Recent additions

  • Improving Chlorophyll-a Estimation from Sentinel-2 (MSI) in the Barents Sea using Machine Learning 

    Asim, Muhammad; Brekke, Camilla; Mahmood, Arif; Eltoft, Torbjørn; Reigstad, Marit (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-04-22)
    This article addresses methodologies for remote sensing of ocean Chlorophyll-a (Chl-a), with emphasis on the Barents Sea. We aim at improving the monitoring capacity by integrating in situ Chl-a observations and optical remote sensing to locally train machine learning (ML) models. For this purpose, in situ measurements of Chl-a ranging from 0.014–10.81 mg/m <sup>3</sup> , collected for the years ...
  • Spectral shaping of ring resonator transmission response 

    Yadav, Mukesh; Noh, Jong Wook; Hjelme, Dag Roar; Aksnes, Astrid (Journal article; Tidsskriftartikkel; Peer reviewed, 2021)
    We present a Mach-Zehnder interferometer assisted ring resonator configuration (MARC) to realize resonator transmission spectra with unique spectral signatures and significantly large effective free spectral ranges. Transmission spectra with unique spectral signatures are generated by changing the angular separation between the through port and the drop port waveguides of the ring resonator (RR). ...
  • Radar imaging with EISCAT 3D 

    Stamm, Johann; Vierinen, Juha; Urco, Juan M.; Gustavsson, Björn; Chau, Jorge L. (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-02-04)
    A new incoherent scatter radar called EISCAT 3D is being constructed in northern Scandinavia. It will have the capability to produce volumetric images of ionospheric plasma parameters using aperture synthesis radar imaging. This study uses the current design of EISCAT 3D to explore the theoretical radar imaging performance when imaging electron density in the E region and compares numerical techniques ...
  • Predicting Energy Demand in Semi-Remote Arctic Locations 

    Foldvik Eikeland, Odin; Bianchi, Filippo Maria; Chiesa, Matteo; Apostoleris, Harry; Hansen, Morten; Chiou, Yu-Cheng (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-02-03)
    Forecasting energy demand within a distribution network is essential for developing strategies to manage and optimize available energy resources and the associated infrastructure. In this study, we consider remote communities in the Arctic located at the end of the radial distribution network without alternative energy supply. Therefore, it is crucial to develop an accurate forecasting model to ...
  • A new auroral phenomenon, the anti-black aurora 

    Nel, A.E.; Kosch, M.J.; Keith Whiter, Daniel; Gustavsson, Björn Johan; Aslaksen, Torun Helene (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-01-19)
    Black auroras are small-scale features embedded in the diffuse background aurora, typically occurring post-substorm after magnetic midnight and with an eastward drift imposed. Black auroras show a significant reduction in optical brightness compared to the surrounding diffuse aurora, and can appear as slow-moving arcs or rapidly-moving patches and arc segments. We report, for the first time, an even ...
  • Direct and indirect impacts of climate change on wheat yield in the Indo-Gangetic plain in India 

    Daloz, Anne Sophie; Rydsaa, Johanne Hope; Sillmann, Jana; Hodnebrog, Øivind; Oort, Bob Eric Helmuth van; Emberson, Lisa; Zhang, Tianyi; Agrawal, Madhoolika (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-02-28)
    The Indo-Gangetic Plain (IGP) is one of the main wheat-production regions in India and the world. With climate change, wheat yields in this region will be affected through changes in temperature and precipitation and decreased water availability for irrigation, raising major concerns for national and international food security. Here we use a regional climate model and a crop model to better understand ...
  • Sea Ice Classification of SAR Imagery Based on Convolution Neural Networks 

    Khaleghian, Salman; Ullah, Habib; Kræmer, Thomas; Hughes, Nick; Eltoft, Torbjørn; Marinoni, Andrea (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-04-29)
    We explore new and existing convolutional neural network (CNN) architectures for sea ice classification using Sentinel-1 (S1) synthetic aperture radar (SAR) data by investigating two key challenges: binary sea ice versus open-water classification, and a multi-class sea ice type classification. The analysis of sea ice in SAR images is challenging because of the thermal noise effects and ambiguities ...
  • The Framework for Ice Sheet-Ocean Coupling (FISOC) V1.1 

