase of validation, leveling data collected in Gothenburg and Stockholm cities, mainly over the residential areas and public transport infrastructures compared to the corresponding InSAR measurements points (vertically converted) for a five-year period. The initial results present a high correlation between two sets of the vertical displacements. The same procedure will be performed for the Kiruna city where the mining activities resulted in adrastic urban land subsidence. Since the CRs and ECRs have recently been installed in different parts of Sweden, we do not have them as PS points in the current version of the GMS. Therefore, those CR-based measurement points will be used in future accuracy assessments. In the second phase, we investigated the effects of phase delay induced by troposphere on displacement time-series using two approaches, i.e., time-space filtering and using external data (e.g., atmospheric reanalysis data, GNSS, VLBI and Water Vapor Radiometer (WVR)). Recently, European GMS (EGMS) has been released and the Ortho displacement map is now available for users freely. We also evaluated and compared the EGMS-Ortho displacement map with our independent InSAR processing and GNSS data over the Kiruna.As the InSAR-based GMS can be used to monitor and identify the potential risk of geo-related hazards in Sweden, the society will directly benefit from the outcomes of this project. This open access product will help the stakeholders with decision support for prioritization of risk-reducing measures, and identification of the need for further investigations for areas in danger. The service could also assist municipalities and county administrative boards to have an update information regarding urban areas which are more prone to land subsidence and disruption urban infrastructure.
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| 5. |
- 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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| 6. |
- 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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| 7. |
- Fryksten, Jonas, et al.
(författare)
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Analysis of Clay-Induced Land Subsidence in Uppsala City Using Sentinel-1 SAR Data and Precise Leveling
- 2019
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Ingår i: Remote Sensing. - : MDPI. - 2072-4292. ; 11:23
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Tidskriftsartikel (refereegranskat)abstract
- Land subsidence and its subsequent hazardous effects on buildings and urban infrastructure are important 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 Uppsala act as mechanically weak layers, which for instance, cause sinking of the ground surface and tilting buildings. Interferometric Synthetic Aperture Radar (InSAR) has given rise to new methods of measuring movements on earth surface with a precision of a few mm. In this study, a Persistent Scatterer InSAR (PSI) analysis was performed to map the ongoing ground deformation in Uppsala. The subsidence rate measured with PSI was validated with precise leveling data at different locations. Two ascending and descending data sets were analyzed 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 (measured with 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 6 mm/year in the line-of-sight direction. Interestingly, the areas of great deformation were exclusively found on postglacial clay.
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| 8. |
- 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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| 9. |
- 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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| 10. |
- 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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| 11. |
- Gruber, Thomas, et al.
(författare)
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Geodetic SAR for Baltic Height System Unification and Baltic Sea Level Research
- 2021
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Rapport (refereegranskat)abstract
- Traditionally, sea level is observed at tide gauge stations, which usually also serve as height reference stations for national levelling networks and therefore define a height system of a country. Thus, sea level research across countries is closely linked to height system unification and needs to be regarded jointly. The project aims to make use of a new observation technique, namely SAR positioning, which can help to connect the GNSS basic network of a country to tide gauge stations and as such to link the sea level records of tide gauge stations to the geometric network. By knowing the geoid heights at the tide gauge stations in a global height reference frame with high precision, one can finally obtain absolute sea level heights of the tide gauge stations in a common reference system and can link them together. By this method, on the one hand national height systems can be connected and on the other hand the absolute sea level at the tide gauge stations can be determined. By analysing time series of absolute sea level heights their changes can be determined in an absolute sense in a global reference frame and the impact of climate change on sea level can be quantified (e.g. by ice sheet and glacier melting, water inflow, global warming). The major scientific challenges to be addressed by this project then can be summarized as follows: (1) Connection of the tide gauge markers with the GNSS network geometrically in order to determine the relative vertical motion and to correct the tide gauge readings. For this the new technique of SAR positioning is applied. (2) Determination of a GOCE based high resolution geoid at tide gauge stations in order to deliver absolute heights of tide gauges with respect to a global equipotential surface as reference. (3) Joint analysis of geometrical and physical reference frames to make them compatible, and to determine corrections to be applied for combined analysis of geometric and physical heights.
