| 1. |
- Angenendt, Knut, 1982, et al.
(författare)
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Ionic liquid structures from large DFT calculations using mindless configurations
- 2010
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 114:48, s. 20577-20582
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Tidskriftsartikel (refereegranskat)abstract
- Three different popular imidazolium based ionic liquids (ILs); EMI-BF4, EMI-PF6, and EMI-TFSI, have been modeled by DFT calculations (B3LYP/6-311+G*) using large, up to 130 atom cluster models, for a better understanding of the structure and ion ion interactions in these ILs and ILs in general. Particular emphasis has been put on the role of appropriate starting structures and how the present large models differ from the ion-pair models of ILs generally used. The system size normalized ion ion interaction energies are shown to converge rapidly, and conformational equilibria and higher order properties like IR spectra are shown to be valuable as quality criteria. The explicit inclusion of an IL environment by the large cluster approach is also compared to using an implicit, continuum, strategy via SCRF C-PCM calculations.
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| 2. |
- Bengtsson, Lars, 1963
(författare)
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Electrical Measurement Systems and Methods
- 2014
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Bok (övrigt vetenskapligt/konstnärligt)abstract
- This book treats a wide range of aspects on electrical measurement systems and the methods used to acquire data from electronic systems. That includes sensors and sensor design, amplifiers such as differential and charge amplifiers, ADCs and DACs, digital oscilloscopes, cable theory and probes, noise and noise coupling, common and normal mode signals. This first part (chapters 1-8) doesn’t require any advanced mathematics and is aimed towards undergraduates. The second part (chapters 9-17) is on an advanced level (master level) and treats transform theory (Fourier, Laplace, z) and how to handle signals in frequency space. We cover the sampling theorem (Nyquist), resolution bandwidth, frequency spectrum distortions like aliasing and leakage and how to apply windows in a frequency spectrum. We also cover systems and signal processing in time-space, including convolution and correlation, filter theory and filter design (both analog and digital). The last chapters concern the statistical aspects on measurement systems and signals, like point and interval estimations, curve fitting and uncertainty estimations according to the GUM method.
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| 3. |
- Cherednichenko, Serguei, 1970, et al.
(författare)
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Online Detection of H2O and CO in the Humid Raw Gas from the Gasifier Using Terahertz Spectroscopy
- 2013
-
Ingår i: ICPS, 13 International Conference on Polygeneration Strategies, Sept.5-13, Vienna, Austria. - 9783950275483 ; , s. 51-58
-
Konferensbidrag (refereegranskat)abstract
- The integration of a gasifier with a complex multistage synthesis process, such as SNG synthesis, demands a fast monitoring of the gasifier performance. However, despite the availability of standard analyzers for determination of dry gas composition, there are still many practical difficulties remaining in the online measurement of tar and steam in the raw gas. For the detection of steam concentration, electromagnetic waves at terahertz frequencies (102-104 GHz) are promising with regard to development of a robust online measurement device for industrial application. The main reason for the high potential is the low risk for interference with the wide range of other molecules and that the transmission of electromagnetic waves at THz frequencies is rather low sensitive to deposits and particulate matter in the course of the beam compared to the conventional and well established wavelengths like infrared. In the present work, a THz gas spectrometer was designed and constructed to check the feasibility of applying this measurement technique at industrial scale. For this purpose, continuous flows of raw gas with various water and CO contents from the Chalmers gasifier as well as a flue gas with known water content from the biomass combustor were introduced to the spectrometer set-up. H2O and CO compositions in each stream were determined in an online manner. The results confirmed the possibility of applying strong rotational water lines at 448 and 380 GHz to develop reliable devices for online measurement of water vapor with excellent error interval. However, some difficulties were encountered for simultaneous detection CO concentration with water within the frequency range studied in this work (300-500 GHz).
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| 4. |
- Cherednichenko, Serguei, 1970, et al.
