Viser treff 801-820 av 1286

    • Universality of Poisson-driven plasma fluctuations in the Alcator C-Mod scrape-off layer 

      Theodorsen, Audun; Garcia, Odd Erik; Kube, Ralph; LaBombard, Brian; Terry, James L. (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-12-18)
      Large-amplitude, intermittent fluctuations are ubiquitous in the boundary region of magnetically confined plasmas and lead to detrimental plasma-wall interactions in the nextgeneration, high duty cycle fusion power experiments. Using gas puff imaging data time series from the scrape-off layer in the Alcator C-Mod device, it is here demonstrated that the large-amplitude fluctuations can be described ...
    • Effect of Wind Direction and Incidence Angle on Polarimetric SAR Observations of Slicked and Unslicked Sea Surfaces 

      Skrunes, Stine; Brekke, Camilla; Jones, Cathleen Elaine; Espeseth, Martine; Holt, Benjamin (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-05-12)
      The objective of this paper is to investigate the dependency of oil spill observations in polarimetric SAR data on imaging geometry, i.e., on incidence angle and look direction relative to the wind. The study is based on quad-polarization data acquired by the Uninhabited Aerial Vehicle Synthetic Aperture Radar over experimental oil slicks under relatively high winds of 10–12 m/s over an 8-hour period. ...
    • Measurement of Oil Slick Transport and Evolution in the Gulf of Mexico using L-band Synthetic Aperture Radar 

      Jones, Cathleen; Espeseth, Martine; Holt, Benjamin; Brekke, Camilla (Journal article; Tidsskriftartikkel, 2018-06)
      The transport and evolution of a mineral oil slick originating at a seep in the Gulf of Mexico approximately 16 km offshore of the mouth of the Mississippi River is measured using a series of images acquired at 40 minute intervals with the Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR), an L-band, high resolution, high signal-to-noise instrument operated by the U.S. National Aeronautics ...
    • Iceberg detection in open water and sea ice using C-band radar polarimetry 

      Akbari, Vahid; Brekke, Camilla (Journal article; Tidsskriftartikkel; Peer reviewed, 2017-12-04)
      Icebergs can cause a significant danger for shipping, offshore oil exploration, and undersea or subsea pipelines and production facilities. Synthetic aperture radar (SAR) is very valuable tool of detecting and monitoring icebergs in the often dark and cloud-covered polar regions. Detection of small icebergs floating in nonhomegeous sea clutter environments is a challenging task in remote sensing. ...
    • Relating Photoelectrochemistry and Wettability of Sputtered Cu- and N-Doped TiO<sub>2</sub> Thin Films via an Integrated Approach 

      Garlisi, Corrado; Lai, Chia-Yun; George, Leslie; Chiesa, Matteo; Palmisano, Giovanni (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-06-06)
      We present here an integrated study of the photoelectrochemical and hydrophilic properties of sputtered TiO<sub>2</sub> thin films, enhanced by means of nitrogen (N) and copper (Cu) doping. We investigated the effect that doping has on both photoelectrochemical efficiency and surface properties by employing a variety of techniques spanning from impedance electrochemical impedance spectroscopy to ...
    • The evolution in graphitic surface wettability with first-principles quantum simulations: the counterintuitive role of water 

      Lu, Jin-You; Lai, Chia-Yun; Almansoori, Ibraheem; Chiesa, Matteo (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-08-08)
      The surface wettability of graphite has gained a lot of interest in nanotechnology and fundamental studies alike, but the types of adsorptions that dominate its time resolved surface property variations in ambient environment are still elusive. Prediction of the intrinsic surface wettability of graphite from first-principles simulations offers an opportunity to clarify the overall evolution. In this ...
    • Discerning the Contribution of Morphology and Chemistry in Wettability Studies 