    Gladstone, Rupert; Galton-Fenzi, Benjamin K.; Gwyther, David; Zhou, Qin; Hattermann, Tore; Zhao, Chen; Jong, Lenneke; Xia, Yuwei; Guo, Xiaoran; Petrakopoulos, Konstantinos; Zwinger, Thomas; Shapero, Daniel; Moore, John C. (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-02-11)
    A number of important questions concern processes at the margins of ice sheets where multiple components of the Earth system, most crucially ice sheets and oceans, interact. Such processes include thermodynamic interaction at the ice–ocean interface, the impact of meltwater on ice shelf cavity circulation, the impact of basal melting of ice shelves on grounded ice dynamics and ocean controls on ...
  • Investigation of Polar Mesospheric Summer Echoes Using Linear Discriminant Analysis 

    Jozwicki, Dorota; Sharma, Puneet; Mann, Ingrid (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-02-02)
    Polar Mesospheric Summer Echoes (PMSE) are distinct radar echoes from the Earth’s upper atmosphere between 80 to 90 km altitude that form in layers typically extending only a few km in altitude and often with a wavy structure. The structure is linked to the formation process, which at present is not yet fully understood. Image analysis of PMSE data can help carry out systematic studies to characterize ...
  • Automatic question generation and answer assessment: a survey 

    Das, Bidyut; Majumder, Mukta; Phadikar, Santanu; Sekh, Arif Ahmed (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-03-18)
    Learning through the internet becomes popular that facilitates learners to learn anything, anytime, anywhere from the web resources. Assessment is most important in any learning system. An assessment system can find the self-learning gaps of learners and improve the progress of learning. The manual question generation takes much time and labor. Therefore, automatic question generation from learning ...
  • Direct and indirect impacts of climate change on wheat yield in the Indo-Gangetic plain in India 

    Daloz, Anne Sophie; Rydsaa, Johanne Hope; Hodnebrog, Øivind; Sillmann, Jana; Oort, Bob Eric Helmuth van; Mohr, Christian Wilhelm; Agrawal, M.; Emberson, L.; Stordal, Frode; Zhang, T. (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-02-28)
    The Indo-Gangetic Plain (IGP) is one of the main wheat-production regions in India and the world. With climate change, wheat yields in this region will be affected through changes in temperature and precipitation and decreased water availability for irrigation, raising major concerns for national and international food security. Here we use a regional climate model and a crop model to better understand ...
  • The Impact of Turbulence on the Ionosphere and Magnetosphere 

    Guio, Patrick; Pécseli, Hans L (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-01-25)
    An important property associated with turbulence in plasmas and fluids is anomalous transport. Plasma, being a good conductor, can in addition be affected by turbulence causing an anomalous resistivity that can significantly exceed its classical counterpart. While turbulent transport may be adequately described in configuration space, some aspects of the anomalous resistivity are best accounted for ...
  • Formation of an additional density peak in the bottom side of the sodium layer associated with the passage of multiple mesospheric frontal systems 

    Narayanan, Viswanathan Lakshmi; Nozawa, Satonori; Oyama, Shin-Ichiro; Mann, Ingrid; Shiokawa, Kazuo; Otsuka, Yuichi; Saito, Norihito; Wada, Satoshi; Kawahara, Takuya D.; Takahashi, Toru (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-02-18)
    We present a detailed investigation of the formation of an additional sodium density peak at altitudes of 79–85 km below the main peak of the sodium layer based on sodium lidar and airglow imager measurements made at Ramfjordmoen near Tromsø, Norway, on the night of 19 December 2014. The airglow imager observations of OH emissions revealed four passing frontal systems that resembled mesospheric ...
  • Deep Image Translation With an Affinity-Based Change Prior for Unsupervised Multimodal Change Detection 