(författare)
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Terahertz Gas Spectrometer
- 2014
-
Ingår i: Swedish Microwave Days March 11-12, 2014, Gothenburg, Sweden.
-
Konferensbidrag (refereegranskat)abstract
- We present a 300-500GHz gas spectrometer built for and practically tested at the 2–4-MW indirect gasifier at the Chalmers Power Center. The primary goal is precise online measurements of H2O vapor and CO concentrations in the producer gas. Experimentally obtained H2O vapor concentration resolution was about 1% at the conditions of 50% VMR and 400 deg.C.
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| 5. |
- Chernikova, Dina, 1982, et al.
(författare)
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Development of the Neutron-Gamma-Neutron (NGN) approach for the fresh and spent fuel assay
- 2012
-
Ingår i: Proceedings of The 53nd Annual Meeting of the Institute of Nuclear Materials Management.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In connection with current safety and complexity limitations for installations which usekeV neutrons for irradiation in the fresh and spent fuel assay, in medicine, geophysicaland detection fields, there is a long felt need of effective, light, inexpensive systems withlonger lifetimes and the possibility to ”switch off” the source during transportation andwork break. The present paper discusses an opportunity of creating a novel technique basedon using a pulsed neutron generator, hydrogen moderator and beryllium, which will enablecreation of a compact and inexpensive facility capable to satisfy all requirements. The mainidea of the proposed method consists in using photonuclear reaction in beryllium due togamma irradiation originating from (n,gamma) reaction in a hydrogen containing moderator.After the neutron pulse of a modern compact DD neutron generator in hydrogen-containingmoderator, high-energy neutrons (approximately 2.5 MeV) get slowed down mainly by elasticscattering to near thermal energies. At thermal energies, the neutrons diffuse through thematerial until they undergo thermal capture (capture is dominated by hydrogen neutronabsorbers). When a hydrogen atom captures a thermal neutron, it turns into deuteriumwith the release of a large component of 2.23 MeV gamma-rays. Beryllium is one of thefew elements in nature that undergoes a photonuclear reaction with this gamma energyrange (e.g. deuterium has a low energy 2.225 MeV photonuclear threshold). Thus, as theberyllium has lower neutron-binding energy, 1.667 MeV (photonuclear reaction threshold),a photonuclear reaction will take place with emission of neutrons with energy defined by thekinematic equation. Thus, this method allows to obtain a high quality epithermal neutronbeam without using a complex system with particle accelerator or radioisotope sources withlimited decay time. The proposed method has been studied using Monte Carlo simulations,which made it possible to define the theoretical limits of the use of the NGN approach inindustrial applications. The paper will presents the results of these investigations.
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| 6. |
- Chernikova, Dina, 1982, et al.
(författare)
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Testing a direct method for evaluating the concentration of boron in a fuel pool using scintillation detectors, and a 252Cf and an 241Am-Be source
- 2013
-
Ingår i: Proceeding of ESARDA meeting 2013.
-
Konferensbidrag (refereegranskat)abstract
- The present investigations are aimed at the development and testing of a direct non-destructive method for evaluating the concentration of boron in a fuel pool using scintillation detectors. The method uses a modified ratio between two gamma lines with energy of 480 keV and 2.23 MeV. These lines belong to the capture of a thermal neutron in boron and hydrogen, respectively. The relation between them can reveal the concentration of boron in the fuel pond.The method proposed was tested in a laboratory experiment with a 252Cf and an 241Am-Be source. EJ-309 liquid scintillation detectors were used for measurements of gamma spectra. The concentration of boron in water varied from 1550 ppm to 4200 ppm. The optimization and test studies were performed via MCNPX simulations.The results of these tests are provided in the present paper and they show that the boron content in water can be determined through using the characteristics of gamma lines with energy of 480 keV and 2.23 MeV.
