| 1. |
- Björk, Göran, 1956, et al.
(författare)
-
Flow of Canadian Basin Deep Water in the Western Eurasian Basin of the Arctic Ocean
- 2010
-
Ingår i: Deep Sea Research. - : Elsevier BV. - 0967-0637 .- 1879-0119. ; 57:4, s. 577-586
-
Tidskriftsartikel (refereegranskat)abstract
- The LOMROG 2007 expedition targeted the previously unexplored southern part of the Lomonosov Ridge north of Greenland together with a section from the Morris Jesup Rise to Gakkel Ridge. The oceanographic data shows that Canadian Basin Deep Water (CBDW) passes the Lomonosov Ridge in the area of the Intra Basin close to the North Pole and then continues along the ridge towards Greenland and further along its northernmost continental slope. The CBDW is clearly evident as a salinity maximum and oxygen minimum at a depth of about 2000 m. The cross slope sections at the Amundsen Basin side of the Lomonosov Ridge and further south at the Morris Jesup Rise show a sharp frontal structure higher up in the water column between Makarov Basin water and Amundsen Basin water. The frontal structure continues upward into the Atlantic Water up to a depth of about 300 m. The observed water mass division at levels well above the ridge crest indicates a strong topographic steering of the flow and that different water masses tend to pass the ridge guided by ridge-crossing isobaths at local topographic heights and depressions. A rough scaling analysis shows that the extremely steep and sharply turning bathymetry of the Morris Jesup Rise may force the boundary current to separate and generate deep eddies.
|
|
| 2. |
- Carvajal, Gisela, 1983, et al.
(författare)
-
Correlation between Synthetic Aperture Radar Surface Winds and Deep Water Velocity in the Amundsen Sea, Antarctica
- 2013
-
Ingår i: Remote Sensing. - : MDPI AG. - 2072-4292. ; 5:8, s. 4088-4106
-
Tidskriftsartikel (refereegranskat)abstract
- The recent observed thinning of the glacier ice shelves in the Amundsen Sea (Antarctica) has been attributed to warm deep currents, possibly induced by along-coast winds in the vicinity of the glacial ice sheet. Here, high resolution maps of wind fields derived from Synthetic Aperture Radar (SAR) data have been studied and correlated with subsurface measurements of the deep water velocities in the Amundsen Sea area. Focus is on periods with low ice coverage in 2010 and 2011. In 2010, which had comparatively low ice coverage, the results indicate a more rapid response to wind forcing in the deep currents than in 2011. The SAR wind speed maps have better spatial resolution than available reanalysis data, and higher maximum correlation was obtained with SAR data than with reanalysis data despite the lower temporal resolution. The maximum correlation was R = 0.71, in a direction that is consistent with wind-driven Ekman theory. This is significantly larger than in previous studies. The larger correlation could be due to the better spatial resolution or the restriction to months with minimum ice coverage. The results indicate that SAR is a useful complement to infer the subsurface variability of the ocean circulation in remote areas in polar oceans.
|
|
| 3. |
- Berg, Anders, 1983, et al.
(författare)
-
Comparison between SAR derived sea ice displacement and hindcasts by the operational ocean model HIROMB
- 2013
-
Ingår i: Proceedings of the IEEE International Geoscience and Remote Sensing Symposium (IGARSS), Melbourne, Australia, July 21-26, 2013. - 9781479911141 ; , s. 3630-3633
-
Konferensbidrag (refereegranskat)abstract
- The purpose of this paper is to compare measurements of sea ice displacement from SAR imagery with ice floe drift trajectories modeled by the operational ocean circulation model HIROMB. The study examines the ice movement in the Fram Strait during a two-week period in April, 2011. The results indicate that the HIROMB model overestimates the drift speed by a factor 1 - 2.5, which may be attributed to an underestimated thickness of the ice. The model data also exhibit a directional offset in the positive clockwise direction of 10 - 30 degrees over the whole study region. The results of this study may be used to direct the model development and improve the model initialization.
|
|
| 4. |
- Berg, Anders, 1983, et al.
