Recent additions

  • On the relation between polarimetric synthetic aperture radar (SAR) features and sea ice melt pond fraction 

    Fors, Ane Schwenke; Doulgeris, Anthony Paul; Renner, Angelika; Brekke, Camilla; Gerland, Sebastian (Journal article; Tidsskriftartikkel; Peer reviewed, 2015-11-12)
    In this study we examine the relationship between sea ice melt pond fraction and two polarimetric C-band synthetic aperture radar (SAR) features. Three high-resolution SAR scenes were recorded in the Fram Strait in late summer 2011, covering iceberg-fast first-year and old sea ice. In addition, melt pond fraction was retrieved from photographs recorded during a helicopter flight at the study area. ...
  • Mapping sea-ice types from Sentinel-1 considering the surface-type dependent effect of incidence angle 

    Lohse, Johannes; Doulgeris, Anthony Paul; Dierking, Wolfgang (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-06-23)
    Automated classification of sea-ice types in Synthetic Aperture Radar (SAR) imagery is complicated by the class-dependent decrease of backscatter intensity with Incidence Angle (IA). In the log-domain, this decrease is approximately linear over the typical range of space-borne SAR instruments. A global correction does not consider that different surface types show different rates of decrease in ...
  • Ice extent in sub-arctic fjords and coastal areas from 2001 to 2019 analyzed from MODIS imagery 

    O'Sadnick, Megan Eileen; Petrich, Chris; Brekke, Camilla; Skardhamar, Jofrid (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-06-03)
    Results examining variations in the ice extent along the Norwegian coastline based on the analysis of Moderate Resolution Imaging Spectroradiometer (MODIS) images from 2001 to 2019, February through May, are presented. A total of 386 fjords and coastal areas were outlined and grouped into ten regions to assess seasonal and long-term trends in ice extent. In addition, three fjords were examined to ...
  • Added value of multitemporal polarimetric UAVSAR data for permanent scatterers detection 

    Nikaein, Tina; Akbari, Vahid; Arefi, Hossein (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-11-05)
    In the last decades, differential synthetic aperture radar (SAR) interferometric (InSAR) (DInSAR) techniques have been used to estimate the Earth's surface deformation with high resolution. In this paper, we present an approach for increasing the quantity of permanent scattered pixels. These pixels are selected for DInSAR processing based on polarimetric information prepared by new sensors. The ...
  • The impact of system noise in polarimetric SAR imagery on oil spill observations 

    Espeseth, Martine; Brekke, Camilla; Jones, Cathleen Elaine; Holt, Benjamin; Freeman, Anthony (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-01-16)
    The effects of both system additive and multiplicative noise on the X-, C-, and L-band synthetic aperture radar (SAR) data covering oil slicks are examined. Prior studies have attempted to characterize such oil slicks, primarily through analysis of polarimetric SAR data. In this article, we factor in system noise that is added to the backscattered signal, introducing artifacts that can easily be ...
  • Sampling moiré method: a tool for sensing quadratic phase distortion and its correction for accurate quantitative phase microscopy 

    Jayakumar, Nikhil; Ahmad, Azeem; Mehta, Dalip Singh; Ahluwalia, Balpreet Singh (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-03-24)
    The advantages of quantitative phase microscopy (QPM) such as label-free imaging with high spatial sensitivity, live cell compatibility and high-speed imaging makes it viable for various biological applications. The measurement accuracy of QPM strongly relies on the shape of the recorded interferograms, whether straight or curved fringes are recorded during the data acquisition. Moreover, for a ...
  • Automatic fringe pattern enhancement using truly adaptive period-guided bidimensional empirical mode decomposition 

    Gocłowski, Paweł; Trusiak, Maciej; Ahmad, Azeem; Styk, Adam; Mico, Vicente; Ahluwalia, Balpreet Singh; Patorski, Krzysztof (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-02-19)
    Fringe patterns encode the information about the result of a measurement performed via widely used optical full-field testing methods, e.g., interferometry, digital holographic microscopy, moiré techniques, structured illumination etc. Affected by the optical setup, changing environment and the sample itself fringe patterns are often corrupted with substantial noise, strong and uneven background ...
  • Sub-nanometer height sensitivity by phase shifting interference microscopy under environmental fluctuations 