    Luppino, Luigi Tommaso; Kampffmeyer, Michael; Bianchi, Filippo Maria; Moser, Gabriele; Serpico, Sebastiano Bruno; Jenssen, Robert; Anfinsen, Stian Normann (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-02-17)
    Image translation with convolutional neural networks has recently been used as an approach to multimodal change detection. Existing approaches train the networks by exploiting supervised information of the change areas, which, however, is not always available. A main challenge in the unsupervised problem setting is to avoid that change pixels affect the learning of the translation function. We propose ...
  • Two-dimensional TIRF-SIM–traction force microscopy (2D TIRF-SIM-TFM) 

    Barbieri, Liliana; Colin-York, Huw; Korobchevskaya, Kseniya; Li, Di; Wolfson, Deanna; Karedla, Narain; Schneider, Falk; Ahluwalia, Balpreet Singh; Seternes, Tore; Dalmo, Roy Ambli; Dustin, Michael L.; Li, Dong; Fritzsche, Marco (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-04-12)
    Quantifying small, rapidly evolving forces generated by cells is a major challenge for the understanding of biomechanics and mechanobiology in health and disease. Traction force microscopy remains one of the most broadly applied force probing technologies but typically restricts itself to slow events over seconds and micron-scale displacements. Here, we improve >2-fold spatially and >10-fold temporally ...
  • Reducing Objective Function Mismatch in Deep Clustering with the Unsupervised Companion Objective 

    Trosten, Daniel Johansen; Jenssen, Robert; Kampffmeyer, Michael (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-04-19)
    Preservation of local similarity structure is a key challenge in deep clustering. Many recent deep clustering methods therefore use autoencoders to help guide the model's neural network towards an embedding which is more reflective of the input space geometry. However, recent work has shown that autoencoder-based deep clustering models can suffer from objective function mismatch (OFM). In order to ...
  • The influence of surface charge on the coalescence of ice and dust particles in the mesosphere 

    Baptiste, Joshua; Williamsen, Connor; Fox, John; Stace, Anthony, J.; Hassan, Muhammad; Braun, Stefanie; Mann, Ingrid; Besley, Elena (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-06-09)
    Agglomeration of charged ice and dust particles in the mesosphere and lower thermosphere is studied using a classical electrostatic approach, which is extended to capture the induced polarisation of surface charge. Collision outcomes are predicted whilst varying the particle size, charge, dielectric constant, relative kinetic energy, collision geometry and the coefficient of restitution. In addition ...
  • Conjugate ionospheric perturbation during the 2017 solar eclipse 

    Zhang, Shunrong; Erickson, Philip J.; Vierinen, Juha; Aa, Ercha; Rideout, William; Coster, Anthea; Goncharenko, Larisa (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-01-16)
    We report new findings of total electron content (TEC) perturbations in the southern hemisphere at conjugate locations to the northern eclipse on August 21, 2017. We identified a persistent conjugate TEC depletion by 10%–15% during the eclipse time, elongating along magnetic latitudes with at least ∼5° latitudinal width. As the Moon's shadow swept southward, this conjugate depletion moved northward ...
  • Anomalous transport due to large coherent structures in a magnetized toroidal plasma 

    Fredriksen, Åshild; Pécseli, Hans L; Trulsen, Jan Karsten (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-11-18)
    Anomalous transport due to large coherent structures, or coherent events, is studied experimentally in a magnetized toroidal discharge plasma. The present analysis emphasizes anomalous plasma losses as well as transport of electron thermal energy density across magnetic field lines. The experiment was carried out in the Blaamann device at the University of Tromsø. The diagnostics are based on data ...
  • A New Technique for Investigating Dust Charging in the PMSE Source Region 

    Mahmoudian, Alireza; Kosch, Michael J.; Vierinen, Juha; Rietveld, Michael T (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-09-21)
    A new technique for investigating dust charging in the PMSE (polar mesospheric summer echoes) source region is proposed and discussed in this paper. The first high-frequency (HF) modulation of the PMSE with varying pump power was employed during a recent experimental campaign at EISCAT (European Incoherent Scatter Scientific Association). Two experiment setups including HF pump power stepping as ...

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