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| 12. |
- 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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| 13. |
- Gruber, T, et al.
(författare)
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Geodetic SAR for Height System Unification and Sea Level Research - Observation Concept and Results in the Baltic Sea
- 2021
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Konferensbidrag (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. Thus, sea level research across countries is closely linked to height system unification and needs to be regarded jointly. 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 permanent GNSS receivers next to the tide gauge in order to systematically observe vertical land motion. 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 results for a test network in the Baltic sea area by combining geometric and physical heights with tide gauge readings.
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| 14. |
- Gruber, Thomas, et al.
(författare)
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Geodetic SAR for Height System Unification and Sea Level Research - Observation Concept and Results in the Baltic Sea
- 2022
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Konferensbidrag (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. Thus, sea level research across countries is closely linked to height system unification and needs to be regarded jointly. 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 permanent GNSS receivers next to the tide gauge in order to systematically observe vertical land motion. 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.The paper presents the results of a project, which was conducted in the years 2019 to 2021 in the frame of ESA´s Baltic+ initiative. Within this project a test network of electronic corner reflectors (ECR) as targets for Sentinel-1 was realized in the Baltic Sea area. The ECR locations were either co-located with tide gauges or with permanent GNSS stations in order to observe systematically the ellipsoidal heights of the tide gauges and possibly also any vertical land motion at the stations. Data for the year 2020 were collected at 10 stations in Estonia, Finland, Poland and Sweden and jointly analyzed with GNSS data, tide gauge records and regional geoid height estimates. The obtained results are promising, but also exhibit some problems related to the ECR´s and their performance. At co-located GNSS stations the estimated ellipsoidal heights agree in a range between about 2 and 50 cm between both observation systems. From the results it could be identified that most likely variable systematic electronic instrument delays of the ECR´s are the main reason for these differences and that each instrument needs to be calibrated individually. Nevertheless, the project provides a valuable data set, which offers the possibility to enhance methods and procedures in order to develop the geodetic SAR positioning technique towards operability. All data and reports are accessible at the following web site: https://www.asg.ed.tum.de/iapg/baltic/
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| 15. |
- Jivall, Lotti, et al.
(författare)
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Analysis of 20 years of GPS data from SWEREF consolidation points – using BERNESE and GAMIT-GLOBK software
- 2022
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Rapport (populärvet., debatt m.m.)abstract
- The SWEREF 99 national geodetic reference frame has been used in Sweden since 2007 and it was adopted by EUREF in 2000 as the national realisation of ETRS89 in Sweden [Jivall and Lidberg, 2000]. The SWEREF 99 reference frame is defined by an active approach through the 21 original (fundamental) SWEPOS GNSS stations, hence relying on positioning services such as the network real time kinematic (NRTK) and post processing services. The SWEREF 99 coordinates are assumed to be fixed in time and no temporal variations are expected. However, the stability of the stations and their coordinates can be altered due to equipment change or software as well as local movements at the reference stations.To be able to check all alterations mentioned above and having a backup national network of GNSS points, approximately 300 passive so-called consolidation points are used. The consolidation points are a subset (the main part) of the so-called SWEREF points established from 1996 and onwards. All 300 points are remeasured with static GNSS for 2x24 hours using choke ring antennas on a yearly basis with 50 points each year. The original data processing was done with the Bernese GNSS software in a regular basis and the reprocessing was carried out with both the Bernese and the GAMIT-GLOBK software packages during 2017-2018.The resulting coordinates in SWEREF 99 from GAMIT and Bernese processing are equal at 1–2 mm level for the horizontal and 4 mm for the vertical components (1 sigma) when using almost the same models and processing strategy. The result from the original processing, which partly is based on other models and parameters, differs slightly more for the north component compared to the reprocessing results (RMS of 2 mm compared to 1 mm).Our analysis both of Bernese and GAMIT results shows that the standard uncertainties for a single SWEREF 99 coordinate determination (with 2x24 hrs observation) is about 2 mm for the horizontal components and 6 mm in height. It is interesting to note that the coordinate repeatability is on the same level also for the original processing, where we have differences in models and parameters used during the years. This indicates that our concept for determining SWEREF 99 coordinates has worked well on the mentioned uncertainty level.We performed trend analysis and statistical tests for the points having minimum three observations to investigate the stability of the estimated SWEREF 99 coordinates. The low rate of redundancy (just one redundant observation in case of three observations) was a problem so a modified version of the F-test was developed which gave good agreement with visual interpretation of the time series. This strategy showed that about 10% of the points had trends (with notable movements), but we should be aware of the low redundancy. With more observations in the future, we can determine trends more reliably.We will continue to analyse the point coordinate repeatability and trends when we get more data. Further on, some reprocessing is needed to be compatible with the SWEREF 99 update 2021 at SWEPOS. We will also study the effect of using different satellite systems and finally prepare for the publication of updated coordinates in the Digital Geodetic Archive (DGA) provided by Lantmäteriet.
