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Nilfouroushan, Faramarz, Senior LecturerORCID iD iconorcid.org/0000-0003-1744-7004
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Publications (10 of 79) Show all publications
Nilfouroushan, F., Gido, N., Olsson, P.-A. & Puwakpitiya Gedara, C. (2023). Active and passive radar corner reflectors co-located with permanent GNSS stations in Sweden: Installation and performance. In: : . Paper presented at EGU General Assembly 2023, Vienna, Austria & Online, 23–28 April 2023.
Open this publication in new window or tab >>Active and passive radar corner reflectors co-located with permanent GNSS stations in Sweden: Installation and performance
2023 (English)Conference paper, Poster (with or without abstract) (Refereed)
Abstract [en]

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 frame

Among 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.

Keywords
InSAR, deformation, remote sensing, subsidence, Ground motion, validation, corner reflector
National Category
Engineering and Technology Earth and Related Environmental Sciences Natural Sciences
Identifiers
urn:nbn:se:hig:diva-41115 (URN)
Conference
EGU General Assembly 2023, Vienna, Austria & Online, 23–28 April 2023
Available from: 2023-02-23 Created: 2023-02-23 Last updated: 2023-02-24Bibliographically approved
Nilfouroushan, F., Gido, N., Olsson, P.-A. & Gedara, C. P. (2023). Activity Report: Contributions from Lantmäteriet to the InSAR-Sweden Project. Gävle: Lantmäteriet
Open this publication in new window or tab >>Activity Report: Contributions from Lantmäteriet to the InSAR-Sweden Project
2023 (English)Report (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Gävle: Lantmäteriet, 2023. p. 40
Series
Lantmäterirapport - Geodetic Report, ISSN 0280-5731 ; 1
Keywords
InSAR, deformation, remote sensing, subsidence, Ground motion, validation, corner reflectors
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:hig:diva-41126 (URN)
Available from: 2023-02-24 Created: 2023-02-24 Last updated: 2023-03-10Bibliographically approved
Jouybari, A., Bagherbandi, M. & Nilfouroushan, F. (2023). Numerical Analysis of GNSS Signal Outage Effect on EOPs Solutions Using Tightly Coupled GNSS/IMU Integration: A Simulated Case Study in Sweden. Sensors, 23(14), Article ID 6361.
Open this publication in new window or tab >>Numerical Analysis of GNSS Signal Outage Effect on EOPs Solutions Using Tightly Coupled GNSS/IMU Integration: A Simulated Case Study in Sweden
2023 (English)In: Sensors, E-ISSN 1424-8220, Vol. 23, no 14, article id 6361Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
MDPI, 2023
Keywords
GNSS/INS integration; forward Kalman filter; smoothing algorithm; tightly coupled; PPK; virtual reference station; aerial photogrammetry
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:hig:diva-42795 (URN)10.3390/s23146361 (DOI)001039024700001 ()37514655 (PubMedID)2-s2.0-85166022553 (Scopus ID)
Available from: 2023-08-01 Created: 2023-08-01 Last updated: 2023-11-23Bibliographically approved
Nilfouroushan, F., Gido, N., Olsson, P.-A. & Puwakpitiya Gedara, C. (2023). SAR Reflektorer och deras tillämpningar i Geodetiskinfrastruktor: En Lägesrapport om installation av passiva Reflektorer i Sverige. In: : . Paper presented at Kartdagarna 2023, Helsingborg 18-20 april 2023.
Open this publication in new window or tab >>SAR Reflektorer och deras tillämpningar i Geodetiskinfrastruktor: En Lägesrapport om installation av passiva Reflektorer i Sverige
2023 (Swedish)Conference paper, Oral presentation with published abstract (Refereed)
Abstract [sv]

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.