      Sloyan, Karen; Lai, Chia-Yun; Lu, Jin-You; Alfakes, Boulos; Al Hassan, Saeed; Almansouri, Ibraheem; Dahlem, Marcus S; Chiesa, Matteo (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-07-15)
      The wetting behavior of homogeneous systems is now well understood at the macroscopic scale. However, this understanding offers little predictive power regarding wettability when mesoscopic chemical and morphological heterogeneities come into play. The fundamental interest in the effect of heterogeneity on wettability is derived from its high technological relevance in several industries, including ...
    • Arctic Sea Ice Characterization using Spaceborne Fully Polarimetric L-, C- and X-Band SAR with Validation by Airborne Measurements 

      Singha, Suman; Johansson, Malin; Hughes, Nick; Hvidegaard, Sine; Skourup, Henriette (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-04-26)
      In recent years, spaceborne synthetic aperture radar (SAR) polarimetry has become a valuable tool for sea ice analysis. Here, we employ an automatic sea ice classification algorithm on two sets of spatially and temporally near coincident fully polarimetric acquisitions from the ALOS-2, Radarsat-2, and TerraSAR-X/TanDEM-X satellites. Overlapping coincident sea ice freeboard measurements from airborne ...
    • An Improved Spatial and Temporal Reflectance Unmixing Model to Synthesize Time Series of Landsat-Like Images 

      Ma, Jianhang; Wenjuan, Zhang; Marinoni, Andrea; Lianru, Gao; Bing, Zhang (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-08-31)
      The trade-off between spatial and temporal resolution limits the acquisition of dense time series of Landsat images, and limits the ability to properly monitor land surface dynamics in time. Spatiotemporal image fusion methods provide a cost-efficient alternative to generate dense time series of Landsat-like images for applications that require both high spatial and temporal resolution images. The ...
    • Sea ice segmentation using Tandem-X pursuit mono static and alternative bistatic modes 

      Yitayew, Temesgen Gebrie; Doulgeris, Anthony Paul; Eltoft, Torbjørn; Dierking, Wolfgang Fritz Otto; Brekke, Camilla; Rösel, Anja (Journal article; Tidsskriftartikkel; Peer reviewed, 2017-12-04)
      In this paper we investigate interferometric pairs of SAR images acquired by Tandem-X with the monostatic pursuit and the alternative bistatic modes for sea ice segmentation. The individual SAR images are modelled as non-Gaussian, and from the modelled data different features are extracted, stacked together and clustered. The interferometric coherence is regarded as an additional feature and utilized ...
    • First Observations of Recurring HF-Enhanced Topside Ion Line Spectra Near the Fourth Gyroharmonic 

      Rexer, Theresa; Gustavsson, Björn Johan; Leyser, Thomas; Rietveld, Michael T; Yeoman, Tim; Grydeland, Tom (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-09-28)
      We present first incoherent scatter radar observations of systematically recurring, high‐frequency (HF)‐enhanced ion line spectra at the topside F‐region ionosphere, during magnetic field aligned HF pumping in an O‐mode polarization. The European Incoherent Scatter UHF radar was directed in magnetic zenith on 9–11 March 2016 while stepping the pump frequency across the double resonance of the fourth ...
    • Evaluating CM-SAF solar radiation CLARA-A1 and CLARA-A2 datasets in Scandinavia 

      Babar, Bilal; Graversen, Rune; Boström, Tobias (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-05-26)
      Estimating/retrieving solar radiation through satellite-based remote sensing provides larger spatial coverage compared to other methods. Accurate estimates of incoming solar radiation is important when planning new solar energy installations. In addition, these estimates are also used in climate studies. Geostationary satellites are ideal for estimating solar radiation but cannot be used for high ...
    • The effect of vertical mixing on the horizontal drift of oil spills 

      Röhrs, Johannes; Dagestad, Knut-Frode; Asbjørnsen, Helene; Nordam, Tor; Skancke, Jørgen; Jones, Cathleen; Brekke, Camilla (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-12-21)
      Vertical and horizontal transport mechanisms for marine oil spills are investigated using numerical model simulations. To realistically resolve the 3-D development of a spill on the ocean surface and in the water column, recently published parameterizations for the vertical mixing of oil spills are implemented in the open-source trajectory framework OpenDrift (https://doi.org/10.5281/zenodo.1300358, ...
    • Assessing polarimetric SAR sea-ice classifications using consecutive day images 

