Artikler, rapporter og annet (fysikk og teknologi): Recent submissions
Now showing items 821-840 of 1057
-
Chirp coded ultrasonic pulses used for scanning acoustic microscopy
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-11-02)In the present study, chirp coded pulses are investigated with respect to high frequency imaging. These pulses were used drive broadband polymer transducers assembled from an adhesive-free layer-be-layer deposition method. The image quality obtained from using a long chirp coded pulse was compared with images generated from shorter pulses. This includes the Ricker wavelet and the square pulse most ... -
Combination of large and small basis sets in electronic structure calculations on large systems
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-04)Two basis sets-a large and a small one-are associated with each nucleus of the system. Each atom has its own separate one-electron basis comprising the large basis set of the atom in question and the small basis sets for the partner atoms in the complex. The perturbed atoms in molecules and solids model is at core of the approach since it allows for the definition of perturbed atoms in a system. It ... -
Subaperture analysis of polarimetric SAR data for iceberg detection
(Konferansebidrag; Conference object, 2016-11-03)This paper is focused on investigations of the improved detection of icebergs in open water using spectral analysis of polarimetric SAR data. The objectives of this study are to analyze the behavior of ice objects in open water using the sublook cross-correlation magnitude (SCM). It is shown that there is an improvement of iceberg-sea contrast when the SCM is used instead of multilook intensities ... -
Cross-Correlation Between Polarization Channels in SAR Imagery Over Oceanographic Features
(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 ... -
Is a net life cycle balance for energy and materials achievable for a zero emission single-family building in Norway?
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-03-01)In this study, the objective is to redesign a previous concept for a single-family Zero greenhouse gas Emission Building (ZEB). The concept is redesigned based on comparing greenhouse gas (GHG) emission loads and compensation from different design solutions applied in Norwegian single-family ZEB pilot buildings and selected sensitivity studies. The objective is to see if a previously developed ZEB ... -
Carbon Nanotube Spectrally Selective Solar Absorbers
(Journal article; Tidsskriftartikkel; Peer reviewed, 2015)The use of multi-walled carbon nanotubes (MWCNTs) as spectrally selective solar thermal absorbers (SSA) in solar thermal collectors is presented in this paper. CNT layers were coated by electrophoretic deposition (EPD) on aluminum substrates. Stable aqueous CNT suspensions consisted of multi-walled CNTs, DI water and surfactant was used for EPD. The deposited samples were heat treated in a tube ... -
Numerical Simulation of Microwave Scattering from Sea Ice Based on The Finite Element Method
(Journal article; Tidsskriftartikkel; Peer reviewed, 2016-11-03)In this paper, a 2-dimensional scattering model for sea ice based on the Finite Element Method (FEM) is presented. The scattering problem is formulated following a physics-separate strategy. The wave in the air domain is expressed by the scattered field formulation, while the wave in the sea ice domain is expressed by the total field formulation. The two separate physics and formulations are coupled ... -
Electrophoretically deposited carbon nanotube spectrally selective solar absorbers
(Journal article; Tidsskriftartikkel; Peer reviewed, 2015-11-11)Three types of carbon nanotubes(CNT) have been investigated regarding their suitability as spectrally selective solar thermal absorbers.The CNT coatings were electrophoretically deposited on aluminum substrates using kinetically stable CNT aqueous suspensions, of which two CNT aqueous suspensions (N-CNT and P-CNT suspensions) were prepared as part of this study and the third one (T-CNT suspension) ... -
A comparative study of sea clutter covariance matrix estimators
(Journal article; Tidsskriftartikkel; Peer reviewed, 2013-10-23)Estimation of the polarimetric covariance matrix is an important task in statistical modeling of sea clutter for maritime applications of polarimetric synthetic aperture radar (PolSAR) data. This work provides a comprehensive study of four covariance matrix estimators: the maximum likelihood estimators under the Gaussian distribution (G-ML) and the K distribution (K-ML), an approximation of the ... -
Level crossings and excess times due to a superposition of uncorrelated exponential pulses
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-01-10)A well-known stochastic model for intermittent fluctuations in physical systems is investigated. The model is given by a superposition of uncorrelated exponential pulses, and the degree of pulse overlap is interpreted as an intermittency parameter. Expressions for excess time statistics, that is, the rate of level crossings above a given threshold and the average time spent above the threshold, are ... -
Oil Spill Dispersion in Full-polarimetric and Hybrid-polarity SAR
