| 1. |
- Fenty, Ian, et al.
(författare)
-
Oceans Melting Greenland : Early Results from NASA’s Ocean-Ice Mission in Greenland
- 2016
-
Ingår i: Oceanography. - : The Oceanography Society. - 1042-8275. ; 29:4, s. 72-83
-
Tidskriftsartikel (refereegranskat)abstract
- Melting of the Greenland Ice Sheet represents a major uncertainty in projecting future rates of global sea level rise. Much of this uncertainty is related to a lack of knowledge about subsurface ocean hydrographic properties, particularly heat content, how these properties are modified across the continental shelf, and about the extent to which the ocean interacts with glaciers. Early results from NASA's five-year Oceans Melting Greenland (OMG) mission, based on extensive hydrographic and bathymetric surveys, suggest that many glaciers terminate in deep water and are hence vulnerable to increased melting due to ocean-ice interaction. OMG will track ocean conditions and ice loss at glaciers around Greenland through the year 2020, providing critical information about ocean-driven Greenland ice mass loss in a warming climate.
|
|
| 2. |
- Forsberg, Fredrik, et al.
(författare)
-
3D micro-scale deformations of wood in bending : synchrotron radiation μCT data analyzed with digital volume correlation
- 2008
-
Ingår i: Journal of Structural Biology. - : Elsevier BV. - 1047-8477 .- 1095-8657. ; 164:3, s. 255-262
-
Tidskriftsartikel (refereegranskat)abstract
- A micro-scale three-point-bending experiment with a wood specimen was carried out and monitored by synchrotron radiation micro-computed tomography. The full three-dimensional wood structure of the 1.57 × 3.42 × 0.75 mm3 specimen was reconstructed at cellular level in different loading states. Furthermore, the full three-dimensional deformation field of the loaded wood specimen was determined by digital volume correlation, applied to the reconstructed data at successive loading states. Results from two selected regions within the wood specimen are presented as continuous displacement and strain fields in both 2D and 3D. The applied combination of synchrotron radiation micro-computed tomography and digital volume correlation for the deformation analysis of wood under bending stress is a novel application in wood material science. The method offers the potential for the simultaneous observation of structural changes and quantified deformations during in situ micro-mechanical experiments. Moreover, the high spatial resolution allows studying the influence of anatomical features on the fracture behaviour of wood. Possible applications of this method range from bio-mechanical observations in fresh plant tissue to fracture mechanics aspects in structural timber.
|
|
| 3. |
- Forsberg, Fredrik, et al.
(författare)
-
Full three-dimensional strain measurements on wood exposed to three-point-bending : analysis by use of digital volume correlation applied to synchrotron radiation micro-computed tomography image data
- 2010
-
Ingår i: Strain. - : Wiley. - 0039-2103 .- 1475-1305. ; 46:1, s. 47-60
-
Tidskriftsartikel (refereegranskat)abstract
- A microscale three-point bend experiment on wood has been carried out. The full 3D strain field of the microscale wood structure has been determined by use of digital volume correlation, based on reconstructed 3D image data acquired with synchrotron radiation micro-computed tomography. The wood specimen, which measures 1.57 × 3.42 × 0.75 mm3, was scanned in different load states along the three-point bend load cycle, from unloaded state to failure. The correlation algorithm is based on a Chebyshev polynomial description of the displacements, which allows a continuous representation of the 3D deformation fields. The methodology of the correlation algorithm is described thoroughly and its performance is tested for a 3D structure that is exposed to a virtual pre-defined deformation. The performance is tested both for noise free volume data as well as for structures with additive noise content. The performance test shows that the correlation algorithm resolves the applied deformation satisfyingly well. In the real experiment, on wood microstructure, the displacement fields show a structural behaviour that is consistent with what is expected for a specimen exposed to three-point bend. However, there are also anomalous effects present in the displacement fields that can be coupled to characteristic features in the cellular structure of the wood. Furthermore, 3D strain calculations based on the obtained displacement data shows a concentration of tensile strain in the region where the specimen eventually collapses. The experimental results show that the use of X-ray-based tomography with high spatial resolution in combination with digital volume correlation can successfully be used to perform 3D strain measurements on wood, at the microscale
|
|
| 4. |
|
|
| 5. |
- Matzka, Jürgen, et al.