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| 7. |
- Dufek, Jan, 1978
(författare)
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Building the nodal nuclear data dependences in a many-dimensional state-variable space
- 2011
-
Ingår i: Annals of Nuclear Energy. - : Elsevier BV. - 0306-4549 .- 1873-2100. ; 38:7, s. 1569-1577
-
Tidskriftsartikel (refereegranskat)abstract
- We present new methods for building the polynomial-regression based nodal nuclear data models. Thedata models can reflect dependences on a large number of state variables, and they can consider varioushistory effects. Suitable multivariate polynomials that approximate the nodal data dependences are identifiedefficiently in an iterative manner. The history effects are analysed using a new sampling scheme forlattice calculations where the traditional base burnup and branch calculations are replaced by a largenumber of diverse burnup histories. The total number of lattice calculations is controlled so that the datamodels are built to a required accuracy.
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| 8. |
- Dufek, Jan, 1978-
(författare)
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Complex models of nodal nuclear data
- 2011
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Ingår i: International Conference on Mathematics and Computational Methods Applied to Nuclear Science and Engineering (M&C 2011). - 9788563688002
-
Konferensbidrag (refereegranskat)abstract
- During the core simulations, nuclear data are required at various nodal thermal-hydraulic and fuel burnup conditions. The nodal data are also partially affected by thermal-hydraulic and fuel burnup conditions in surrounding nodes as these change the neutron energy spectrum in the node. Therefore, the nodal data are functions of many parameters (state variables), and the more state variables are considered by the nodal data models the more accurate and flexible the models get. The existing table and polynomial regressionmodels, however, cannot reflect the data dependences on many state variables. As for the table models, the number of mesh points (and necessary lattice calculations) grows exponentially with the number of variables. As for the polynomial regression models, the number of possible multivariate polynomials exceeds the limits of existing selection algorithms that should identify a few dozens of the most important polynomials. Also, the standard scheme of lattice calculations is not convenient for modelling the data dependences on various burnup conditions since it performs only a single or few burnup calculations at fixed nominal conditions. We suggest a new efficient algorithm for selecting the most important multivariate polynomials for the polynomial regression models so that dependences on many state variables can be considered. We also present a new scheme for lattice calculations where a large number of burnup histories are accomplished at varied nodal conditions. The number of lattice calculations being performed and the number of polynomials being analysed are controlled and minimised while building the nodal data models of a required accuracy.
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| 9. |
- Frennert, Susanne, PhD, et al.
(författare)
-
Using attention cards to facilitate active participation in eliciting old adults' requirements for assistive robots
- 2013
-
Ingår i: IEEE International Workshop on Robot and Human Interactive Communication. - : IEEE conference proceedings. - 9781479905072 ; , s. 774-779, s. 774-779
-
Konferensbidrag (refereegranskat)abstract
- Engaging old users in the exploration of future product concepts can be challenging. It is of great value to find ways to actively involve them in the design of novel technologies intended for them, particularly when they have no prior experience of the technology in question. One obstacle in this process is that many old people do not identify themselves as being old or they think that it (the technology) would be good for others but not themselves. This paper presents a card method to overcome this obstacle. A full-day workshop with three internal focus groups was run with 14 participants. Based on our experience, we propose a way in which active participation in the process of eliciting user requirements for assistive robots from old users with no prior experience of assistive robots can be carried out.
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| 10. |
- Gremyr, Ida, 1975, et al.
(författare)
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A developmental view on implementation of quality management concepts
- 2014
-
Ingår i: International Journal of Quality and Service Sciences. - : Emerald Group Publishing Limited. - 1756-669X .- 1756-6703. ; 6:2/3, s. 143-154
-
Tidskriftsartikel (refereegranskat)abstract
- Purpose – The purpose of this paper is to examine the value of a developmental learning view on implementation of quality management (QM) concepts. QM concepts are common in various organizations; some implement them smoothly, others struggle and sometimes even abandon the initiatives. What is then a successful implementation – is it the use a specific QM method as a standard problem solving approach, or is it that learning has occurred during implementation?Design/methodology/approach – The paper is based on an illustrative case study carried out at a hospital in western Sweden. The data have been collected through about 130 hours of participation in project work by the first author and through seven face-to-face interviews of about one hour each.Findings – It is shown that a Design for Six Sigma pilot project with a narrow view on implementation could be regarded as a failure, but it gave rise to much learning and new improved ways of working. Hence, it is argued that a developmental view on implementation can support learning by an emergent and experimental approach to implementation processes.Originality/value – Much research has been done on how to increase the success rate of implementations of QM initiatives, e.g. procedures to follow to reach an outcome where the new way of working is standard procedure. Less research has problematized the implementation process, questioning what a successful outcome of an implementation is.
