Nye registreringer

  • 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 ...
  • High-resolution optical nanoscopy of placental cells 

    Ahluwalia, Balpreet Singh (Journal article; Tidsskriftartikkel; Peer reviewed, 2017)
    <i>Introduction</i>: The invention of fluorescence based super-resolution optical microscopy, commonly referred to as optical nanoscopy, has provided a glimpse of its future impacts on life science and medical care. Optical nanoscopy enables study of sub-cellular nanoscale biological systems in living cells, which in past was limited to electron microscopy (in fixed cells). Optical nanoscopy provide ...
  • The Hotelling-Lawley trace statistic for change detection in polarimetric SAR data under the complex Wishart distribution 

    Akbari, Vahid; Anfinsen, Stian Normann; Doulgeris, Anthony Paul; Eltoft, Torbjørn (Journal article; Peer reviewed, 2014-01-27)
    In this paper we propose a new test statistic for unsupervised changedetectioninpolarimetricsyntheticapertureradar(PolSAR) data. We work with multilook complex (MLC) covariance matrix data, whose underlying model is assumed to be the scaled complex Wishart distribution. We use the complex kind Hotelling-Lawley (HL) trace statistic for measuring the similarity of two covariance matrices. The sampling ...
  • A change detector for polarimetric SAR data based on the relaxed Wishart distribution 

    Akbari, Vahid; Anfinsen, Stian Normann; Doulgeris, Anthony Paul; Eltoft, Torbjørn (Journal article; Tidsskriftartikkel; Peer reviewed, 2015-11-12)
    In this paper, we present an unsupervised change detection method for polarimetric synthetic aperture radar (PolSAR) images based on the relaxed Wishart distribution. Most polarimetric change detectors assume the Gaussian-based complex Wishart model for multilook covariance matrices, which is only satisfied for homogeneous areas with fully developed speckle and no texture. Liu et al. recently proposed ...
  • Multi-color imaging of sub-mitochondrial structures in living cells using structured illumination microscopy 

    Opstad, Ida Sundvor; Wolfson, Deanna; Øie, Cristina Ionica; Ahluwalia, Balpreet Singh (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-05-18)
    The dimensions of mitochondria are close to the diffraction limit of conventional light microscopy techniques, making the complex internal structures of mitochondria unresolvable. In recent years, new fluorescence-based optical imaging techniques have emerged, which allow for optical imaging below the conventional limit, enabling super-resolution (SR). Possibly the most promising SR and diffraction-limited ...
  • Light and photosynthetic microalgae: A review of cellular- and molecular-scale optical processes 

    Lehmuskero, Anni Maria; Chauton, Matilde Skogen; Boström, Tobias (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-09-08)
    Light and its interaction with microalgae are essential concerns in the context of microalgae studies. The optical properties of microalgae have a great impact on the remote sensing ocean color, underwater light distribution and biomass accumulation, to mention some areas. A deep understanding of these processes requires knowledge on both the physical light interaction mechanisms with algae, and ...
  • Comets as a possible source of nanodust in the Solar System cloud and in planetary debris discs 

    Mann, Ingrid (Journal article; Tidsskriftartikkel; Peer reviewed, 2017-05-29)
    Comets, comet-like objects and their fragments are the most plausible source for the dust in both the inner heliosphere and planetary debris discs around other stars. The smallest size of dust particles in debris discs is not known and recent observational results suggest that the size distribution of the dust extends down to sizes of a few nanometres or a few tens of nanometres. In the Solar System, ...
  • Challenges and Strategic Research Plans for Earth and Heliosphere: Research Infrastructures, Projects and Initiatives 

    Mann, Ingrid; Kauristie, Kirsti; Bamford, Ruth; McCrea, Ian; Moen, Jøran Idar; Oksavik, Kjellmar; Yamauchi, Masanori; Johnsen, Magnar Gullikstad; Turunen, Esa (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-07-24)
    We describe existing research infrastructures relevant for space weather and open issues of space weather research including the need for sustainable observation networks and for high-quality data products as basis for model development. The local relevance in Europe for studies of the ionosphere at high latitude is described. We propose as possible a way forward to sustain space weather research ...

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