Artikler, rapporter og annet (fysikk og teknologi): Nye registreringer
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Multi-frequency polarimetric SAR signatures of lead sea ice and oil spills
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-12-04)Synthetic aperture radar is used to identify and monitor oil spills. Separation from oil spill look-alikes is an important part of a fully automatic oil spill detection scheme. Here we investigate the polarimetric signatures for oil spills and newly formed sea ice (a well-known look-alike) in fully polarimetric Radarsat-2 satellite scenes. Using the fully polarimetric scenes we calculate four different ... -
Multistatic Specular Meteor Radar Network in Peru: System Description and Initial Results
(Journal article; Tidsskriftartikkel; Peer reviewed, 2020-12-10)The mesosphere and lower thermosphere (MLT) region is dominated globally by dynamics at various scales: planetary waves, tides, gravity waves, and stratified turbulence. The latter two can coexist and be significant at horizontal scales less than 500 km, scales that are difficult to measure. This study presents a recently deployed multistatic specular meteor radar system, SIMONe Peru, which can be ... -
Can We Automate Diagrammatic Reasoning?
(Journal article; Tidsskriftartikkel; Peer reviewed, 2020-05-06)Diagrammatic reasoning (DR) problems are well known. However, solving DR problems represented in 4 × 1 Raven’s Progressive Matrix (RPM) form using computer vision and pattern recognition has not yet been tried. Emergence of deep learning techniques aided by advanced computing can be exploited to solve such DR problems. In this paper, we propose a new learning framework by combining LSTM and Convolutional ... -
Video trajectory analysis using unsupervised clustering and multi-criteria ranking
(Journal article; Tidsskriftartikkel; Peer reviewed, 2020-05-13)Surveillance camera usage has increased significantly for visual surveillance. Manual analysis of large video data recorded by cameras may not be feasible on a larger scale. In various applications, deep learning-guided supervised systems are used to track and identify unusual patterns. However, such systems depend on learning which may not be possible. Unsupervised methods relay on suitable features ... -
Horizontal electric fields from flow of auroral O+(2P) ions at sub-second temporal resolution
(Journal article; Tidsskriftartikkel; Peer reviewed, 2020-07-14)Electric fields are a ubiquitous feature of the ionosphere and are intimately linked with aurora through particle precipitation and field-aligned currents. They exhibit order-of-magnitude changes on temporal and spatial scales of seconds and kilometres respectively which are not easy to measure; knowing their true magnitude and temporal variability is important for a theoretical understanding of ... -
Intermittent fluctuations due to Lorentzian pulses in turbulent thermal convection
(Journal article; Tidsskriftartikkel; Peer reviewed, 2020-08-03)Turbulent motions due to flux-driven thermal convection are investigated by numerical simulations and stochastic modeling. Tilting of convection cells leads to the formation of sheared flows and quasi-periodic relaxation oscillations for the energy integrals far from the threshold for linear instability. The probability density function for the temperature and radial velocity fluctuations in the ... -
Blob interactions in 2D scrape-off layer simulations
(Journal article; Tidsskriftartikkel; Peer reviewed, 2020-12-01)Interaction of coherent structures known as blobs in the scrape-off layer of magnetically confined plasmas is investigated. Isolated and interacting seeded blobs, as well as full plasma turbulence, are studied by two-dimensional numerical simulations. The features of the blobs (position, size, amplitude) are determined with a blob tracking algorithm, which identifies them as coherent structures with ... -
Snow and Ice Thickness Retrievals Using GNSS-R: Preliminary Results of the MOSAiC Experiment
(Journal article; Tidsskriftartikkel; Peer reviewed, 2020-12-10)The FSSCat mission was the 2017 ESA Sentinel Small Satellite (S⌃3) Challenge winner and the Copernicus Masters competition overall winner. It was successfully launched on 3 September 2020 onboard the VEGA SSMS PoC (VV16). FSSCat aims to provide coarse and downscaled soil moisture data and over polar regions, sea ice cover, and coarse resolution ice thickness using a combined L-band microwave radiometer ... -
Hyperspectral Nonlinear Unmixing by Using Plug-and-Play Prior for Abundance Maps
(Journal article; Tidsskriftartikkel; Peer reviewed, 2020-12-16)Spectral unmixing (SU) aims at decomposing the mixed pixel into basic components, called endmembers with corresponding abundance fractions. Linear mixing model (LMM) and nonlinear mixing models (NLMMs) are two main classes to solve the SU. This paper proposes a new nonlinear unmixing method base on general bilinear model, which is one of the NLMMs. Since retrieving the endmembers’ abundances represents ... -
Millstone Hill ISR Measurements of Small Aspect Angle Spectra
(Journal article; Tidsskriftartikkel; Peer reviewed, 2020-05-04)The Millstone Hill incoherent scatter (IS) radar is used to measure spectra close to perpendicular to the Earth's magnetic field, and the data are fit to three different forward models to estimate ionospheric temperatures. IS spectra measured close to perpendicular to the magnetic field are heavily influenced by Coulomb collisions, and the temperature estimates are sensitive to the collision operator ... -