      Moen, Mari-Ann; Anfinsen, Stian Normann; Doulgeris, Anthony Paul; Renner, Angelika; Gerland, Sebastian (Journal article; Tidsskriftartikkel; Peer reviewed, 2015)
      This paper investigates automatic segmentation and classification of C-band, polarimetric synthetic aperture radar (SAR) satellite images of Arctic sea ice under freezing conditions prior to melt. The objective is to investigate the robustness of the results obtained under slightly varying environmental conditions and different viewing geometries. Initially, three geographically overlapping SAR ...
    • Investigation of Thermo-Optical Phase Modulator for Chip Based Structured Illumination Microscopy 

      Das, Sourov Kumar (Master thesis; Mastergradsoppgave, 2018-11-21)
      Optical nanoscopy is an emerging field and enables super-resolution of biological cells. Among the existing nanoscopy techniques, structured illumination microscopy (SIM) is most promising candidate for live cell imaging due to its high-imaging speed, limited photo-toxicity and its suitability with most commonly used fluorophore. One of research focus of the optics group at the department is to ...
    • Derivation of vertical wavelengths of gravity waves in the MLT-region from multispectral airglow observations 

      Schmidt, Carsten; Dunker, Tim; Lichtenstern, Sabrina; Scheer, Jürgen; Wüst, Sabine; Hoppe, Ulf-Peter; Bittner, Michael (Journal article; Tidsskriftartikkel; Peer reviewed; Preprint; Manuskript, 2018-03-06)
      <p>We present the derivation of gravity wave vertical wavelengths from OH airglow observations of different vibrational transitions. It utilizes small phase shifts regularly observed between the OH(3-1) and OH(4-2) intensities in the spectra of the GRIPS (GRound-based Infrared P-branch Spectrometer) instruments, which record the OH airglow emissions in the wavelength range from 1.5  μm to 1.6  μm ...
    • Scenario-based modelling of the potential for solar energy charging of electric vehicles in two Scandinavian cities 

      Good, Clara; Shepero, Mahmoud; Munkhammar, Joakim; Boström, Tobias (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-11-19)
      In order to contribute to the reduction of greenhouse gas emissions, electric vehicles (EVs) should be charged using electricity from renewable energy sources. This paper describes a study of photovoltaics (PV) utilization for EV charging in two Scandinavian cities: Tromsø in Norway and Uppsala in Sweden, with the objective to evaluate self-sufficiency and self-consumption. The suitable areas ...
    • An unsupervised method for equivalent number of looks estimation in complex SAR scenes 

      Hu, Dingsheng; Doulgeris, Anthony Paul; Qiu, Xiaolan (Journal article; Tidsskriftartikkel; Peer reviewed, 2015-11-12)
      This paper introduces a novel unsupervised estimator of equivalent number of looks (ENL) that can be applied to an arbitrary image. It avoids the assumption that homogeneous speckle will dominate the investigated image that is followed by current unsupervised ENL estimators but not always valid, especially for the complex SAR scenes with high mixture and texture. Incorporating the statistical ...
    • Aspects of model-based decompositions in radar polarimetry 

      Doulgeris, Anthony Paul; Eltoft, Torbjørn (Journal article; Tidsskriftartikkel; Peer reviewed, 2015-11-12)
      In this paper, we further analyse the problem that polarimetric target decomposition methods in general have more physical parameters than equations, making the decomposition under-determined and hence have no unique solution. The common approach to get around this problem is to make certain assumptions, thus fixing one or more parameters, allowing the other free parameters to be solved from the set ...
    • Incorporating Incidence Angle Variation into Sar Image Segmentation 

      Doulgeris, Anthony Paul; Cristea, Anca (Journal article; Tidsskriftartikkel; Peer reviewed, 2018)
      We present a new approach for incorporating incidence angle derived synthetic aperture radar (SAR) brightness variation directly into SAR image analysis. This approach is unique in that the incidence angle dependency is modeled explicitly into the probability density function rather than an image-wide pre-processing ‘correction’. It can then be used for supervised and unsupervised image analysis, ...