Keywords
InSAR, deformation, remote sensing, subsidence, Ground motion, validation
National Category
Environmental Engineering Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:hig:diva-41116 (URN)
Conference
Kartdagarna 2023, Helsingborg 18-20 april 2023
Available from: 2023-02-23 Created: 2023-02-23 Last updated: 2023-02-24Bibliographically approved
Mehrabi, A., Derakhshani, R., Nilfouroushan, F., Rahnamarad, J. & Azarafza, M. (2023). Spatiotemporal subsidence over Pabdana coal mine Kerman Province, central Iran using time-series of Sentinel-1 remote sensing imagery. Episodes, 46(1), 19-33
Open this publication in new window or tab >>Spatiotemporal subsidence over Pabdana coal mine Kerman Province, central Iran using time-series of Sentinel-1 remote sensing imagery
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2023 (English)In: Episodes, ISSN 0705-3797, Vol. 46, no 1, p. 19-33Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
International Union of Geological Sciences, 2023
Keywords
InSAR, Minning, deformation, remote sensing, subsidence
National Category
Remote Sensing
Identifiers
urn:nbn:se:hig:diva-38157 (URN)10.18814/epiiugs/2022/022009 (DOI)001043375100002 ()2-s2.0-85149281578 (Scopus ID)
Available from: 2022-03-16 Created: 2022-03-16 Last updated: 2023-08-24Bibliographically approved
Jivall, L., Nilfouroushan, F. & Al Munaizel, N. (2022). Analysis of 20 years of GPS data from SWEREF consolidation points – using BERNESE and GAMIT-GLOBK software. Lantmäteriet
Open this publication in new window or tab >>Analysis of 20 years of GPS data from SWEREF consolidation points – using BERNESE and GAMIT-GLOBK software
2022 (English)Report (Other (popular science, discussion, etc.))
Abstract [en]

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.

Place, publisher, year, edition, pages
Lantmäteriet, 2022. p. 84
Series
Lantmäterirapport ; 1
Keywords
GPS, SWEREF 99, reference frame, geodesy, Swedden
National Category
Geosciences, Multidisciplinary
Identifiers
urn:nbn:se:hig:diva-40066 (URN)10.13140/RG.2.2.25918.97609 (DOI)
Available from: 2022-10-05 Created: 2022-10-05 Last updated: 2022-10-11Bibliographically approved
Shami, S., Khoshlahjeh Azar, M., Nilfouroushan, F., Salimi, M. & Reshadi, M. A. (2022). Assessments of ground subsidence along the railway in the Kashan plain, Iran, using Sentinel-1 data and NSBAS algorithm. International Journal of Applied Earth Observation and Geoinformation, 112, Article ID 102898.
Open this publication in new window or tab >>Assessments of ground subsidence along the railway in the Kashan plain, Iran, using Sentinel-1 data and NSBAS algorithm
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2022 (English)In: International Journal of Applied Earth Observation and Geoinformation, ISSN 1569-8432, E-ISSN 1872-826X, Vol. 112, article id 102898Article in journal (Refereed) Published
Abstract [en]

The 110-kilometer-long Qom-Kashan railway is one of the busiest lines in Iran, passing through the Kashan plain. The majority of Iran's plains have subsided in recent years as a result of uncontrolled groundwater extraction, and the Kashan plain is no exception. In this study, ground surface displacement in the Kashan plain region and its impact on the railway were investigated using New Small Baseline Subset (NSBAS) in up-down and east–west directions using descending and ascending Sentinel-1 data collected between 2015 and 2021. Our results indicate that the Kashan plain is subsiding more than 90 mm/year. The study of the local areas around the railway which passes through the study area revealed that the rate of vertical velocity in some locations reaches –23 mm/year, while the rate of east–west velocity is insignificant and is approximately ±2 mm/year. Additionally, a method for analyzing the railway's stability based on longitudinal profiles along the railway is presented. Our findings suggest that more than 60% of the railway line is subject to variable amounts of subsidence. Additionally, a region of approximately one kilometer of the railway has been classified as a risk zone due to relatively fast local deformation. After examining the effect of various factors, it was determined that uncontrolled groundwater extraction in agricultural areas contributed to the subsidence in this area. Our results show that the presented stability control approach in this study is highly reliable for creating hazard profiles for linear structures, such as railways.