Automatic Grading of Retinal Blood Vessel in Deep Retinal Image Diagnosis
(Journal article; Tidsskriftartikkel; Peer reviewed, 2020-09-01)Automatic grading of retinal blood vessels from fundus image can be a useful tool for diagnosis, planning and treatment of eye. Automatic diagnosis of retinal images for early detection of glaucoma, stroke, and blindness is emerging in intelligent health care system. The method primarily depends on various abnormal signs, such as area of hard exudates, area of blood vessels, bifurcation points, ... -
The Structure of Climate Variability Across Scales
(Journal article; Tidsskriftartikkel; Peer reviewed, 2020-03-05)One of the most intriguing facets of the climate system is that it exhibits variability across all temporal and spatial scales; pronounced examples are temperature and precipitation. The structure of this variability, however, is not arbitrary. Over certain spatial and temporal ranges, it can be described by scaling relationships in the form of power laws in probability density distributions and ... -
Person Re-identification in Videos by Analyzing Spatio-temporal Tubes
(Journal article; Tidsskriftartikkel; Peer reviewed, 2020-06-23)Typical person re-identification frameworks search for <i>k</i> best matches in a gallery of images that are often collected in varying conditions. The gallery usually contains image sequences for video re-identification applications. However, such a process is time consuming as video re-identification involves carrying out the matching process multiple times. In this paper, we propose a new method ... -
Capacity and Limits of Multimodal Remote Sensing: Theoretical Aspects and Automatic Information Theory-Based Image Selection
(Journal article; Tidsskriftartikkel; Peer reviewed, 2020-08-17)Although multimodal remote sensing data analysis can strongly improve the characterization of physical phenomena on Earth's surface, nonidealities and estimation imperfections between records and investigation models can limit its actual information extraction ability. In this article, we aim at predicting the maximum information extraction that can be reached when analyzing a given data set. By ... -
A Novel Rayleigh Dynamical Model for Remote Sensing Data Interpretation
(Journal article; Tidsskriftartikkel; Peer reviewed, 2020-02-19)This article introduces the Rayleigh autoregressive moving average (RARMA) model, which is useful to interpret multiple different sets of remotely sensed data, from wind measurements to multitemporal synthetic aperture radar (SAR) sequences. The RARMA model is indeed suitable for continuous, asymmetric, and nonnegative signals observed over time. It describes the mean of Rayleigh-distributed ... -
Comparison of Machine Learning Methods for Predicting Quad-Polarimetric Parameters from Dual-Polarimetric SAR Data
(Journal article; Tidsskriftartikkel; Peer reviewed, 2021-02-17)This paper addresses the problem of up-scaling full polarimetric (quad-pol) parameters from small quad-pol synthetic aperture radar (SAR) scenes to large dual-pol scenes, using a sophisticated Machine Learning (ML) method, namely the Gaussian Process Regression (GPR). The approach is to let the GPR model learn the relationships between the dual-pol input data and the quad-pol parameters on a quad-pol ... -
Rethinking the role of solar energy under location specific constraints
(Journal article; Tidsskriftartikkel; Peer reviewed, 2020-09-22)In this manuscript we evaluate the potential of photovoltaic systems to meet some dedicated energy demand in specific geographic locations. Our approach is based on location-specific constraints rather than on pre-established, location-independent methodologies or assumptions. First, we propose that a thorough analysis of the socio-economic and technical possibilities of a location must act as the ... -
A Possible Explanation of Interhemispheric Asymmetry of Equatorial Plasma Bubbles in Airglow Images
(Journal article; Tidsskriftartikkel; Peer reviewed, 2020-02-28)Equatorial plasma bubbles resulting from equatorial spread urn:x-wiley:jgra:media:jgra55597:jgra55597-math-0002 are well known to be aligned along the Earth's geomagnetic fields. During the geomagnetic storm on 17 March 2015, all‐sky airglow observations from Tirunelveli (8.7°N, 77.8°E, 1.7°N dip latitude) showed an apparent interhemispheric asymmetry in the tilt of the equatorial plasma bubbles. ... -
Integrating Incidence Angle Dependencies Into the Clustering-Based Segmentation of SAR Images
(Journal article; Tidsskriftartikkel; Peer reviewed, 2020-05-28)Synthetic aperture radar systems perform signal acquisition under varying incidence angles and register an implicit intensity decay from near to far range. Owing to the geometrical interaction between microwaves and the imaged targets, the rates at which intensities decay depend on the nature of the targets, thus rendering single-rate image correction approaches only partially successful. The decay, ... -
Necessary Conditions for Warm Inflow Toward the Filchner Ice Shelf, Weddell Sea
(Journal article; Tidsskriftartikkel; Peer reviewed, 2020-11-09)Understanding changes in Antarctic ice shelf basal melting is a major challenge for predicting future sea level. Currently, warm Circumpolar Deep Water surrounding Antarctica has limited access to the Weddell Sea continental shelf; consequently, melt rates at Filchner‐Ronne Ice Shelf are low. However, large‐scale model projections suggest that changes to the Antarctic Slope Front and the coastal ...