Nye registreringer

  • 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, ...
  • Unsupervised Mixture-Eliminating Estimation of Equivalent Number of Looks for PolSAR Data 

    Hu, Dingsheng; Anfinsen, Stian Normann; Qiu, X; Doulgeris, Anthony Paul; Lei, Bin (Journal article; Tidsskriftartikkel; Peer reviewed, 2017-08-22)
    This paper addresses the impact of mixtures between classes on equivalent number of looks (ENL) estimation. We propose an unsupervised ENL estimator for polarimetric synthetic aperture radar (PolSAR) data, which is based on small sample estimates but incorporates a mixture-eliminating (ME) procedure to automatically assess the uniformity of the estimation windows. A statistical feature derived from ...
  • A K-Wishart Markov random field model for clustering of polarimetric SAR imagery 

    Akbari, Vahid; Moser, Gabriele; Doulgeris, Anthony Paul; Anfinsen, Stian Normann; Eltoft, Torbjørn; Serpico, Sebastian Bruno (Peer reviewed; Book; Chapter, 2011-10-20)
    A clustering method that combines an advanced statistical distribution with spatial contextual information is proposed for multilook polarimetric synthetic aperture radar (PolSAR) data. It is based on a Markov random field (MRF) model that integrates a K-Wishart distribution for the PolSAR data statistics conditioned to each image cluster and a Potts model for the spatial context. Specifically, the ...
  • A solvable model for the basic properties of a simple magnetized plasma torus 

    Fredriksen, Åshild; Pécseli, Hans; Trulsen, Jan Karsten (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-07-11)
    A simple magnetized plasma torus is modeled by using a 'top-hat' density variation. The benefit of this simplification is an exactly solvable model, allowing for a few additions, such as an externally maintained parabolic steady state potential variation imposed on the plasma. The combined effects of the resulting plasma rotation and the plasma polarization due to magnetic field gradient particle ...
  • Bistatic Observations of the Ocean Surface with HF Radar, Satellite and Airborne Receivers 

    Bernhardt, Paul A.; Siefring, Carl; Briczinski, Stanley; Vierinen, Juha; Miller, Ethan; Howarth, Andrew; James, H. Gordon; Blincoe, Eugene (Peer reviewed; Book; Chapter, 2017-12-25)
    A new concept has been developed which can view vast regions of the Earth's surface. Ground HF transmissions are reflected by the ionosphere to illuminate the ocean over a few thousand kilometers. HF receivers detect the radio waves scattered by the sea and land surface. Using the theory of radio wave scatter from ocean surfaces, the HF data is then processed to yield the directional wave-height ...
  • Machine Learning Automatic Model Selection Algorithm for Oceanic Chlorophyll-a Content Retrieval 

    Blix, Katalin; Eltoft, Torbjørn (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-05-17)
    Ocean Color remote sensing has a great importance in monitoring of aquatic environments. The number of optical imaging sensors onboard satellites has been increasing in the past decades, allowing to retrieve information about various water quality parameters of the world’s oceans and inland waters. This is done by using various regression algorithms to retrieve water quality parameters from remotely ...
  • Remote Sensing of Water Quality Parameters over Lake Balaton by Using Sentinel-3 OLCI 

    Blix, Katalin; Pálffy, Károly; Tóth, Viktor R.; Eltoft, Torbjørn (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-10-11)
    The Ocean and Land Color Instrument (OLCI) onboard Sentinel 3A satellite was launched in February 2016. Level 2 (L2) products have been available for the public since July 2017. OLCI provides the possibility to monitor aquatic environments on 300 m spatial resolution on 9 spectral bands, which allows to retrieve detailed information about the water quality of various type of waters. It has only been ...
  • Numerical Analysis of Microwave Scattering from Layered Sea Ice Based on the Finite Element Method 

    Xu, Xu; Brekke, Camilla; Doulgeris, Anthony Paul; Melandsø, Frank (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-08-21)
    A two-dimensional scattering model based on the Finite Element Method (FEM) is built for simulating the microwave scattering of sea ice, which is a layered medium. The scattering problem solved by the FEM is formulated following a total- and scattered-field decomposition strategy. The model set-up is first validated with good agreements by comparing the results of the FEM with those of the small ...
  • Multi-static spatial and angular studies of polar mesospheric summer echoes combining MAARSY and KAIRA 

    Chau, Jorge L.; McKay, Derek; Vierinen, Juha; La Hoz, Cesar Augusto Vergara; Ulich, Thomas; Lehtinen, Markku; Latteck, Ralph (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-07-06)
    Polar mesospheric summer echoes (PMSEs) have been long associated with noctilucent clouds (NLCs). For large ice particles sizes and relatively high ice densities, PMSEs at 3m Bragg wavelengths are known to be good tracers of the atmospheric wind dynamics and to be highly correlated with NLC occurrence. Combining the Middle Atmosphere ALOMAR Radar System (MAARSY) and the Kilpisjärvi Atmospheric Imaging ...
  • USE OF EISCAT 3D FOR OBSERVATIONS OF SPACE DEBRIS 

    Vierinen, Juha; Markkanen, Jussi; Krag, Holger; Siminski, Jan; Mancas, Alexandru (Peer reviewed; Conference object; Konferansebidrag, 2017-06)
    We investigate the capabilities of the next generation ionospheric research radar EISCAT 3D (E3D) for observations of space objects. The radar is multi-static, and is therefore capable of observing instantaneous threedimensional vector velocity and position by observing round-trip delay and Doppler shift between the transmitter and three receiver sites. The radar is to be located in Northern ...
  • Comparison between a multi-variate nudging method and the ensemble Kalman filter for sea-ice data assimilation 

    Fritzner, Sindre Markus; Graversen, Rune; Wang, Keguang; Christensen, Kai Håkon (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-04-25)
    Increasing ship traffic and human activity in the Arctic has led to a growing demand for accurate Arctic weather forecast. High-quality forecasts obtained by models are dependent on accurate initial states achieved by assimilation of observations. In this study, a multi-variate nudging (MVN) method for assimilation of sea-ice variables is introduced. The MVN assimilation method includes procedures ...

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