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| 16. |
- Jivall, Lotti, et al.
(författare)
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Mast-based versus Pillar-based Networks for Coordinate Estimation of SWEREF points : – using the Bernese and GAMIT-GLOBK Software Packages
- 2015
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- For about 20 years, the fundamental pillar stations in SWEPOS network (the Swedish Permanent GNSS network) have been used as the carrier of the Swedish national reference frame, SWEREF 99, and used as control points for several geodetic and geodynamic studies. Today, each pillar station has a close-by truss mast station, mostly in 10 meters distance. Switching from pillar-based network to mast-based network (with stations equipped with more modern receivers and calibrated antennas), as reference network,need careful analysis, for example, comparing solutions from these networks. In this study, we use both the Bernese GNSS Software (BSW) and GAMIT-GLOBK softwareand process the same data set with almost the same processing strategy and compare the results. Our solutions and their comparisons show that BSWhas slightly lower rate of resolved integer ambiguities for the mast-basednetwork compared to the pillar-basednetwork (3-4percentage pointsfor the selected 14 SWEREF points and 1-2percentage pointsfor all SWEREFpoints (50) processed in this study).For GAMIT-GLOBK, we don’tsee any significant difference in the rate of resolved integer ambiguities between the network types.Furthermore, the comparison of resulting coordinates between the two software, show avery good compliancefor the pillar-based network (on average at the 1 mm level for the horizontal components and 2 mm for the height component), but for the mast-based network there is 3-4 mm systematic difference in the height component.The good compliance between the GAMIT-GLOBK and BSW solutions for the pillar network,makes it possible to use results also from GAMIT-GLOBK for coordinate determination of SWEREF points. The systematic height difference between the two software solutions for the mast-based network,as well as slightly degraded quality measures mainlyfor BSW,indicate that there are some problems with the mast stations that need further investigation.
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| 17. |
- 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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| 18. |
- Jouybari, Arash, et al.
(författare)
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Comparison of the strip- and block-wise aerial triangulation using different exterior orientation parameters weights
- 2021
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Ingår i: Journal of Spatial Information Science. - : Informa UK Limited. - 1948-660X .- 1449-8596 .- 1836-5655. ; , s. 1-18
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Tidskriftsartikel (refereegranskat)abstract
- In this study, three different procedures: checkpoint RMS of residuals, statistical evaluation of AT results using t-test, and comparison of a photogrammetric digital surface model (DSM) and LiDAR data are used to analyse the effect of IMU and GNSS uncertainties on the final adjusted results. The outcome suggests that the method of block-wise GNSS shift correction is the better method for aerial triangulation and one should use appropriate observable weights in AT. The comparison of checkpoint RMS residuals between the two methods shows that the block-wise solution is on average 6cm more accurate than the strip-wise solution.
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| 19. |
- Jouybari, Arash, et al.
