Artikler, rapporter og annet (fysikk og teknologi): Recent submissions
Now showing items 341-360 of 947
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Integrated nanophotonic waveguide-based devices for IR and Raman gas spectroscopy
(Journal article; Tidsskriftartikkel; Peer reviewed, 2021-10-30)On-chip devices for absorption spectroscopy and Raman spectroscopy have been developing rapidly in the last few years, triggered by the growing availability of compact and affordable tunable lasers, detectors, and on-chip spectrometers. Material processing that is compatible with mass production has been proven to be capable of long low-loss waveguides of sophisticated designs, which are indispensable ... -
A Multimodal Feature Selection Method for Remote Sensing Data Analysis Based on Double Graph Laplacian Diagonalization
(Journal article; Tidsskriftartikkel; Peer reviewed, 2021-11-13)When dealing with multivariate remotely sensed records collected by multiple sensors, an accurate selection of information at the data, feature, or decision level is instrumental in improving the scenes’ characterization. This will also enhance the system’s efficiency and provide more details on modeling the physical phenomena occurring on the Earth’s surface. In this article, we introduce a flexible ... -
On the applicability of Taylor's hypothesis, including small sampling velocities
(Journal article; Tidsskriftartikkel; Peer reviewed, 2021-12-03)Taylor's hypothesis, or the frozen turbulence approximation, can be used to estimate also the specific energy dissipation rate ϵ by comparing experimental results with the Kolmogorov–Obukhov expression. The hypothesis assumes that a frequency detected by an instrument moving with a constant large velocity <i><b>V</i></b> can be related to a wavenumber by <i><b>ω=kV</i></b>. It is, however, not obvious ... -
Automatic Selection of Relevant Attributes for Multi-Sensor Remote Sensing Analysis: A Case Study on Sea Ice Classification
(Journal article; Tidsskriftartikkel; Peer reviewed, 2021-07-26)It is of considerable benefit to combine information obtained from different satellite sensors to achieve advanced and improved characterization of sea ice conditions. However, it is also true that not all the information is relevant. It may be redundant, corrupted, or unnecessary for the given task, hence decreasing the performance of the algorithms. Therefore, it is crucial to select an optimal ... -
Planetary radar science case for EISCAT 3D
(Journal article; Tidsskriftartikkel; Peer reviewed, 2021-05-12)Ground-based inverse synthetic aperture radar is a tool that can provide insights into the early history and formative processes of planetary bodies in the inner solar system. This information is gathered by measuring the scattering matrix of the target body, providing composite information about the physical structure and chemical makeup of its surface and subsurface down to the penetration ... -
The CPV “toolbox”: New approaches to maximizing solar resource utilization with application-oriented concentrator photovoltaics
(Journal article; Tidsskriftartikkel; Peer reviewed, 2021-02-03)As the scaling of silicon PV cells and module manufacturing has driven solar energy penetration up and costs down, concentrator photovoltaic technologies, originally conceived as a cost-saving measure, have largely been left behind. The loss of market share by CPV is being locked in even as solar energy development encounters significant obstacles related to space constraints in many parts of ... -
Multiresolution Dynamic Mode Decomposition (mrDMD) of Elastic Waves for Damage Localisation in Piezoelectric Ceramic
(Journal article; Tidsskriftartikkel; Peer reviewed, 2021-08-27)The performance of piezoelectric sensors deteriorated due to the presence of defect, delamination, and corrosion that needed to be diagnosed for the effective implementation of the structural health monitoring (SHM) framework. A novel experimental approach based on Coulomb coupling is devised to visualise the interaction of ultrasonic waves with microscale defects in the Lead Zirconate Titanate (PZT). ... -
Monitoring a changing Arctic: Recent advancements in the study of sea ice microbial communities
(Journal article; Tidsskriftartikkel; Peer reviewed, 2021-11-25)Sea ice continues to decline across many regions of the Arctic, with remaining ice becoming increasingly younger and more dynamic. These changes alter the habitats of microbial life that live within the sea ice, which support healthy functioning of the marine ecosystem and provision of resources for human-consumption, in addition to influencing biogeochemical cycles (e.g. air–sea CO2 exchange). With ... -
Surface-based Ku-and Ka-band polarimetric radar for sea ice studies
(Journal article; Tidsskriftartikkel; Peer reviewed, 2020-12-04)To improve our understanding of how snow properties influence sea ice thickness retrievals from presently operational and upcoming satellite radar altimeter missions, as well as to investigate the potential for combining dual frequencies to simultaneously map snow depth and sea ice thickness, a new, surface-based, fully polarimetric Ku- and Ka-band radar (KuKa radar) was built and deployed ... -
A Theoretical Analysis of Deep Neural Networks and Parametric PDEs
(Journal article; Tidsskriftartikkel; Peer reviewed, 2021-06-02)We derive upper bounds on the complexity of ReLU neural networks approximating the solution maps of parametric partial differential equations. In particular, without any knowledge of its concrete shape, we use the inherent low dimensionality of the solution manifold to obtain approximation rates which are significantly superior to those provided by classical neural network approximation results. ... -