(författare)
-
Demonstration of X-Band SAR Interferometry over Baltic Fast Ice
- 2013
-
Ingår i: Proceedings of Earth Observation and Cryosphere Science, 13 - 16 November 2012, Frascati, Italy. - 1609-042X. - 9789290922766 ; 2013
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This study utilizes X-band SAR images acquired by theCosmo-SkyMed satellite constellation to map fast icedeformation at high spatial resolution. Twointerferometric acquisitions were performed in themiddle of the ice season in 2012 and with a temporalbaseline of 24 hours. The first interferogram revealsdeformation of the fast ice which is being forced by theramming drift ice. The drift ice moved towards the fastice with up to 600 m based on phase correlationmeasurements. The second interferogram shows a ratherlow fringe rate over the fast ice with fringes beingaligned along the coastline. Emerging cracks are easilyidentified with the associated phase discontinuities. It isalso observed that the backscatter and coherence levelsare connected in certain regions.
|
|
| 5. |
- Berg, Anders, 1983, et al.
(författare)
-
Evaluation of a sea ice algorithm for SAR data from the Bay of Bothnia
- 2010
-
Ingår i: Proceedings of the Third International Workshop SeaSAR 2010, 25-29 January 2010, Frascati, Italy. - 1609-042X. - 9789292212438 ; ESA SP-679
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A sea ice drift algorithm published by M. Thomas et. al.(2008) has been implemented and evaluated. Input tothe algorithm is Synthetic Aperture Radar (SAR)images, which are processed using phase correlation ina multi-resolution processing system. The algorithm hasbeen tested with horizontally co-polarized (HH)ENVISAT ASAR Wide Swath images andRADARSAT-2 ScanSAR images. The possible benefitsof using cross-polarized (HV) RADARSAT-2 ScanSARdata are investigated, and initial testing of the algorithmfor L-band SAR data from ALOS PALSAR has beendone.The validity of the produced motion fields has beentested in three different ways. Most of the SAR imagesin this analysis were acquired over the Bay of Bothnia.Five meteorological stations located in this region havebeen collecting wind data with a temporal resolution ofthree hours. It is confirmed that the wind data correlateswith the derived sea ice motion. Another source ofvalidation data that has been used is the daily ice chartspublished by the Swedish Meteorological andHydrological Institute (SMHI). The third method usedfor validation is straightforward, visual tracking of seaice features.The algorithm is facing some difficulties when it comesto ice tracking close to the shoreline, in archipelagoesetc, since the motionless solution will be favoured. Itcan however be suppressed by filtering areas of land.This addition gives a more robust algorithm.
|
|
| 6. |
- Berg, Anders, 1983, et al.
(författare)
-
Evaluation of sea ice concentration algorithm for SAR data from the Bay of Bothnia
- 2010
-
Ingår i: Proceedings of the ESA Living Planet Symposium 2010, 28 June - 2 July 2010, Bergen, Norway.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A sea ice coverage algorithm has been developed for C-band SAR data. It has been tested with images from ENVISAT ASAR in Wide Swath Mode (WSM) over the Bay of Bothnia and the Svalbard region. The algorithm is based on autocorrelation in combination with Otsu’s thresholding method. Ice charts over the Bay of Bothnia have been used for a qualitative validation of the results.
|
|
| 7. |
- Berg, Anders, 1983, et al.
(författare)
-
Investigation of a Hybrid Algorithm for Sea Ice Drift Measurements Using Synthetic Aperture Radar Images
- 2014
-
Ingår i: IEEE Transactions on Geoscience and Remote Sensing. - 0196-2892 .- 1558-0644. ; 52:8, s. 5023 - 5033
-
Tidskriftsartikel (refereegranskat)abstract
- Areal matching by phase correlation and feature tracking are two complementary methods used to measure sea ice drift between synthetic aperture radar images. This paper evaluates a new algorithm that combines the two methods. Areal matching is improved by new methods to handle large motions and rotated ice. It is shown that areal rotation can be resolved using a frequency-domain approach. Image segmentation is a prerequisite for feature tracking and achieved by a new method that performs better than Otsu's method for two-component Gaussian mixture distributions. A circular weighted median filter is found to be suitable for the filtering of the motion field. The algorithm is evaluated through a thorough analysis of the response and sensitivity to various algorithm settings. The accuracy of the algorithm varies by up to 50% for one image pair within the studied range of parameter settings, thus indicating the need for a proper initialization of the algorithm.
|
|
| 8. |
- Berg, Anders, 1983, et al.