(författare)
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Impact of GNSS Signal outage on EOPs using forward Kalman filter and smoothing algorithm
- 2022
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Ingår i: 2022 | XXIV ISPRS Congress “Imaging today, foreseeing tomorrow”, Commission II. - : Copernicus GmbH. ; , s. 59-64, s. 59-64
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Konferensbidrag (refereegranskat)abstract
- The global navigation satellite system (GNSS) has been playing the principal role in positioning applications in past decades. Position robustness degrades with a standalone receiver due to GNSS signal outage in mobile mapping systems. The GNSS and inertial measurement unit (IMU) integration is used to solve positioning degradation. This article studies the GNSS/IMU integration processing (i.e., forward Kalman filter (KF) and smoothing algorithm) using a single or a network of nearby GNSS reference stations. In addition, we analyze the impact of simulated GNSS signal outage on exterior orientation parameters (EOPs). The outcomes confirm that the smoothing algorithm works better than the forward KF and improves the accuracy for position and orientation in the case when there is no GNSS signal outage. Also, it improves the position and orientation accuracy by about 95% and 60% when there is a 180 second GNSS signal outage, respectively.
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| 20. |
- Jouybari, Arash, et al.
(författare)
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Numerical Analysis of GNSS Signal Outage Effect on EOPs Solutions Using Tightly Coupled GNSS/IMU Integration : A Simulated Case Study in Sweden
- 2023
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Ingår i: Sensors. - : MDPI AG. - 1424-8220. ; 23:14
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Tidskriftsartikel (refereegranskat)abstract
- The absence of a reliable Global Navigation Satellite System (GNSS) signal leads to degraded position robustness in standalone receivers. To address this issue, integrating GNSS with inertial measurement units (IMUs) can improve positioning accuracy. This article analyzes the performance of tightly coupled GNSS/IMU integration, specifically the forward Kalman filter and smoothing algorithm, using both single and network GNSS stations and the post-processed kinematic (PPK) method. Additionally, the impact of simulated GNSS signal outage on exterior orientation parameters (EOPs) solutions is investigated. Results demonstrate that the smoothing algorithm enhances positioning uncertainty (RMSE) for north, east, and heading by approximately 17-43% (e.g., it improves north RMSE from 51 mm to a range of 42 mm, representing a 17% improvement). Orientation uncertainty is reduced by about 60% for roll, pitch, and heading. Moreover, the algorithm mitigates the effects of GNSS signal outage, improving position uncertainty by up to 95% and orientation uncertainty by up to 60% using the smoothing algorithm instead of the forward Kalman filter for signal outages up to 180 s.
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| 21. |
- Kaviani, A., et al.
(författare)
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Complex pattern of seismic anisotropy beneath the Iranian plateau and Zagros
- 2019
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Konferensbidrag (refereegranskat)abstract
- We performed shear wave splitting analyses on core-refracted teleseismic shear waveforms from 150 broad-bandstations across the Iranian plateau and Zagros to investigate seismic anisotropy in the region. Seismic anisotropyis quantified by shear-wave splitting parameters, i.e. fast polarization direction and split delay time.Our measurements revealed a complex pattern of splitting parameters with variations in the trend and strength ofanisotropy across the tectonic boundaries. This complex pattern implies that a system of simple asthenosphericflow related to the absolute plate motion cannot alone explain our observations and that the lithosphere also hasa significant contribution in many parts. We compare our results to the surface deformation and velocity fieldsinferred from geodetic measurements to assess the role of the mantle in continental deformation. The rotationalpattern of the fast directions around the collision zone in Central Zagros may indicate the presence of a mantleflow around a continental keel beneath the Zagros. The agreement between the crustal and mantle deformationfield in Central Iran implies a vertically coherent deformation in this region, whereas the azimuthal variations insplitting parameters in the collision zone may suggest multi-layered anisotropy with different contributions fromthe crust and mantle.
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| 22. |
- Kaviani, Ayoub, et al.