(författare)
-
A new aeromagnetic survey of the North Pole and the Arctic Ocean north of Greenland and Ellesmere Island
- 2010
-
Ingår i: Earth Planets and Space. - : Society of Geomagnetism and Earth, Planetary and Space Sciences. - 1343-8832 .- 1880-5981. ; 62:10, s. 829-832
-
Tidskriftsartikel (refereegranskat)abstract
- We present a preliminary analysis of more than 50,000 km of aeromagnetic survey lines flown in the Arctic Ocean, acquired in 2009 with an optically pumped scalar magnetometer as part of the airborne geophysical survey 'LOMGRAV'. From the observations we removed main and magnetospheric fields as given by the CHAOS-3 field model (Olsen et al., 2010) and remaining external fields as monitored by the Canadian magnetic observatory Alert. The reduced data were levelled based on cross-over differences at line intersections. Finally, a grid was computed, upward continued by 3500 m and compared with the EMAG2 grid (Maus et al., 2009), showing a good general agreement but also areas with systematic differences. The obtained data are expected to be part of the next version of the World Digital Magnetic Anomaly Map (WDMAM).
|
|
| 6. |
- Mooser, René, et al.
(författare)
-
Estimation of affine transformations directly from tomographic projections in two and three dimensions
- 2013
-
Ingår i: Machine Vision and Applications. - : Springer Science and Business Media LLC. - 0932-8092 .- 1432-1769. ; 24:2, s. 419-434
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents a new approach to estimate two- and three-dimensional affine transformations from tomographic projections. Instead of estimating the deformation from the reconstructed data, we introduce a method which works directly in the projection domain, using parallel and fan beam projection geometries. We show that any affine deformation can be analytically compensated, and we develop an efficient multiscale estimation framework based on the normalized cross correlation. The accuracy of the approach is verified using simulated and experimental data, and we demonstrate that the new method needs less projection angles and has a much lower computational complexity as compared to approaches based on the standard reconstruction techniques.
|
|
| 7. |
- Märdla, Silja, et al.
(författare)
-
From discrete gravity survey data to a high-resolution gravity field representation in the Nordic-Baltic region
- 2017
-
Ingår i: Marine Geodesy. - : Informa UK Limited. - 0149-0419 .- 1521-060X. ; 40:6, s. 416-453
-
Tidskriftsartikel (refereegranskat)abstract
- The deduction of a regularly spaced gravity anomaly grid from scattered survey data is studied, addressing mainly two aspects: reduction of gravity to anomalies and subsequent interpolation by various methods. The problem is illustrated in a heterogeneous study area and contrasting test areas including mountains, low terrains, and a marine area. Provided with realistic error estimates, Least Squares Collocation interpolation of Residual Terrain Model anomalies yields the highest quality gravity grid. In most cases, the Bouguer reduction and other interpolation methods tested are equally viable. However, spline-based interpolation should be avoided in marine areas with trackwise survey data.
|
|
| 8. |
- Reinhard, René, et al.
(författare)
-
The Use and Usage of Virtual Reality Technologies in Planning and Implementing New Workstations
- 2020
-
Ingår i: DHM2020. - Amsterdam : IOS Press. - 9781643681047 - 9781643681054 ; , s. 388-397
-
Konferensbidrag (refereegranskat)abstract
- Virtual reality (VR) technologies can support the planning and implementation of new workstations in various industry sectors, including in automotive assembly. Starting in the early planning stages, VR can help in identifying potential problems of new design ideas, e.g. through ergonomics analyses. Designers can then quickly change the virtual representations of new workstations to test solutions for the emerging difficulties. For this purpose, the actions and motions of prospective workers can be captured while they perform the work tasks in VR. The information can also be used as input for digital human modelling (DHM) tools, to instruct biomechanical human models. The DHM tools can then construct families of manikins that differ on anthropometric characteristics, like height, to simulate work processes. This paper addresses both existing technologies for gathering data on human actions and motions during VR usage and ways in which these data can be used to assist in designing new workstations. Here, a novel approach to translate a VR user’s actions into instructions for DHM tools through an event-based instruction sampling method is presented. Further, the challenges for utilizing VR are discussed through an industrial use case of the manual assembly of flexible cables in an automotive context.
|
|
| 9. |
- Timmen, Ludger, et al.