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| 11. |
- Huang, L., et al.
(författare)
-
Anomalous temperature dependence of elastic constant c(44) in V, Nb, Ta, Pd, and Pt
- 2010
-
Ingår i: Journal of Physics and Chemistry of Solids. - : Elsevier BV. - 0022-3697 .- 1879-2553. ; 71:8, s. 1065-1068
-
Tidskriftsartikel (refereegranskat)abstract
- The anomalous temperature dependence of elastic constant c(44) for elements V. Nb, Ta, Pd, and Pt, has been calculated using first-principles theory. It is shown that the variation of elastic constant for simple elements can be approximated as the sum of thermal expansion and electronic components. The thermal expansion contributes the normal linearly decreasing effect to the elastic constant with temperature, while electronic contribution is determined by the unique character of electronic structure of elements and leads to the anomalous effect to the elastic constant with temperature.
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| 12. |
- Insulander Björk, Klara L, 1982
(författare)
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Thorium-plutonium fuel for long operating cycles in PWRs - preliminary calculations
- 2012
-
Ingår i: Proceedings of the Thorium and Rare Earths Conference.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Preliminary calculations have been carried out to investigate the possibility of extending oper-ating cycle length in PWRs by use of Thorium-Plutonium mixed oxide fuel (Th-MOX). Thecalculations have been carried out in two dimensions, using the fuel assembly burnup simula-tion program CASMO-5. The reload scheme and the operating parameters are modelled on theSwedish PWR Ringhals 3 and a normal UOX fuel assembly designed for this reactor has beenused as a reference. Results show that an extension of the currently employed 12-month oper-ating cycle length is possible, either with a burnable absorber or with a modified fuel assemblydesign, assuming the same 3-batch reload scheme as currently used in Ringhals 3.The initial k∞ of the new Th-MOX fuel design was designed not to exceed that of the refer-ence UOX fuel. The power peaking factor is initially significantly lower than the reference,but slightly higher later in the life of the fuel assembly. All reactivity coefficients are withinacceptable range. The worth of control rods and soluble boron are lower than the reference, asexpected for a plutonium-bearing fuel.
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| 13. |
- Jagtap, Santosh, et al.
(författare)
-
Design for the BOP and TOP markets: Strategies used by the design students
- 2013
-
Konferensbidrag (refereegranskat)abstract
- The base (BOP) and the top (TOP) of the world income pyramid represent the poor people and the people from developed countries, respectively. About two-fifths of the world population can be categorized as poor. Poverty is a trap because children born to poor parents are likely to grow up to be poor adults. In recent years, a poverty reduction approach that combines business development with poverty alleviation has received attention. The design of products for the BOP is an important ingredient of this poverty reduction approach. While companies are beginning to address the product needs of the BOP, there is limited practical and theoretical knowledge to support them. The current understanding of the design for the BOP is limited. This study aims at exploring the differences between the design strategies used by the industrial design students in designing products for the BOP and TOP markets. The results indicate the differences between their design strategies (i.e. problem driven strategy, solution driven strategy) in designing products for the BOP and TOP markets. We have discussed the implications of the findings for design practice and education. In particular, we have discussed how university-based design projects for the BOP can help in developing students’ different design skills.
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| 14. |
- Jagtap, Santosh, et al.