(författare)
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Mantle-flow diversion beneath the Iranian plateau induced by Zagros’ lithospheric keel
- 2021
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Ingår i: Scientific Reports. - : Nature. - 2045-2322. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- Previous investigation of seismic anisotropy indicates the presence of a simple mantle flow regime beneath the Turkish-Anatolian Plateau and Arabian Plate. Numerical modeling suggests that this simple flow is a component of a large-scale global mantle flow associated with the African superplume, which plays a key role in the geodynamic framework of the Arabia-Eurasia continental collision zone. However, the extent and impact of the flow pattern farther east beneath the Iranian Plateau and Zagros remains unclear. While the relatively smoothly varying lithospheric thickness beneath the Anatolian Plateau and Arabian Plate allows progress of the simple mantle flow, the variable lithospheric thickness across the Iranian Plateau is expected to impose additional boundary conditions on the mantle flow field. In this study, for the first time, we use an unprecedented data set of seismic waveforms from a network of 245 seismic stations to examine the mantle flow pattern and lithospheric deformation over the entire region of the Iranian Plateau and Zagros by investigation of seismic anisotropy. We also examine the correlation between the pattern of seismic anisotropy, plate motion using GPS velocities and surface strain fields. Our study reveals a complex pattern of seismic anisotropy that implies a similarly complex mantle flow field. The pattern of seismic anisotropy suggests that the regional simple mantle flow beneath the Arabian Platform and eastern Turkey deflects as a circular flow around the thick Zagros lithosphere. This circular flow merges into a toroidal component beneath the NW Zagros that is likely an indicator of a lateral discontinuity in the lithosphere. Our examination also suggests that the main lithospheric deformation in the Zagros occurs as an axial shortening across the belt, whereas in the eastern Alborz and Kopeh-Dagh a belt-parallel horizontal lithospheric deformation plays a major role.
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| 23. |
- 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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| 24. |
- Khorrami, F., et al.
(författare)
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An up-to-date block model and strain rate map of Iran using integrated campaign-mode and permanent GPS velocities
- 2019
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Ingår i: 27th IUGG General Assembly.
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Konferensbidrag (refereegranskat)abstract
- Iran accommodates a large part of the ongoing Arabia-Eurasia collision deformation. Because of such active tectonics, the country suffers from intensive seismicity and frequent destructive earthquakes in different locations.To study further the crustal deformation in Iran, we processed the data collected during 10 years (2006-2015) from the Iranian Permanent GNSS Network and combined them with previously published velocity solutions from GPS survey measurements during 1997–2013. We analysed this velocity field using a continuum approach to compute a new strain rate map for this region and we designed a block model based on the main geological, morphological, and seismic structures. Comparison between both approaches suggests similar results and allow us to present the first comprehensive first order fault slip rate estimates for the whole of Iran. Our results confirm most of the results from previous geodetic studies. Moreover, we also show a trade-off between the coupling ratio of the Iranian Makran subduction interface and the kinematic of the faults north of the Makran in the Jazmurian depression. Although too scarce to accurately estimate a coupling ratio, we show that coupling higher than 0.4 on the plate interface down to a depth of 25 km will induce extension on the E-W faults in the Jazmurian region. However, the sites close to the shoreline suggest a low coupling ratio, hence the coupling on this plate interface is probably more complicated than previously described and the Iranian Makran subduction interface mechanical behaviour might be similar to that on the Hellenic subduction zone.
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| 25. |
- Khorrami, Fatemeh, et al.
(författare)
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An up-to-date crustal deformation map of Iran using integrated campaign-mode and permanent GPS velocities
- 2019
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Ingår i: Geophysical Journal International. - : Oxford University Press. - 0956-540X .- 1365-246X. ; 217:2, s. 832-843
-
Tidskriftsartikel (refereegranskat)abstract
- We present the most extensive and up-to-date unified GPS velocity field for Iran. We processed the data collected during 10 years (2006–2015) from the Iranian Permanent GNSS Network (IPGN) and combined them with previously published velocity solutions from GPS survey measurements during 1997–2013. We analysed this velocity field using a continuum approach to compute a new strain rate map for this region and we designed a block model based on the main geological, morphological, and seismic structures. Comparison between both approaches suggests similar results and allow us to present the first comprehensive first order fault slip rate estimates for the whole of Iran. Our results confirm most of the results from previous geodetic studies. But we also show a trade-off between the coupling ratio of the Iranian Makran subduction interface and the kinematic of the faults north of the Makran in the Jazmurian depression. Indeed, although too scarce to accurately estimate a coupling ratio, we show that coupling higher than 0.4 on the plate interface down to a depth of 25 km will induce extension on the E-W faults in the Jazmurian region. However, the sites close to the shoreline suggest a low coupling ratio, hence the coupling on this plate interface is probably more complicated than previously described and the Iranian Makran subduction interface mechanical behaviour might be similar to that on the Hellenic subduction zone.
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