| 1. |
- 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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| 2. |
- Mehrabi, Ali, et al.
(författare)
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Spatiotemporal subsidence over Pabdana coal mine Kerman Province, central Iran using time-series of Sentinel-1 remote sensing imagery
- 2023
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Ingår i: Episodes. - : International Union of Geological Sciences. - 0705-3797 .- 2586-1298. ; 46:1, s. 19-33
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Tidskriftsartikel (refereegranskat)abstract
- Environmental monitoring of mining regions using satellite imagery is crucial for sustainable exploitation andnpreventing geohazards. Movements due to the failure of the roof in underground coal mining, by migrating upwards and outwards from the seam being mined, could eventually appear as ground deformation. To investigate the matter further, the surface deformation that occurred over the Pabdana mining area was monitored in three time periods, between October 2, 2014, and July 27, 2019. Persistent scatterer interferometry (PSI) was used based on 150 ascending and descending Sentinel-1A images. The maximum mining subsidence rate during the studied periods was about 30 to 35 mm/yr. The PSI analysis shows that the subsidence rate varied both temporally and spatially during the three studied periods. The time series and the displacement rate for various cross-sections highlight a clear quantitative relationship between coal extraction progress and subsidence, which proceeded southward throughout the three study periods. So, considering coal mining subsidence as a geohazard, land developments and structures over the mining area may be safeguarded. The approach used in this investigation can be implemented in other similar coal mining zones.
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| 3. |
- Nilfouroushan, Faramarz, Senior Lecturer, 1968-, et al.
(författare)
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Active and passive radar corner reflectors co-located with permanent GNSS stations in Sweden: Installation and performance
- 2023
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Konferensbidrag (refereegranskat)abstract
- Artificial corner reflectors (CRs), passive (which have no electronic parts), or active ones, so called electronic CR (ECR) or compact transponders (CAT), are devices which reflect the radar signal back to the SAR satellites and provide measurement points at desired locations. Using, such devices we can measure temporal Line of sight (LOS) changes of the CRs using the InSAR technique and for example monitor the ground movements precisely.Since January 2020, Lantmäteriet, the Swedish mapping, cadastral and land registration authority, has installed three ECRs and several types of passive reflectors (different shape and size, planned for C-band Sentinel-1 satellites) in different locations in Sweden. So far, ECRs are still functioning with no electronic failure. However, from the ESA Geodetic SAR project (https://eo4society.esa.int/projects/sar-hsu/) we experienced that the ECRs electronic characteristics are different, so individual calibrations maybe required by the manufacturer. In addition, thermal effects may also cause problems for measurements with ECRs. Therefore, instead of installing more ECRs, we switched to passive ones which have no electronics and have already shown their high-quality performance in different studies. So far, we have installed ten CRs in different locations and the goal is to continue and complement the national geodetic infrastructure of Sweden with at least twenty passive reflectors which are co-located with permanent GNSS stations. Among others, these co-located corner reflectors can potentially contribute to the development of the national and European ground motion services in future updates. Moreover, the co-location helps to map the relative ground motions estimated with InSAR to an absolute geodetic reference frameAmong different tests and performance analysis of such reflectors, we did multipath analysis to investigate if our corner reflectors cause any multipath error on nearby GNSS stations. We looked at the coordinate time series of the twin GNSS stations at two locations, Visby and Sveg. The installed corner reflector, double back-flipped squared, in Sveg is about 6 m away from the GNSS stations whereas, in Visby, the twin corner reflectors, ascending and descending, are about 20 meters away and have a trihedral squared trimmed shape. The daily GNSS coordinate time series for three components before and after installation of the corner reflectors didn’t show any significant jump in the time series and the coordinate variations are in the range of expected mm-level variations for all stations.
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| 4. |
- Nilfouroushan, Faramarz, Senior Lecturer, 1968-, et al.
(författare)
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Activity Report: Contributions from Lantmäteriet to the InSAR-Sweden Project
- 2023
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The two-year Swedish Ground Motion Service (InSAR-Sweden) project was started in 2021 and made a collaboration between the Geological Survey of Norway (NGU) and several Swedish organizations, including Lantmäteriet. During the project, the InSAR-based ground motion service has been developed by NGU using Sentinel-1 data (2015–2021) and the Persistent Scatterer Interferometry (PSI) technique and is freely available for interested users. There were different working groups in the project and Lantmäteriet has contributed mostly to working group WP#3 which is the “validation of deformation data”.We used the PSI results of previous studies for Uppsala and Gävle cities to validate the newly launched InSAR-Sweden ground motion service. We compared the deformation localization and Line of Sight (LOS) displacement time series at some deforming locations. Although the number and acquisition dates of Sentinel-1 data and the parameters used for PSI processing differ between Uppsala, Gävle and InSAR-Sweden, the cross-checked results demonstrate good agreement between corresponding studies regarding the localization and rate of subsidence in those two cities over a period of five years.During the project, Lantmäteriet installed several types of radar corner reflectors (CR) in different locations in Sweden. These corner reflectors are passive devices which provide precise measurement points and can be installed at desired locations. These devices can be used to measure temporal LOS changes and consequently the ground movements precisely using the InSAR technique. The plan is to continue and complement the national geodetic infrastructure with at least 20 passive reflectors which are collocated with permanent GNSS stations and/or tide gauges. Among others, these co-located permanent GNSS stations and corner reflectors can potentially contribute to the development and validation of the national (InSAR-Sweden) and European ground motion (EGMS) services. Moreover, the co-location helps to transform the relative ground motions estimated with InSAR to an absolute geodetic reference frame.In this activity report, we provide a brief introduction to SAR corner reflectors and their applications, and we explain our progress in installing such reflectors in Sweden. We also present our preliminary results from our data analysis. Moreover, we explain our cross-checking of the results obtained from InSAR-Sweden with the InSAR-based studies conducted for Uppsala and Gävle cities.
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| 5. |
- Nilfouroushan, Faramarz, Senior Lecturer, 1968-, et al.
(författare)
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SAR Reflektorer och deras tillämpningar i Geodetiskinfrastruktor: En Lägesrapport om installation av passiva Reflektorer i Sverige
- 2023
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Konferensbidrag (refereegranskat)abstract
- Intresset för att använda Interferometric Synthetic Aperture Radar (InSAR) förmarkrörelseövervakning ökar snabbt, tack vare de fritt tillgängliga CopernicusSentinel-1 satellitbilderna som täcker relativt stora områden med en återbesökstidpå 12 dagar. För att etablera en specifik mätpunkt på en önskad platsanvänds artificiella SAR-reflektorer. Dessa är passiva enheter som ger exaktamätpunkter och kan vara användbara för många tillämpningar inklusivemarkrörelseövervakning med InSAR-tekniken. Sedan 2021 har Lantmäterietinstallerat flera typer av så kallade kubhörnreflektorer på olika platser i Sverigeför att komplettera den nationella geodetiska infrastrukturen. Dessa är samlokaliserademed SWEPOS permanenta GNSS-stationer och kan potentielltbidra till utvecklingen och valideringen av de nationella (InSAR-Sverige) ocheuropeiska (EGMS) markrörelsetjänsterna. Dessutom skapar samlokaliseringenförutsättningar för transformation av de relativa markrörelserna uppskattademed InSAR till ett absolut geodetiskt referenssystem.
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