    Ahmad, Azeem; Dubey, Vishesh Kumar; Butola, Ankit; Tinguely, Jean-Claude; Ahluwalia, Balpreet Singh; Mehta, Dalip Singh (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-03-18)
    Phase shifting interferometric (PSI) techniques are among the most sensitive phase measurement methods. Owing to its high sensitivity, any minute phase change caused due to environmental instability results into, inaccurate phase measurement. Consequently, a well calibrated piezo electric transducer (PZT) and highly-stable environment is mandatory for measuring accurate phase map using PSI implementation. ...
  • Measuring Wind Speed Using the Internal Stabilization System of a Quadrotor Drone 

    Simma, Magdalena; Mjøen, Håvard; Boström, Tobias (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-06-16)
    This article proposes a method of measuring wind speed using the data logged by the autopilot of a quadrotor drone. Theoretical equations from works on quadrotor control are utilized and supplemented to form the theoretical framework. Static thrust tests provide the necessary parameters for calculating wind estimates. Flight tests were conducted at a test site with laminar wind conditions with the ...
  • Electron heating by HF pumping of high-latitude ionospheric F-region plasma near magnetic zenith 

    Leyser, Thomas B; Gustavsson, Björn Johan; Rexer, Theresa; Rietveld, Michael T (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-03-06)
    High-frequency electromagnetic pumping of ionospheric F-region plasma at high and mid latitudes gives the strongest plasma response in magnetic zenith, antiparallel to the geomagnetic field in the Northern Hemisphere. This has been observed in optical emissions from the pumped plasma turbulence, electron temperature enhancements, filamentary magnetic field-aligned plasma density irregularities, and ...
  • MusiJ: an ImageJ plugin for video nanoscopy 

    Acuña Maldonado, Sebastian Andres; Ströhl, Florian; Opstad, Ida S.; Ahluwalia, Balpreet S.; Agarwal, Krishna (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-04-14)
    We present an open-source implementation of the fluctuation-based nanoscopy method MUSICAL for ImageJ. This implementation improves the algorithm’s computational efficiency and takes advantage of multi-threading to provide orders of magnitude faster reconstructions than the original MATLAB implementation. In addition, the plugin is capable of generating super-resolution videos from large stacks of ...
  • Ice extent in sub-arctic fjords and coastal areas from 2001 to 2019 analyzed from MODIS imagery 

    O'Sadnick, Megan; Petrich, Christian; Brekke, Camilla; Skarðhamar, Jofrid (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-06-03)
    Results examining variations in the ice extent along the Norwegian coastline based on the analysis of Moderate Resolution Imaging Spectroradiometer (MODIS) images from 2001 to 2019, February through May, are presented. A total of 386 fjords and coastal areas were outlined and grouped into ten regions to assess seasonal and long-term trends in ice extent. In addition, three fjords were examined to ...
  • Exploring the temporal variation of the solar quadrupole moment from relativistic gravitation contributions: A fortuitous circumstance? 

    Rozelot, JP; Eren, Saliha (Journal article; Tidsskriftartikkel; Peer reviewed, 2019-11-08)
    Due to its oblateness, the Sun carries a solar quadrupole moment playing a key role at the crossroad of fundamental solar physics, astrometry and celestial mechanics. There is nowadays a general agreement on its order of magnitude ( ≈2×10-7 ), but its temporal dependence is still poorly known. Helioseismology led to a variation within the solar cycle by less than 0.04%, not yet ...
  • Radio occultation observations of the solar corona over 1.60-1.86R⊙: Faraday rotation and frequency-shift analysis 

    Wexler, David; Hollweg, Joseph V; Efimov, Anatoli I; Song, Paul; Jensen, Elizabeth T; Lionello, Roberto; Vierinen, Juha; Coster, Anthea (Journal article; Tidsskriftartikkel; Peer reviewed, 2019-09-02)
    The study of coronal energy transport, central to the solar wind acceleration problem, relies upon accurate representation of magnetic fields and plasma electron densities. This information is difficult to obtain in middle‐to‐lower coronal regions that may contain complex magnetic structures. Faraday rotation (FR) solar radio occultation observations, which reveal line‐of‐sight (LOS) integrated ...
  • Learning representations of multivariate time series with missing data 