(författare)
-
Ideation Metrics: Interdependency between Average Novelty and Variety
- 2012
-
Ingår i: DS 70: Proceedings of DESIGN 2012, the 12th International Design Conference, Dubrovnik, Croatia. - 1847-9073. - 9789537738174 ; , s. 1881-1892, s. 1881-1892
-
Konferensbidrag (refereegranskat)abstract
- Abstract in Undetermined The importance of ideation in the conceptual design phase has been widely accepted. Shah et al. (2003) developed four key metrics for evaluating a designer’s exploration and expansion of design space. The four metrics are: novelty, variety, quality, and quantity of designs. The mean of novelty scores of ideas in a set (i.e. Average Novelty - AN) has also been used in some ideation studies. However, many of the studies that have computed AN and variety, have not examined the interdependency between them. This research aims at examining the interdependency between AN and variety.
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| 15. |
- Jahanmiri, Mohsen, 1953
(författare)
-
Particle Image Velocimetry: Fundamentals and Its Applications
- 2011
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Particle image velocimetry (PIV) is the newest entrant to the field of fluid flow measurement and provides instantaneous velocity fields over global domains. As the name suggests, PIV records the position over time of small tracer particles introduced into the flow to extract the local fluid velocity. Thus, PIV represents a quantitative extension of the qualitative flow visualization techniques that have been practised for several decades. This paper gives a brief background on evolution of PIV and then its principle of operation, main features and basic elements are explaind. Errors in PIV occurring while measurements are discussed and, the state-of-the-art of the technique today is overviewed and illustrated by reference to recent, seminal publications describing both the development and application of PIV.
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| 16. |
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| 17. |
- Larson, Kristine, et al.
(författare)
-
Coastal Sea Level Measurements Using a Single Geodetic GPS Receiver
- 2013
-
Ingår i: Advances in Space Research. - : Elsevier BV. - 1879-1948 .- 0273-1177. ; 51:8, s. 1301-1310
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents a method to derive local sea level variations using data from a single geodetic-quality Global Navigation Satellite System (GNSS) receiver using GPS (Global Positioning System) signals. This method is based on multipath theory for specular reflections and the use of Signal-to-Noise Ratio (SNR) data. The technique could be valuable for altimeter calibration and validation. Data from two test sites, a dedicated GPS tide gauge at the Onsala Space Observatory (OSO) in Sweden and the Friday Harbor GPS site of the EarthScope Plate Boundary Observatory (PBO) in USA, are analyzed. The sea level results are compared to independently observed sea level data from nearby and in situ tide gauges. For OSO, the Root-Mean-Square (RMS) agreement is better than 5 cm, while it is on the order of 10 cm for Friday Harbor. The correlation coefficients are better than 0.97 for both sites. For OSO, the SNR-based results are also compared with results from a geodetic analysis of GPS data of a two receivers/antennae tide gauge installation. The SNR-based analysis results in a slightly worse RMS agreement with respect to the independent tide gauge data than the geodetic analysis (4.8 cm and 4.0 cm, respectively). However, it provides results even for rough sea surface conditions when the two receivers/antennae installation no longer records the necessary data for a geodetic analysis.
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| 18. |
- Larson, Kristine, et al.