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-12-04)We show that indications of spatial dispersion effects on mineral oil slicks are observed by space-borne multipolarization synthetic aperture radar. This is readily perceived by eye when correlating multipolarization synthetic aperture radar observables with the ship track of the dispersion vessel. We investigate real full-polarimetric (linear transmit/linear receive) as well as simulated and real ... -
Intermittent electron density and temperature fluctuations and associated fluxes in the Alcator C-Mod scrape-off layer
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-04-10)The Alcator C-Mod mirror Langmuir probe system has been used to sample data time series of fluctuating plasma parameters in the outboard mid-plane far scrape-off layer. We present a statistical analysis of one second long time series of electron density, temperature, radial electric drift velocity and the corresponding particle and electron heat fluxes. These are sampled during stationary plasma ... -
Improving Doppler frequency estimation from Envisat data
(Journal article; Tidsskriftartikkel; Peer reviewed, 2014-11-06)This paper shows that Envisat ASAR data are degraded by a small periodic variation in gain between internal calibration cycles of the antenna, which introduces a significant bias when we try to estimate line-of-sight surface velocities from the estimated Doppler frequency shifts. We investigate the impact of the gain problems on the derived surface velocity product and propose a simple correction ... -
Subband Extraction Strategies in Ship Detection With the Subaperture Cross-Correlation Magnitude
(Journal article; Tidsskriftartikkel; Peer reviewed, 2012-01-27)The subaperture cross-correlation magnitude (SCM) has previously been proposed as a statistic that improves the contrast between small ship targets and the surrounding sea in synthetic-aperture-radar images. This preprocessing technique utilizes the fast decorrelation of open-water surface ripples on the scale of the SAR wavelength relative to coherent targets such as a ship. However, optimization ... -
Statistical significance of rising and oscillatory trends in global ocean and land temperature in the past 160 years
(Journal article; Tidsskriftartikkel, 2014-03-20)Various interpretations of the notion of a trend in the context of global warming are discussed, contrasting the difference between viewing a trend as the deterministic response to an external forcing and viewing it as a slow variation which can be separated from the background spectral continuum of long-range persistent climate noise. The emphasis in this paper is on the latter notion, and a general ... -
Ice intelligence retrieval by remote sensing - Possibilities and challenges in an operational setting
(Peer reviewed; Chapter; Bokkapittel, 2017)Detecting ice drift velocity when operating offshore in ice-covered waters is crucial during marine operations, as ice actions affect station keeping and ice management. Furthermore, other ice data/intelligence such as ice concentration and thickness are important parameters to determine ice resistance, evaluate performance of icebreakers and predict ice actions on structures. Different sensors are ... -
Probability distribution functions for intermittent scrape-off layer plasma fluctuations
(Journal article; Peer reviewed; Tidsskriftartikkel, 2018-01-24)A stochastic model for intermittent fluctuations in the scrape-off layer of magnetically confined plasmas has been constructed based on a super-position of uncorrelated pulses arriving according to a Poisson process. In the most common applications of the model, the pulse amplitudes are assumed exponentially distributed, supported by conditional averaging of large-amplitude fluctuations in experimental ... -
Magnetotelluric signatures of the complex tertiary fold–thrust belt and extensional fault architecture beneath Brøggerhalvøya, Svalbard
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-12-18)Magnetotelluric (MT) data were recently collected on Brøggerhalvøya, Svalbard, in a 0.003–1000 s period range along a curved WNW–ESE profile. The collected data manifested strong three-dimensional (3D) effects. We modelled the full impedance tensor with tipper and bathymetry included in 3D, and benchmarked the result with determinant data two-dimensional (2D) inversion. The final inversion results ... -
Evaluation of a method to derive ionospheric conductivities using two auroral emissions (428 and 630 nm) measured with a photometer at Tromsø (69.6°N)
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-07-03)This paper mainly aims at evaluating capabilities of derivation of ionospheric conductivities using two principal auroral emissions (427.8 and 630 nm). We have evaluated a photometric method of derivation of ionospheric conductivities based on simultaneous observations of a photometer (feld of view = ~1.2°), a digital camera, and the EISCAT UHF radar (feld of view = ~0.7°) operated at Tromsø, ... -
Classification of low backscatter ocean regions using log-cumulants
(Conference object; Konferansebidrag, 2015-01)In a synthetic aperture radar image, low backscatter regions of various origin can be observed in ocean areas. Operational oil spill detection services work to discriminate anthropogenic oil spills from natural phenomena such as seeps, low wind fields, thin ice and biogenic slicks. In this paper, we investigate the potential of using matrix log-cumulants for this purpose.