    Bianchi, Filippo Maria; Livi, Lorenzo; Mikalsen, Karl Øyvind; Kampffmeyer, Michael C.; Jenssen, Robert (Journal article; Tidsskriftartikkel; Peer reviewed, 2019-07-19)
    Learning compressed representations of multivariate time series (MTS) facilitates data analysis in the presence of noise and redundant information, and for a large number of variates and time steps. However, classical dimensionality reduction approaches are designed for vectorial data and cannot deal explicitly with missing values. In this work, we propose a novel autoencoder architecture based on ...
  • Automatic generation of fill-in-the-blank question with corpus-based distractors for e-assessment to enhance learning 

    Das, Bidyut; Majumder, Mukta; Phadikar, Santanu; Sekh, Arif Ahmed (Journal article; Tidsskriftartikkel; Peer reviewed, 2019-09-10)
    Knowledge acquisition is the prime objective of a learner from an educational system and evaluating the learner's knowledge is the eventual goal of an examination process. This paper introduces a system which is able to produce fill‐in‐the‐blank questions to test the knowledge of a learner that he or she has accumulated after reading a course material. The question generation task is subdivided into ...
  • A waveguide imaging platform for live-cell TIRF imaging of neurons over large fields of view 

    Opstad, Ida Sundvor; Ströhl, Florian; Fantham, Marcus J.; Hockings, Colin; Vanderpoorten, Oliver; Tartwijk, Francesca W. van; Qiaojin Lin, Julie; Tinguely, Jean-Claude; Dullo, Firehun Tsige; Kaminski‐Schierle, Gabriele S.; Ahluwalia, Balpreet Singh; Kaminski, Clemens F. (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-02-17)
    Large fields of view (FOVs) in total internal reflection fluorescence microscopy (TIRFM) via waveguides have been shown to be highly beneficial for single molecule localisation microscopy on fixed cells [1,2] and have also been demonstrated for short‐term live‐imaging of robust cell types [3‐5], but not yet for delicate primary neurons nor over extended periods of time. Here, we present a waveguide‐based ...
  • Beyond the grid: The promise of solar concentration for non-electrical energy generation 

    Apostoleris, Harry; Chiesa, Matteo (Journal article; Tidsskriftartikkel; Peer reviewed, 2019-09-09)
    As electricity from both photovoltaics and concentrating solar power has become dramatically more affordable in the last several years, the prospect of converting entire national electrical grids to run almost entirely on renewable energy has become feasible in any location with a strong solar resource. However, focusing only on the electric grid neglects the large portion of our energy usage which ...
  • Label-free nanoscopy enabled by coherent imaging with photonic waveguides 

    Ströhl, Florian; Opstad, Ida Sundvor; Tinguely, Jean-Claude; Dullo, Firehun Tsige; Kaminski, Clemens F.; Ahluwalia, Balpreet Singh (Journal article; Tidsskriftartikkel; Peer reviewed, 2019-07-29)
    In this project it was found that Fourier ptychographic microscopy can be improved far beyond its conventional limits via waveguide-based optical systems. Extensive in silico studies showed that images obtained on highrefractive index material waveguide chips in conjunction with hyperspectral illumination light and finely designed waveguide geometries can be combined via a modified phase-retrieval ...
  • Effect on the longitudinal coherence properties of a pseudothermal light source as a function of source size and temporal coherence 

    Ahmad, Azeem; Mahanty, Tanmoy; Dubey, Vishesh; Butola, Ankit; Ahluwalia, Balpreet Singh; Mehta, Dalip Singh (Journal article; Tidsskriftartikkel; Peer reviewed, 2019-04-01)
    In the present Letter, a synthesized pseudothermal light source having high temporal coherence (TC) and low spatial coherence (SC) properties is used. The longitudinal coherence (LC) properties of the spatially extended monochromatic light source are systematically studied. The pseudothermal light source is generated from two different monochromatic laser sources: He–Ne (at 632 nm) and DPSS (at 532 ...

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