(författare)
-
The GPS Tide Gauge Problem Revisited
- 2011
-
Ingår i: American Geophysical Union Fall Meeting 2011, 5-9 December, San Francisco, USA.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- It is well-known that GPS instruments can be used to measure local sea level. In most experiments, two antennas are deployed at a coastal site. A geodetic antenna - optimized for RHCP signals - is used in the traditional orientation and tracks the direct signal. The second antenna is optimized for reflected signals - which are primarily LHCP - and is pointed towards the ocean. The sea surface can then be estimated by analyzing the carrier phase data. While the data from the "up" antenna are dominated by the direct signal, the effects of signals reflected from the ocean are also present in its data. Thus in principle, one might be able to estimate sea level using only data from the "up" antenna. This is similar in concept to recent multipath studies where geodetic GPS installations are being used to measure soil moisture variations and snow depth.We have analyzed GPS data for a three-month period from a GPS tide gauge installation at the Onsala Space Observatory. It is located on the western coast of Sweden. We used the SNR data from the "up" antenna only. The data were windowed by azimuth for ocean-reflections and elevation angles from 18-40 degrees. This provides hourly sea level measurements. Comparisons were made to an average for tide gauge records 18 km south and 33 km north of Onsala. The standard deviation of the residual between our solutions and the tide gauges is 4.9 cm. This is less precise than the combined up-down antenna system of 2.6 cm. These precision values include errors associated with real tidal motion at the GPS site. While the "down" antenna performs poorly in high-wind conditions (> 8 m/s), we found that the "up" antenna performs significantly better at these times.
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| 19. |
- Larsson, Gustav, et al.
(författare)
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A case study of municipal solid waste in Nepal compared to the situation in the European Union and Sweden
- 2010
-
Ingår i: Proceedings Linnaeus ECO-TECH´10, Kalmar, Sweden, Nov 22-24, 2010. ; , s. 429-438
-
Konferensbidrag (refereegranskat)abstract
- Nepal, situated in the Himalayan belt has a rapidly growing population together with highurbanisation rate. These factors are currently causing problems connected to municipal solidwaste (MSW). E.g. leakage of hazardous substances to soil and surrounding aquatic systems,spread of odour and naturally unfamiliar materials to natural biotopes, all of which generateenvironmental damage and health problems. There are certain differences in waste generationand waste composition between urban areas of Nepal. In order to retrieve a broad picture ofthe current waste management situation, three population differentiated municipalities indifferent areas of the country were investigated. Studies of the MSW regarding compositionand generation were conducted. Moreover, waste management in Nepal was compared withthe basic waste management in the European Union (EU) and Sweden. Landfill sites (LFS) inGhorahi Municipality, Pokhara Sub-metropolitan City and Kathmandu Metropolitan Citywere studied. Our studies show differences in waste composition, generation and managementbetween the three locations. The differences are somewhat interconnected with populationsize and tourism. Cities with higher population and more tourism tend to have a highergeneration and more diverse MSW. Nevertheless, the urban areas of Nepal are very much inneed of a more structured waste management system, a system more alike the wastemanagement of EU. Apart from structural problems, there are attitude and behavioural issuesthat needs to be dealt with. Further studies regarding social patterns, attitude and behaviour,as well as the economic flow of MSW, needs to be conducted in order to retrieve an evenbroader picture and understand important underlying issues.
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| 20. |
- Laukkanen, P., et al.
(författare)
-
Core-level shifts of the c(8 x 2)-reconstructed InAs(100) and InSb(100) surfaces
- 2010
-
Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 177:1, s. 52-57
-
Tidskriftsartikel (refereegranskat)abstract
- We have studied In-stabilized c(8 2)-reconstructed InAs(1 0 0) and InSb(1 0 0) semiconductor surfaces, which play a key role in growing improved III-V interfaces for electronics devices, by core-level photoelectron spectroscopy and first-principles calculations. The calculated surface core-level shifts (SCLSs) for the zeta and zeta a models, which have been previously established to describe the atomic structures of the III-V(1 00)c(8 x 2) surfaces, yield hitherto not reported interpretation for the As 3d, In 4d, and Sb 4d core-level spectra of the III-V(1 00)c(8 x 2) surfaces, concerning the number and origins of SCLSs. The fitting analysis of the measured spectra with the calculated zeta and zeta a SCLS values shows that the InSb spectra are reproduced by the zeta SCLSs better than by the zeta a SCLSs. Interestingly, the zeta a fits agree better with the InAs spectra than the zeta fits do, indicating that the zeta a model describes the InAs surface better than the InSb surface. These results are in agreement with previous X-ray diffraction data. Furthermore, an introduction of the complete-screening model, which includes both the initial and final state effects, does not improve the fitting of the InSb spectra, proposing the suitability of the initial-state model for the SCLSs of the III-V(1 0 0)c(8 x 2) surfaces. The found SCLSs are discussed with the ab initio on-site charges.
