Now showing items 48-67 of 400

    • Comparing SAR based short time-lag cross-correlation and Doppler derived sea ice drift velocities 

      Kræmer, Thomas; Johnsen, Harald; Brekke, Camilla; Engen, Geir (Journal article; Tidsskriftartikkel; Peer reviewed, 2017-11-23)
      This paper shows initial results from estimating Doppler radial surface velocities (RVLs) over Arctic sea ice using the Sentinel-1A (S1A) satellite. Our study presents the first quantitative comparison between ice drift derived from the Doppler shifts and drift derived using time-series methods over comparable time scales. We compare the Doppler-derived ice velocities with global positioning system ...
    • 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 ...
    • Comparison of feature based segmentation of full polarimetric SAR satellite sea ice images with manually drawn ice charts 

      Moen, Mari-Ann; Doulgeris, Anthony Paul; Anfinsen, Stian Normann; Renner, Angelika H.H.; Hughes, Nick; Gerland, Sebastian; Eltoft, Torbjørn (Journal article; Tidsskriftartikkel; Peer reviewed, 2013)
      In this paper we investigate the performance of an algorithm for automatic segmentation of full polarimetric, synthetic aperture radar (SAR) sea ice scenes. The algorithm uses statistical and polarimetric properties of the backscattered radar signals to segment the SAR image into a specified number of classes. This number was determined in advance from visual inspection of the SAR image and by ...
    • A comparison of overshoot modelling with observations of polar mesospheric summer echoes at radar frequencies of 56 and 224 MHz 

      Havnes, Ove; Pinedo Nava, Henry; La Hoz, Cesar; Senior, Andrew; Hartquist, Thomas W.; Rietveld, Michael T; Kosch, Michael J. (Journal article; Tidsskriftartikkel; Peer reviewed, 2015)
      We have compared radar observations of polar mesospheric summer echoes (PMSEs) modulated by artificial electron heating, at frequencies of 224 MHz (EISCAT VHF) and 56 MHz (MORRO). We have concentrated on 1 day of observation, lasting ~ 3.8 h. The MORRO radar, with its much wider beam, observes one or more PMSE layers all the time while the VHF radar observes PMSEs in 69% of the time. Statistically ...
    • Comparison of the orientation of small-scale electron density irregularities and F region plasma flow direction. 

      Tereshchenko, E.D.; Rietveld, Michael T.; Brekke, Asgeir; Khudukon, B.Z.; Kozlova, M.O.; Evstafiev, O.V.; Nygren, T. (Journal article; Peer reviewed; Tidsskriftartikkel, 2000)
      Results are shown from an experimental campaign where satellite scintillation was observed at three sites at high latitudes and, simultaneously, the F region plasma flow was measured by the nearby EISCAT incoherent scatter radar. The anisotropy parameters of field-aligned irregularities are determined from amplitude scintillation using a method based on the variance of the relative logarithmic ...
    • ConnNet: A Long-Range Relation-Aware Pixel-Connectivity Network for Salient Segmentation 

      Kampffmeyer, Michael C.; Dong, Nanqing; Liang, Xiaodan; Zhang, Yujia; Xing, Eric P. (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-12-14)
      Salient segmentation aims to segment out attention-grabbing regions, a critical yet challenging task and the foundation of many high-level computer vision applications. It requires semantic-aware grouping of pixels into salient regions and benefits from the utilization of global multi-scale contexts to achieve good local reasoning. Previous works often address it as two-class segmentation problems ...
    • Consensus Clustering Using kNN Mode Seeking 

      Myhre, Jonas Nordhaug; Mikalsen, Karl Øyvind; Løkse, Sigurd; Jenssen, Robert (Chapter; Bokkapittel, 2015-06-09)
      In this paper we present a novel clustering approach which combines two modern strategies, namely consensus clustering, and two stage clustering as represented by the mean shift spectral clustering algorithm. We introduce the recent kNN mode seeking algorithm in the consensus clustering framework, and the information theoretic kNN Cauchy Schwarz divergence as foundation for spectral clustering. In ...
    • Convergence of statistical moments of particle density time series in scrape-off layer plasmas 

      Kube, Ralph; Garcia, Odd Erik (Journal article; Tidsskriftartikkel; Peer reviewed, 2015)
    • Coordinated Cluster/Double Star and ground-based observations of dayside reconnection signatures on 11 February 2004 

      La Hoz, Cesar (Journal article; Tidsskriftartikkel; Peer reviewed, 2011)
      A number of flux transfer events (FTEs) were observed between 09:00 and 12:00UT on 11 February 2004, during southward and dawnward IMF, while the Cluster spacecraft array moved outbound through the northern, highaltitude cusp and dayside high-latitude boundary layer, and the Double Star TC-1 spacecraft was crossing the dayside low-latitude magnetopause into the magnetosheath south of the ecliptic ...
    • Correction and Characterization of Radio Frequency Interference Signatures in L-band Synthetic Aperture Radar Data 