Place, publisher, year, edition, pages
Elsevier, 2022
Keywords
Railway, Subsidence, Railway stability, InSAR, Sentinel-1, NSBAS, Kashan, Iran
National Category
Remote Sensing Environmental Management Other Environmental Engineering
Identifiers
urn:nbn:se:hig:diva-39403 (URN)10.1016/j.jag.2022.102898 (DOI)000844329400002 ()2-s2.0-85133391758 (Scopus ID)
Available from: 2022-07-01 Created: 2022-07-01 Last updated: 2022-11-16Bibliographically approved
Jouybari, A., Bagherbandi, M. & Nilfouroushan, F. (2022). Comparison of the strip- and block-wise aerial triangulation using different exterior orientation parameters weights. Journal of Spatial Science, 67(3), 377-394
Open this publication in new window or tab >>Comparison of the strip- and block-wise aerial triangulation using different exterior orientation parameters weights
2022 (English)In: Journal of Spatial Science, ISSN 1449-8596, Vol. 67, no 3, p. 377-394Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Taylor & Francis, 2022
Keywords
Photogrammetry, Direct georeferencing, INS/GNSS Integration
National Category
Geosciences, Multidisciplinary
Identifiers
urn:nbn:se:hig:diva-35211 (URN)10.1080/14498596.2020.1871086 (DOI)000614777300001 ()2-s2.0-85100533681 (Scopus ID)
Available from: 2021-02-04 Created: 2021-02-04 Last updated: 2022-09-21Bibliographically approved
Bagherbandi, M., Jouybari, A., Nilfouroushan, F. & Ågren, J. (2022). Deflection of Vertical Effect on Direct Georeferencing in Aerial Mobile Mapping Systems: A Case Study in Sweden. Photogrammetric Record, 37(179), 285-305
Open this publication in new window or tab >>Deflection of Vertical Effect on Direct Georeferencing in Aerial Mobile Mapping Systems: A Case Study in Sweden
2022 (English)In: Photogrammetric Record, ISSN 0031-868X, E-ISSN 1477-9730, Vol. 37, no 179, p. 285-305Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Wiley, 2022
Keywords
aerial mobile mapping systems, deflection of verticals, direct georeferencing, EGM2008, geoid, photogrammetry
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:hig:diva-39625 (URN)10.1111/phor.12421 (DOI)000829464300001 ()2-s2.0-85134685898 (Scopus ID)
Available from: 2022-07-25 Created: 2022-07-25 Last updated: 2022-12-02Bibliographically approved
Nilfouroushan, F., Gido, N. A. A. & Olsson, P.-A. (2022). Establishment of a new geodetic infrastructure in Sweden using SAR Corner Reflectors: Progress report. In: : . Paper presented at EUREF 2022 SYMPOSIUM, 31 May - 3 June 2022, Zagreb, Croatia.
Open this publication in new window or tab >>Establishment of a new geodetic infrastructure in Sweden using SAR Corner Reflectors: Progress report
2022 (English)Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

Interferometric Synthetic Aperture Radar (InSAR) is a remote sensing and geodetic technique for ground deformation measurements using radar images of the Earth's surface that are collected regularly by orbiting satellites equipped with SAR sensors. Natural reflectors on the ground which backscatter the radar signal to the satellite are monitored in different time and changes of the line of sight (LOS) distances can detect ground surface movements. Natural reflectors are abundant in many places specially in urban areas. However, areas that are densely vegetated or covered by snow have limitations for InSAR technique and therefore artificial corner reflectors, passive or active ones, can be used instead. These corner reflectors are devices which provide precise measurement points and can be installed at desired locations. These devices can measure temporal LOS changes of the measurement point precisely using InSAR technique.

Since 2020, Lantmäteriet has installed three active electronic corner reflectors (ECR) and several types of passive reflectors (CR) in different locations of Sweden. 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 colocated permanent GNSS stations and corner reflectors can potentially contribute to the development and validation of the national and European ground motion services. Moreover, the colocation helps to map the relative ground motions estimated with InSAR to an absolute geodetic refercne frame. 

 

Keywords
InSAR, Corner reflector, Geodetic infrastructure, Ground motion
National Category
Earth and Related Environmental Sciences Remote Sensing
Identifiers
urn:nbn:se:hig:diva-38653 (URN)
Conference
EUREF 2022 SYMPOSIUM, 31 May - 3 June 2022, Zagreb, Croatia
Available from: 2022-05-30 Created: 2022-05-30 Last updated: 2022-05-31Bibliographically approved
Projects
Back to Fennoscandia Tectonics (FENETEC) using satellite geodesy correlated with analogue models [2008-03443_VR]; Uppsala UniversityBack to Fennoscandia Tectonics (FENETEC) using satellite geodesy correlated with analogue models [2008-07936_VR]; Uppsala University
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-1744-7004

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