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| 21. |
- Lee, Kyuho, et al.
(författare)
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Benchmarking van der Waals density functionals with experimental data: potential-energy curves for H2 molecules on Cu(111), (100) and (110) surfaces
- 2012
-
Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 24:42
-
Tidskriftsartikel (refereegranskat)abstract
- Detailed physisorption data from experiment for the H2 molecule on low-index Cu surfaces challenge theory. Recently, density functional theory (DFT) has been developed to account for nonlocal correlation effects, including van der Waals (dispersion) forces. We show that the functional vdW-DF2 gives a potential-energy curve, potential-well energy levels and difference in lateral corrugation promisingly close to the results obtained by resonant elastic backscattering–diffraction experiments. The backscattering barrier is sensitive to the choice of exchange functional approximation. Further, the DFT-D3 and TS-vdW corrections to traditional DFT formulations are also benchmarked, and deviations are analyzed.
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| 22. |
- Löfgren, Johan, 1983, et al.
(författare)
-
High-rate local sea level monitoring with a GNSS-based tide gauge
- 2010
-
Ingår i: Proceedings of the 2010 IEEE International Geoscience and Remote Sensing Symposium, Proceedings DVD-ROM. - 9781424495665 ; , s. 3616-3619
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We present first results from the analysis of high-rate observations with a GNSS-based tide gauge at the Onsala Space Observatory. The goal is to determine local sea level with high temporal resolution. The GNSS-based tide gauge makes use of right-hand circular polarized GNSS signals that are directly received and left-hand circular polarized GNSS signals that are reflected from the sea surface. An experimental setup of the GNSS-based tide gauge was operated in the spring of 2010 and data were recorded with a sampling rate of 20 Hz.We analyzed data decimated to 1 Hz using different temporal resolution between 5 and 240 seconds, and the resulting time series of local sea level were compared to each other and to results from two stilling well gauges. The comparison with the data from the stilling well gauges shows a common trend.The comparison of the results from analyses with different temporal resolution show consistent results. There is also an indication that the GNSS-based tide gauge might be able to give information on the sea surface state.
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| 23. |
- Löfgren, Johan, 1983, et al.
(författare)
-
Monitoring coastal sea level using reflected GNSS signals
- 2011
-
Ingår i: Advances in Space Research. - : Elsevier BV. - 1879-1948 .- 0273-1177. ; 47:2, s. 213-220
-
Tidskriftsartikel (refereegranskat)abstract
- A continuous monitoring of coastal sea level changes is important for human society since it is predicted that up to 332 million people in coastal and low-lying areas will be directly affected by flooding from sea level rise by the end of the 21st century. The traditional way to observe sea level is using tide gauges that give measurements relative to the Earth’s crust. However, in order to improve the understanding of the sea level change processes it is necessary to separate the measurements into land surface height changes and sea surface height changes. These measurements should then be relative to a global reference frame. This can be done with satellite techniques, and thus a GNSS-based tide gauge is proposed. The GNSS-based tide gauge makes use of both GNSS signals that are directly received and GNSS signals that are reflected from the sea surface. An experimental installation at the Onsala Space Observatory (OSO) shows that the reflected GNSS signals have only about 3 dB less signal-to-noise-ratio than the directly received GNSS signals. Furthermore, a comparison of local sea level observations from the GNSS-based tide gauge with two stilling well gauges, located approximately 18 km and 33 km away from OSO, gives a pairwise root-mean-square agreement on the order of 4 cm. This indicates that the GNSS-based tide gauge gives valuable results for sea level monitoring.
