Blar i forfatter "Hanssen, Alfred"

Viser treff 1-11 av 11

    • Acoustic generation of underwater cavities - Comparing modeled and measured acoustic signals generated by seismic air gun arrays 

      Khodabandeloo, Babak; Landrø, Martin; Hanssen, Alfred (Journal article; Tidsskriftartikkel; Peer reviewed, 2017-04-14)
      Underwater vapor cavities can be generated by acoustic stimulation. When the acoustic signals from several air guns are reflected from the sea surface, the pressure drop at some locations is sufficient for cavity growth and subsequent collapse. In this paper the generation of multiple water vapor cavities and their collapses are numerically modeled and the results are validated by comparing with ...

    • Cenozoic uplift and erosion of the Norwegian Barents Shelf – A review 

      Lasabuda, Amando Putra Ersaid; Johansen, Nora; Laberg, Jan Sverre; Faleide, Jan Inge; Senger, Kim; Rydningen, Tom Arne; Patton, Henry; Knutsen, Stig-Morten; Hanssen, Alfred (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-03-23)
      Uplift and erosion are complex phenomena in terms of their governing processes, precise timing and exact magnitude. The intricate relationship between different geodynamic processes leading to uplift may increase uncertainties in estimating spatial and temporal patterns. Sediment distribution from uplifted (and eroded) topography and the corresponding paleoenvironmental reconstructions require ...

    • Imaging Sea Ice Structure by Remote Sensing Sensors 

      Eltoft, Torbjørn; Doulgeris, Anthony Paul; Brekke, Camilla; Solbø, Stian; Gerland, Sebastian; Hanssen, Alfred (Journal article; Tidsskriftartikkel; Peer reviewed, 2015-06-14)
      This paper will investigate how new developments in remote sensing and sensor technologies can be applied to image the structure of the sea ice surface. Both segmentation of multipolarimetric synthetic aperture radar images and strategies for the analyses of polarimetric SAR data of sea ice are addressed. The analysis is based on a Radarsat 2 PolSAR scene of from the Fram Strait in September ...

    • Long-term analysis of cryoseismic events and associated ground thermal stress in Adventdalen, Svalbard 

      Romeyn, Rowan Peter; Hanssen, Alfred; Köhler, Andreas (Journal article; Tidsskriftartikkel; Peer reviewed, 2022-05-25)
      The small-aperture Spitsbergen seismic array (SPITS) has been in continuous operation at Janssonhaugen for decades. The high-Arctic location in the Svalbard archipelago makes SPITS an ideal laboratory for the study of cryoseisms, a nontectonic class of seismic events caused by freeze processes in ice, ice–soil, and ice–rock materials. We extracted a catalog of > 100 000 events from the nearly ...

    • Microphone recording of flexural waves for estimation of lake ice thickness 

      Romeyn, Rowan Peter; Hanssen, Alfred (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-04-20)
      In this study we took an intentionally low-tech approach, aiming to estimate key physical parameters of lake ice using a single, inexpensive microphone. We consider this approach highly relevant to the issue of transport safety and the relatively high number of accidents involving breakthrough failure of thin ice underlines the importance of this topic. We conducted a range of experiments on three ...

    • A multi-source-to-sink system in a dynamic plate tectonic setting: the Cenozoic of the Barents Sea, Norwegian Arctic 

      Lasabuda, Amando P. E.; Chiarella, Domenico; Sømme, Tor Oftedal; Hanssen, Alfred; Laberg, Jan Sverre; Rydningen, Tom Arne; Patton, Henry (Conference object; Konferansebidrag, 2022)
      <p>When multiple source areas are located on a continuously moving plate margin relative to a sink, the signal propagation in the source-to-sink system may vary significantly in time and space. How fast and severe the impact of tectonics and climate is on sediment erosiontransfer-deposition in this dynamic setting is still not well understood. Similarly, how do we quantify the relative sediment ...

    • The Multivariate Normal Inverse Gaussian distribution: EM-estimation and analysis of synthetic aperture sonar data 

      Øigård, Tor Arne; Hanssen, Alfred; Hansen, Roy Edgar (Journal article; Tidsskriftartikkel; Peer reviewed, 2004-09)
      The heavy-tailed Multivariate Normal Inverse Gaussian (MNIG) distribution is a recent variance-mean mixture of a multivariate Gaussian with a univariate inverse Gaussian distribution. Due to the complexity of the likelihood function, parameter estimation by direct maximization is exceedingly difficult. To overcome this problem, we propose a fast and accurate multivariate ExpectationMaximization (EM) ...

    • Paleobathymetric reconstructions of the SW Barents Seaway and their implications for Atlantic–Arctic ocean circulation 

      Lasabuda, Amando P. E.; Hanssen, Alfred; Laberg, Jan Sverre; Faleide, Jan Inge; Patton, Henry; Abdelmalak, Mohamed Mansour; Rydningen, Tom Arne; Kjølhamar, Bent (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-06-29)
      Unravelling past, large-scale ocean circulation patterns is crucial for deciphering the longterm global paleoclimate. Here we apply numerical modelling to reconstruct the detailed paleobathymetry-topography of the southwestern inlet of the Barents Seaway that presently connects the Atlantic and Arctic oceans. Subaerial topography was likely enough to block Atlantic Water from entering the Barents ...

    • Passive seismic recording of cryoseisms in Adventdalen, Svalbard 

      Romeyn, Rowan; Hanssen, Alfred; Ruud, Bent Ole; Stemland, Helene Meling; Johansen, Tor Arne (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-01-20)
      A series of transient seismic events were discovered in passive seismic recordings from 2-D geophone arrays deployed at a frost polygon site in Adventdalen, Svalbard. These events contain a high proportion of surface wave energy and produce high-quality dispersion images using an apparent offset re-sorting and inter-trace delay minimisation technique to locate the seismic source, followed by ...

    • Sea ice thickness from air-coupled flexural waves 

      Romeyn, Rowan; Hanssen, Alfred; Ruud, Bent Ole; Johansen, Tor Arne (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-06-28)
      Air-coupled flexural waves (ACFWs) appear as wave trains of constant frequency that arrive in advance of the direct air wave from an impulsive source travelling over a floating ice sheet. The frequency of these waves varies with the flexural stiffness of the ice sheet, which is controlled by a combination of thickness and elastic properties. We develop a theoretical framework to understand these ...

    • Underexplored continental shelf gateways: timing, mechanisms and role of SW Barents Sea Gateway, Norwegian Arctic 

      Lasabuda, Amando P. E.; Hanssen, Alfred; Laberg, Jan Sverre; Rydningen, Tom Arne; Patton, Henry; Faleide, Jan Inge; Abdelmalak, Mohamed Mansour; Kjølhamar, Bent (Conference object; Konferansebidrag, 2022)
      Ocean gateways connecting ocean basins are crucial for water and heat circulation, which influence global temperature, climate evolution and sediment distribution. While deep-water gateways have been a major research focus by the community, very little attention has been drawn to shallower gateways located on the continental shelves, where such circulation also takes place. In this study, we investigate ...