(författare)
-
Observations and Analysis of Sea Ice Motion with the Ice Buoy DRIVA during the 2010 Spring Field Campaign in the Bay of Bothnia
- 2011
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The ice drift buoy DRIVA is tested for the first time in the environment for which it was designed. The communication with the buoy via satellite phone is working well. Temperatures could be read during the entire test period, and except from an unexplained loss of GPS data during 20 days, the GPS position was transmitted as expected. The rotary encoders did not function properly during the campaign. A sea ice drift algorithm is validated against the buoy data using ten image pairs acquired by the C‐band SAR satellite ENVISAT. The accuracy of the algorithm decreases with time and highest accuracy is achieved with the first three image pairs. For the first image pair, the computed translation differs by only 160 m from the translation measured by the buoy, which is a good result considering the pixel resolution of approximately 150 m. The root mean square error of the algorithm for the first three image pairs is 5% for the ice speed and 4 degrees for the direction of the ice. The decreasing accuracy can be related to an increase of melting during the campaign. The sea ice is very dynamic during the period, making the images very different. Large ice floes break into smaller pieces after a short time. As the ice floes melt and get smaller, rotation increases, and the shapes of the ice floes are not preserved. It appears that the buoy floats within a streak of slush ice during the last days of the time period. Tracking of the ice is more difficult under such circumstances, because the contours of an area of slush ice are constantly changing.
|
|
| 9. |
- Berg, Anders, 1983, et al.
(författare)
-
SAR Algorithm for Sea Ice Concentration - Evaluation for the Baltic Sea
- 2012
-
Ingår i: IEEE Geoscience and Remote Sensing Letters. - 1558-0571 .- 1545-598X. ; 9:5, s. 938 - 942
-
Tidskriftsartikel (refereegranskat)abstract
- A new sea ice concentration algorithm has been developed for C-band synthetic aperture radar data. Detailed autocorrelation statistics are derived and adopted by the algorithm, and a neural network is utilized for training against 41 sea ice charts. The charts are produced by ice analysts at the Swedish Ice Service and cover the Baltic Sea. The classification of open water pixels is accurate to 94% on average, and the classification of sea ice pixels has an accuracy of 87%. This results in a root-mean-square error of 6.7 percentage points in estimating the sea ice concentration.
|
|
| 10. |
- Berndt, Sonja I., et al.
(författare)
-
Genome-wide meta-analysis identifies 11 new loci for anthropometric traits and provides insights into genetic architecture
- 2013
-
Ingår i: Nature Genetics. - : Springer Science and Business Media LLC. - 1061-4036 .- 1546-1718. ; 45:5, s. 501-U69
-
Tidskriftsartikel (refereegranskat)abstract
- Approaches exploiting trait distribution extremes may be used to identify loci associated with common traits, but it is unknown whether these loci are generalizable to the broader population. In a genome-wide search for loci associated with the upper versus the lower 5th percentiles of body mass index, height and waist-to-hip ratio, as well as clinical classes of obesity, including up to 263,407 individuals of European ancestry, we identified 4 new loci (IGFBP4, H6PD, RSRC1 and PPP2R2A) influencing height detected in the distribution tails and 7 new loci (HNF4G, RPTOR, GNAT2, MRPS33P4, ADCY9, HS6ST3 and ZZZ3) for clinical classes of obesity. Further, we find a large overlap in genetic structure and the distribution of variants between traits based on extremes and the general population and little etiological heterogeneity between obesity subgroups.
|
|