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| 24. |
- Löfgren, Johan, 1983
(författare)
-
Observing Sea Level Using Reflected Global Navigation Satellite System Signals
- 2011
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Sea-level rise due to global warming is predicted to have a large impact on human society, especially for populations living in coastal regions and on islands. It is therefore of great importance to monitor the sea level and to increase the understanding of the local hydrodynamic and meteorological responses to a global sea-level rise.Presented in this thesis is a technique to measure local sea level using Global Navigation Satellite System (GNSS) signals. This GNSS-based tide gauge acquires both the directly received GNSS signals and the GNSS signals that are reflected off the sea surface, using standard geodetic GNSS receivers. With the directly received signals the installation measures land-surface height changes, whereas the reflected signals are used to measure sea-surface height changes. Both measurements are done with respect to the Earth's centre of mass. By combining these observations it is possible to estimate the local sea level, which is directly related to the volume of the ocean.Several GNSS-based tide gauge campaigns have been carried out at the Onsala Space Observatory (OSO) on the west coast of Sweden. Today the installation is still in place and continues to record GNSS data with a sampling frequency of 1 Hz. In this thesis, data from the campaigns are analysed in a post-processing mode with an in-house developed software. Sea-level estimates are produced with a temporal resolution from 5 s to 20 min and compared to independent sea-level observations from stilling well gauges located approximately 18 km south and 33 km north of OSO. The results for three months of GNSS-derived sea level show an agreement, with respect to the stilling well gauge sea level, with typical root-mean-square differences of better than 6 cm and correlation coefficients of higher than 0.95.Additionally, using an ocean-tide analysis of three months of sea-level observations from the GNSS-based tide gauge, it was possible to determine several tidal components, i.e., M2, S2, N2, O2, and M4. The amplitudes and phases show reasonable agreement with the ones derived from one year of stilling well gauge sea-level data.
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| 25. |
- Löfgren, Johan, 1983, et al.
(författare)
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Remote Sensing of the Coastal Ocean with Standard Geodetic GNSS-Equipment
- 2012
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Ingår i: European Geosciences Union General Assembly 2012, 22-27 April, Vienna, Austria.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We use standard geodetic Global Navigation Satellite System (GNSS) equipment to perform remote sensing measurements of the coastal ocean. This is done by a so-called GNSS-based tide gauge that uses both direct GNSS-signals and GNSS-signals that are reflected off the sea surface. Our installation is located at the Onsala Space Observatory (OSO) at the west coast of Sweden and consists of a zenith-looking Right Hand Circularly Polarized (RHCP) and a nadir-looking Left Hand Circularly Polarized (LHCP) antenna. Each antenna is connected to a standard geodetic-type GNSS-receiver.We applied two different analysis strategies to our GNSS data set. The first strategy is based on a traditional geodetic differential analysis [Löfgren et al., 2011] and makes use of the data from both receivers; connected to the zenith and the nadir looking antennae. This approach results in local sea level that is automatically corrected for land motion, meaning that the GNSS-based tide gauge can provide reliable sea-level estimates even in tectonic active regions. The second strategy focuses on the Signal-to-Noise Ratio (SNR) recorded with the receiver connected to the zenith-looking antenna [Larson et al., 2011]. The SNR is affected by multipath originating from the sea surface reflections. Analysis of the SNR data allows to determine the distance between the antenna and the reflecting surface, and thus to measure sea surface height. Results from both analysis strategies are compared to independently observed sea-level data from two stilling-well gauges operated by the Swedish Meteorological and Hydrological Institute (SMHI), which lie in a distance of several km from OSO. The root-mean-square agreement between the different time series of several month's length is on the order of 5 cm and better. These results indicate the large potential for using coastal GNSS-sites for the monitoring of the coastal ocean.References:Löfgren J.S., Haas R., Scherneck H-G., Bos M.S., (2011), Three months of local sea level derived from reflected GNSS signals, Radio Science, 46 (RS0C05).Larson K., Löfgren J.S., Haas R., (2011), The GPS tide gauge problem revisited, AGU Fall Meeting, 5-9 December, San Francisco, USA, Poster.
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