Self-Constructing Graph Convolutional Networks for Semantic Labeling
(Journal article; Tidsskriftartikkel; Peer reviewed, 2021-02-17)Graph Neural Networks (GNNs) have received increasing attention in many fields. However, due to the lack of prior graphs, their use for semantic labeling has been limited. Here, we propose a novel architecture called the Self-Constructing Graph (SCG), which makes use of learnable latent variables to generate embeddings and to self-construct the underlying graphs directly from the input features ... -
Multi-View Self-Constructing Graph Convolutional Networks With Adaptive Class Weighting Loss for Semantic Segmentation
(Conference object; Konferansebidrag, 2020-07-28)We propose a novel architecture called the Multi-view Self-Constructing Graph Convolutional Networks (MSCG-Net) for semantic segmentation. Building on the recently proposed Self-Constructing Graph (SCG) module, which makes use of learnable latent variables to self-construct the underlying graphs directly from the input features without relying on manually built prior knowledge graphs, we leverage ... -
Steepening Plasma Density Spectra in the Ionosphere: The Crucial Role Played by a Strong E-Region
(Journal article; Tidsskriftartikkel; Peer reviewed, 2021-07-28)Based on the Swarm 16 Hz Advanced Plasma Density data set, and using the Swarm A satellite, we apply automatic detection of spectral breaks in seven million sampled plasma density power spectra in the high-latitude F-region ionosphere. This way, we survey the presence of plasma irregularity dissipation due to an enhanced E-region conductance, caused both by solar photoionization and particle ... -
Blind Super-Resolution Approach for Exploiting Illumination Variety in Optical-Lattice Illumination Microscopy
(Journal article; Tidsskriftartikkel; Peer reviewed, 2021-08-19)Optical-lattice illumination patterns help in pushing high spatial frequency components of the sample into the optical transfer function of a collection microscope. However, exploiting these high-frequency components require precise knowledge of illumination if reconstruction approaches similar to structured illumination microscopy are employed. Here, we present an alternate blind reconstruction ... -
Year-around C- and L-band observation around the MOSAiC ice floe with high spatial and temporal resolution
(Journal article; Tidsskriftartikkel; Peer reviewed, 2021-10-12)In September 2019, the German research icebreaker Polarstern started the largest multidisciplinary Arctic expedition, the MOSAiC (Multidisciplinary drifting Observatory for the Study of Arctic Climate) drift experiment. Being moored to ice floes at high Arctic for a whole year, thus including the winter season, the main goal of the expedition is to better understand and quantify relevant processes ... -
Observing electric field and neutral wind with EISCAT 3D
(Journal article; Tidsskriftartikkel; Peer reviewed, 2021-11-16)Measurements of height-dependent electric field (E) and neutral wind (u) are important governing parameters of the Earth's upper atmosphere, which can be used to study, for example, how auroral currents close or how energy flows between the ionized and neutral constituents. The new EISCAT 3D (E3D) incoherent scatter radar will be able to measure a three-dimensional ion velocity vector (v) at each ... -
CryoSat-2 Significant Wave Height in Polar Oceans Derived Using a Semi-Analytical Model of Synthetic Aperture Radar 2011–2019
(Journal article; Tidsskriftartikkel; Peer reviewed, 2021-10-18)This paper documents the retrieval of significant ocean surface wave heights in the Arctic Ocean from CryoSat-2 data. We use a semi-analytical model for an idealised synthetic aperture satellite radar or pulse-limited radar altimeter echo power. We develop a processing methodology that specifically considers both the Synthetic Aperture and Pulse Limited modes of the radar that change close to ... -
Single-shot fringe pattern phase retrieval using improved period-guided bidimensional empirical mode decomposition and Hilbert transform
(Journal article; Tidsskriftartikkel; Peer reviewed, 2021-09-17)Fringe pattern analysis is the central aspect of numerous optical measurement methods, e.g., interferometry, fringe projection, digital holography, quantitative phase microscopy. Experimental fringe patterns always contain significant features originating from fluctuating environment, optical system and illumination quality, and the sample itself that severely affect analysis outcome. Before the ... -
A 10-year record of Arctic summer sea ice freeboard from CryoSat-2
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022-10-29)Satellite observations of pan-Arctic sea ice thickness have so far been constrained to winter months. For radar altimeters, conventional methods cannot differentiate leads from meltwater ponds that accumulate at the ice surface in summer months, which is a critical step in the ice thickness calculation. Here, we use over 350 optical and synthetic aperture radar (SAR) images from the summer months ... -
Polar Lows - Moist Baroclinic Cyclones in Four Different Vertical Wind Shear Environments
(Journal article; Tidsskriftartikkel; Peer reviewed, 2021-01-15)Polar lows are intense mesoscale cyclones that develop in polar marine air masses. Motivated by the large variety of their proposed intensification mechanisms, cloud structure, and ambient sub-synoptic environment, we use self-organising maps to classify polar lows. The method is applied to 370 polar lows in the north-eastern Atlantic, which were obtained by matching mesoscale cyclones from ...