(författare)
-
Observing Fennoscandian Gravity Change by Absolute Gravimetry
- 2006
-
Ingår i: International Association of Geodesy Symposia, Vol. 131, Geodetic Deformation Monitoring: From Geophysical to Engineering Roles. ; , s. 193-199
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- The Nordic countries Norway, Sweden, Denmark and Finland are a key study region for the research of glacial isostasy, and, in addition, it offers a unique opportunity for validating and testing the results of the GRACE experiment. Over a period of five years, the expected life time of GRACE, a temporal geoid variation of 3.0 mm is expected in the centre of the Fennoscandian land uplift area, corresponding to a gravity change of about 100 nm/s2. This is expected to be within the detection capabilities of GRACE. With terrestrial absolute gravimetry, the gravity change due to the land uplift can be observed with an accuracy of ±10 to 20 nm/s2 for a 5-year period. Thus, the terrestrial insitu observations (ground-truth) may be used to validate and test the GRACE results.Since 2003, absolute gravity measurements have been performed in Fennoscandia at about 30 stations covering Norway, Sweden, Finland and Denmark. Four groups with FG5 absolute gravimeters (BKG, FGI, IfE, UMB) are engaged to survey the uplift network annually by a mutually controlled procedure. Nearly all absolute stations are colocated with permanent GPS stations. From the 2003 and 2004 comparisons between the instruments, an overall accuracy of ±30 nm/s2 is indicated for a single absolute gravimeter and a single station determination. This is in full agreement with the project goal.
|
|
| 10. |
- Wang, Yan Ming, et al.
(författare)
-
Colorado geoid computation experiment : overview and summary
- 2021
-
Ingår i: Journal of Geodesy. - : Springer. - 0949-7714 .- 1432-1394. ; 95:12
-
Tidskriftsartikel (refereegranskat)abstract
- The primary objective of the 1-cm geoid experiment in Colorado (USA) is to compare the numerous geoid computation methods used by different groups around the world. This is intended to lay the foundations for tuning computation methods to achieve the sought after 1-cm accuracy, and also evaluate how this accuracy may be robustly assessed. In this experiment, (quasi)geoid models were computed using the same input data provided by the US National Geodetic Survey (NGS), but using different methodologies. The rugged mountainous study area (730 km x 560 km) in Colorado was chosen so as to accentuate any differences between the methodologies, and to take advantage of newly collected GPS/leveling data of the Geoid Slope Validation Survey 2017 (GSVS17) which are now available to be used as an accurate and independent test dataset. Fourteen groups from fourteen countries submitted a gravimetric geoid and a quasigeoid model in a 1' x 1' grid for the study area, as well as geoid heights, height anomalies, and geopotential values at the 223 GSVS17 marks. This paper concentrates on the quasigeoid model comparison and evaluation, while the geopotential value investigations are presented as a separate paper (Sanchez et al. in J Geodesy 95(3):1. https://doi.org/10.1007/s00190-021-01481-0, 2021). Three comparisons are performed: the area comparison to show the model precision, the comparison with the GSVS17 data to estimate the relative accuracy of the models, and the differential quasigeoid (slope) comparison with GSVS17 to assess the relative accuracy of the height anomalies at different baseline lengths. The results show that the precision of the 1' x 1' models over the complete area is about 2 cm, while the accuracy estimates along the GSVS17 profile range from 1.2 cm to 3.4 cm. Considering that the GSVS17 does not pass the roughest terrain, we estimate that the quasigeoid can be computed with an accuracy of similar to 2 cm in Colorado. The slope comparisons show that RMS values of the differences vary from 2 to 8 cm in all baseline lengths. Although the 2-cm precision and 2-cm relative accuracy have been estimated in such a rugged region, the experiment has not reached the 1-cm accuracy goal. At this point, the different accuracy estimates are not a proof of the superiority of one methodology over another because the model precision and accuracy of the GSVS17-derived height anomalies are at a similar level. It appears that the differences are not primarily caused by differences in theory, but that they originate mostly from numerical computations and/or data processing techniques. Consequently, recommendations to improve the model precision toward the 1-cm accuracy are also given in this paper.
|
|
