| 1. |
- Agha Karimi, Armin, et al.
(författare)
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Multidecadal sea level variability in the Baltic sea and its impact on acceleration estimations
- 2021
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Ingår i: Frontiers in Marine Science. - : Frontiers. - 2296-7745. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- Multidecadal sea level variation in the Baltic Sea is investigated from 1900 to 2020 deploying satellite and in situ datasets. As a part of this investigation, nearly 30 years of satellite altimetry data are used to compare with tide gauge data in terms of linear trend. This, in turn, leads to validation of the regional uplift model developed for the Fennoscandia. The role of North Atlantic Oscillation (NAO) in multidecadal variations of the Baltic Sea is also analyzed. Although NAO impacts the Baltic Sea level on seasonal to decadal time scales according to previous studies, it is not a pronounced factor in the multidecadal variations. The acceleration in the sea level rise of the basin is reported as statistically insignificant in recent studies or even decelerating in an investigation of the early 1990s. It is shown that the reason for these results relates to the global warming hiatus in the 1950s−1970s, which can be seen in all eight tide gauges used for this study. To account for the slowdown period, the acceleration in the basin is investigated by fitting linear trends to time spans of six to seven decades, which include the hiatus. These results imply that the sea level rise is accelerated in the Baltic Sea during the period 1900–2020.
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| 2. |
- Alizadeh-Khameneh, Amin, et al.
(författare)
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A field method to estimate the uncertainty of RTK measurements
- 2023
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Ingår i: Survey review - Directorate of Overseas Surveys. - : Informa UK Limited. - 0039-6265 .- 1752-2706. ; , s. 1-8
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Tidskriftsartikel (refereegranskat)abstract
- The expected accuracies obtainable with Network Real-Time Kinematic (NRTK) measurements are of interest to surveyors working on construction projects. This study introduces an NRTK-based free stationing method called RUFRIS (Real Time Updated Free Station) which is independent from physically marked points. Integration of total station distance and direction observations with NRTK measurements enables uncertainty estimation of both total station and surveyed NRTK points. In Sweden, NRTK is conducted using the national network of permanent reference stations with different densifications (10, 35, 70 km). This paper investigates the applicability of the RUFRIS-method to estimate the uncertainty of NRTK measurements in the field.
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| 3. |
- Alizadeh Khameneh, Mohammad Amin, et al.
(författare)
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Investigation of the RUFRIS Method with GNSS and Total Station for Leveling
- 2017
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Konferensbidrag (refereegranskat)abstract
- The establishment of leveling benchmarks for performing geodetic measurements, for instance in construction works, is usually costly and laborious due to a mass of field works in transferring the height from nearby known benchmarks. In this study, a real-time updated free station (RUFRIS) method is investigated to be used as an alternative approach for the traditional leveling. The coordinates of a RUFRIS station are determined by establishing a total station on the point, and performing a free-station by observing some points with both Real-Time Kinematic (RTK) GNSS and total station distance and direction observations. The study is conducted based on data from the East Link project in Sweden, where a 150 km long high-speed railway is to be constructed. The results show a standard deviation of 7 mm between the RUFRIS and leveling heights in this project and imply the feasibility of replacing the traditional leveling methods with RUFRIS in projects with low accessibility to benchmarks.
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| 4. |
- Alizadeh Khameneh, Mohammad Amin, et al.
(författare)
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Optimal Vertical Placement of Total Station
- 2018
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Ingår i: Journal of Surveying Engineering. - 0733-9453 .- 1943-5428.
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Tidskriftsartikel (refereegranskat)abstract
- When using the free station method, a Total Station (TS) is established by performing distance and angle observations toward a number of Control Points (CPs). The quality of the establishment is crucial for the quality of subsequent measurements. The optimal horizontal location of the TS has been investigated in previous studies. Even the vertical precision is important in many applications, especially with significant height variations. Therefore in this paper, we focus on the optimality of vertical location of the TS. As an optimality criterion, the sum of TS coordinates and orientation variances is used. To investigate the optimization problem, an analytical as well as a trial and error method is developed. Both methods showed that the height component has no significant influence on the optimal vertical placement of the TS. Inspection of results from the trial and error method, where the CPs are moved in different height layers, indicates differences in the height uncertainty of the establishment in micrometer range, which is negligible for most engineering applications.
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| 5. |
- Andersson, Johan Vium, 1971-
(författare)
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A Complete Model for Displacement Monitoring Based on Undifferenced GPS Observations
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- During recent years there has been a great focus on the climate changes within the media. More or less every day more newspaper articles are presented about the global warming issue and the effect on us human race. Climate models predict higher temperatures and more rain in the northern part of Europe. It is also predicted that the weather will become more extreme e.g. it will rain a lot during longer periods than has been the norm. If these predictions are correct, the amount of water that is going to be transported away in streams and rivers will increase and so also will the subsoil water level. The latter increases the risk for landslides in areas with fine grained soils. An early warning system that is able to alert people before a landslide take place would be of great interest. The purpose of this work is to develop a complete real-time displacement monitoring system based on observations from several GPS-receivers that could be used as an early warning system. Due to the complex correlation structure of the traditionally used double differences, an alternative method based on undifferenced observations is used. Theoretically this approach shows some advantages and simplifies the correlative structure of observables compared to the double differenced method. A complete model for the undifferenced approach is presented in this thesis including its software implementation. A displacement detection system includes not only the positioning algorithms, but also methods to detect if any displacement occurs. There are many methods available to discriminate displacements, which are used in the traditional control of manufacturing processes. Several of these methods are compared in this thesis, such as the Shewhart chart, different Weighted Moving Average (WMA) charts and the CUmulative SUMmation (CUSUM). Practical tests show that it is possible to detect an abrupt shift on sub centimetre level at the same epoch as the shift occurs. Smaller shifts are also detectable with the applied approach but with a slightly longer detection time.