      Meyer, Franz; Nicoll, Jeremy; Doulgeris, Anthony Paul (Journal article; Tidsskriftartikkel; Peer reviewed, 2013)
      Radio frequency interference (RFI) is a known issue in low-frequency radar remote sensing. In synthetic aperture radar (SAR) image processing, RFI can cause severe degradation of image quality, distortion of polarimetric signatures, and an increase of the SAR phase noise level. To address this issue, a processing system was developed that is capable of reliably detecting, characterizing, and mitigating ...
    • Corrigendum to "Development of the mesospheric Na layer at 69 degrees N during the Geminids meteor shower 2010", published in Ann.Geophys., 31, 61-73, 2013 

      Dunker, Tim; Hoppe, Ulf-Peter; Stober, Gunter; Rapp, Markus (Journal article; Tidsskriftartikkel; Peer reviewed, 2015)
    • Crash and recovery of the potential in a toroidal plasma column, as observed by generalized conditional sampling 

      Pecseli, Hans L.; Fredriksen, Åshild; Trulsen, Jan; Fredriksen, A.A. (Journal article; Tidsskriftartikkel; Peer reviewed, 2008)
    • Cross-Correlation Between Polarization Channels in SAR Imagery Over Oceanographic Features 

      Brekke, Camilla; Jones, Cathleen; Skrunes, Stine; Holt, Benjamin; Espeseth, Martine; Eltoft, Torbjørn (Journal article; Tidsskriftartikkel; Peer reviewed, 2016-05-11)
      This letter discusses cross-correlation features de- rived from near-coincident RADARSAT-2 quad-polarimetric and RISAT-1 hybrid-polarity (HP) measurements collected during the NOrwegian Radar oil Spill Experiment in 2015 (NORSE2015). We show that the imaginary part of the cross-correlation between RH and RV is an HP parallel to the real part of the cross-correlation between HH and VV earlier ...
    • Data-driven detrending of nonstationary fractal time series with echo state networks 

      Maiorino, Enrico; Bianchi, Filippo Maria; Livi, Lorenzo; Rizzi, Antonello; Sadeghian, Alireza (Journal article; Tidsskriftartikkel, 2016-12-14)
      In this paper, we propose a novel data-driven approach for removing trends (detrending) from nonstationary, fractal and multifractal time series. We consider real-valued time series relative to measurements of an underlying dynamical system that evolves through time. We assume that such a dynamical process is predictable to a certain degree by means of a class of recurrent networks called Echo ...
    • Dataverktøy til regning, skriving og tegning i naturfag 

      Haugland, Ole Anton (Book; Bok, 2007)
    • The deep kernelized autoencoder 

      Kampffmeyer, Michael C.; Løkse, Sigurd; Bianchi, Filippo Maria; Jenssen, Robert; Livi, Lorenzo (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-07-18)
      Autoencoders learn data representations (codes) in such a way that the input is reproduced at the output of the network. However, it is not always clear what kind of properties of the input data need to be captured by the codes. Kernel machines have experienced great success by operating via inner-products in a theoretically well-defined reproducing kernel Hilbert space, hence capturing topological ...
    • Deep kernelized autoencoders 

      Kampffmeyer, Michael C.; Løkse, Sigurd; Bianchi, Filippo Maria; Jenssen, Robert; Livi, Lorenzo (Peer reviewed; Book; Bok; Bokkapittel; Chapter, 2017-05-19)
      In this paper we introduce the deep kernelized autoencoder, a neural network model that allows an explicit approximation of (i) the mapping from an input space to an arbitrary, user-specified kernel space and (ii) the back-projection from such a kernel space to input space. The proposed method is based on traditional autoencoders and is trained through a new unsupervised loss function. ...
    • Deep Reinforcement Learning for Query-Conditioned Video Summarization 

      Zhang, Yujia; Kampffmeyer, Michael C.; Zhao, Xiaoguang; Tan, Min (Journal article; Tidsskriftartikkel; Peer reviewed, 2019-02-21)
      Query-conditioned video summarization requires to (1) find a diverse set of video shots/frames that are representative for the whole video, and that (2) the selected shots/frames are related to a given query. Thus it can be tailored to different user interests leading to a better personalized summary and differs from the generic video summarization which only focuses on video content. Our work targets ...
    • Delt situasjonsforståelse under søk og redning i nordområdene 

      Haugstveit, Ida Maria; Skjetne, Jan Håvard; Walderhaug, Ståle; Antonsen, yngve; Ellingsen, May-Britt; Håheim-Saers, Nils; Heggelund, Yngve; Anfinsen, Stian Normann (Research report; Forskningsrapport, 2016-05-03)
      Prosjektets mål er å bidra til økt kunnskap om hvordan etablere delt situasjonsforståelse mellom sentrale aktører innen SAR i Nordområdet. Prosjektgruppa har arbeidet ut ifra en menneske-teknologi-organisasjon (MTO) tilnærming og hvor vi har sett på <br>1) menneskelige og organisatoriske faktorer og <br>2) tekniske faktorer som virker inn på etableringen av delt situasjonsforståelse mellom aktører.<br> ...
    • 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 ...