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| 6. |
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| 7. |
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| 8. |
- Bagherbandi, Mohammad, Professor, et al.
(författare)
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Physical and Geometric Effects on the Classical Geodetic Observations in Small-Scale Control Networks
- 2023
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Ingår i: Journal of Surveying Engineering. - : ASCE. - 0733-9453 .- 1943-5428. ; 149:1
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Tidskriftsartikel (refereegranskat)abstract
- In classical two-dimensional (2D) geodetic networks, reducing slope distances to horizontal ones is an important task for engineers. These horizontal distances along with horizontal directions are used in 2D geodetic adjustment. The common practice for this reduction is the use of vertical angles to reduce distances using trigonometric rules. However, one faces systematic effects when using vertical angles. These effects are mainly due to refraction, deflection of the vertical (DOV), and the geometric effect of the reference surface (sphere or ellipsoid). To mitigate refraction and DOV effects, one can choose to observe the vertical angles reciprocally if the baseline points’ elevation difference is small. This paper quantifies these effects and proposes a proper solution to eliminate the effects in small-scale geodetic networks (where the longest distances are less than 5 km). The goal is to calculate slope distances into horizontal ones appropriately. For this purpose, we used the SWEN17_RH2000 quasigeoid model (in Sweden) to study the impact of the DOV applying different baseline lengths, azimuths, and vertical angles. Finally, we propose an approach to study the impact of the geometric effect on vertical angles. We illustrate that the DOV and the geometric effects on vertical angles measured reciprocally are significant if the height difference of the start point and endpoint in the baseline is large. Geometric correction should be considered for the measured vertical angles to calculate horizontal distances correctly if the network points are not on the same elevation, even if the vertical angles are measured reciprocally.
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| 9. |
- Bagherbandi, Mohammad, Professor, et al.
(författare)
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Physical and Geometric Effects on the Classical Geodetic Observations in Small-Scale Control Networks
- 2023
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Ingår i: Journal of Surveying Engineering. - : American Society of Civil Engineers (ASCE). - 0733-9453 .- 1943-5428. ; 149:1
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Tidskriftsartikel (refereegranskat)abstract
- In classical two-dimensional (2D) geodetic networks, reducing slope distances to horizontal ones is an important task for engineers. These horizontal distances along with horizontal directions are used in 2D geodetic adjustment. The common practice for this reduction is the use of vertical angles to reduce distances using trigonometric rules. However, one faces systematic effects when using vertical angles. These effects are mainly due to refraction, deflection of the vertical (DOV), and the geometric effect of the reference surface (sphere or ellipsoid). To mitigate refraction and DOV effects, one can choose to observe the vertical angles reciprocally if the baseline points' elevation difference is small. This paper quantifies these effects and proposes a proper solution to eliminate the effects in small-scale geodetic networks (where the longest distances are less than 5 km). The goal is to calculate slope distances into horizontal ones appropriately. For this purpose, we used the SWEN17_RH2000 quasigeoid model (in Sweden) to study the impact of the DOV applying different baseline lengths, azimuths, and vertical angles. Finally, we propose an approach to study the impact of the geometric effect on vertical angles. We illustrate that the DOV and the geometric effects on vertical angles measured reciprocally are significant if the height difference of the start point and endpoint in the baseline is large. Geometric correction should be considered for the measured vertical angles to calculate horizontal distances correctly if the network points are not on the same elevation, even if the vertical angles are measured reciprocally.
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| 10. |
- Bagherbandi, Mohammad, Professor, et al.
(författare)
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Time transfer and significance of vertical land motion in relativistic geodesy applications: a review paper
- 2023
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Ingår i: Frontiers in Earth Science. - : Frontiers. - 2296-6463. ; 11
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Forskningsöversikt (refereegranskat)abstract
- Determination of the Earth’s gravity field and geopotential value is one of the fundamental topics in physical geodesy. Traditional terrestrial gravity and precise leveling measurements can be used to determine the geopotential values at a local or regional scale. However, recent developments in optical atomic clocks have not only rapidly improved fundamental science but also contributed to applied research. The latest generation of optical clocks is approaching the accuracy level of 10−18 when facilitating atomic clock networks. These systems allow examining fundamental theories and many research applications, such as atomic clocks applications in relativistic geodesy, to precisely determine the Earth’s gravity field parameters (e.g., geopotential values). According to the theory of relativistic geodesy, the frequency difference measured by an optical clock network is related to the gravity potential anomaly, provided that the effects of disturbing signals (i.e., tidal and non-tidal contributions) are filtered out. The relativistic geodesy principle could be used for a practical realization of global geodetic infrastructure, most importantly, a vertical datum unification or realization of height systems. This paper aims to review the background of relativistic (clock-based) geodesy and study the variations of optical atomic clock measurements (e.g., due to hydrology loading and land motion).
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