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norskBlar i tittel Artikler, rapporter og annet (fysikk og teknologi)
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Object detection neural network improves Fourier ptychography reconstruction
(Journal article; Tidsskriftartikkel; Peer reviewed, 2020-11-23)High resolution microscopy is heavily dependent on superb optical elements and superresolution microscopy even more so. Correcting unavoidable optical aberrations during post-processing is an elegant method to reduce the optical system’s complexity. A prime method that promises superresolution, aberration correction, and quantitative phase imaging is Fourier ptychography. This microscopy technique ... -
Object-based detection of linear kinematic features in sea ice
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-05-18)Inhomogenities in the sea ice motion field cause deformation zones, such as leads, cracks and pressure ridges. Due to their long and often narrow shape, those structures are referred to as Linear Kinematic Features (LKFs). In this paper we specifically address the identification and characterization of variations and discontinuities in the spatial distribution of the total deformation, which ... -
An objective global climatology of polar lows based on reanalysis data
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-04-16)Here we present an objective global climatology of polar lows. In order to obtain objective detection criteria, the efficacy of several parameters for separating polar lows from other cyclones has been compared. The comparison and the climatology are based on the ERA‐Interim reanalysis from 1979 ‐ 2016 and the high‐resolution Arctic System Reanalysis from 2000 ‐ 2012. The most effective parameters ... -
Observation of mesospheric dust and ionospheric conditions during the G-chaser rocket campaign
(Journal article; Tidsskriftartikkel; Peer reviewed, 2019-10)SPID, Smoke Particle Impact Detector, is a Faraday cup detector designed to measure nanometer-sized meteoric smoke particles during rocket flights. We report measurements made with SPID during the G-Chaser student rocket campaign 13 January 2019 and describe the design of the SPID instruments. Model calculations of dust trajectories within the detector result in an effective crosssection of 0.97 for ... -
Observation of mesospheric dust and ionospheric conditions during the G-chaser rocket campaign
(Conference object; Konferansebidrag, 2019)SPID, Smoke Particle Impact Detector, is a Faraday cup detector designed to measure nanometer-sized meteoric smoke particles during rocket flights. We report measurements made with SPID during the G-Chaser student rocket campaign 13 January 2019 and describe the design of the SPID instruments. Model calculations of dust trajectories within the detector result in an effective cross section of 0.97 ... -
Observations of HF-induced instability in the auroral E region
(Journal article; Tidsskriftartikkel; Peer reviewed, 2013)Enhancements were observed in backscattered radar power during an ionospheric heating experiment from two distinct altitude regions in the auroral E region above Tromsø. For the experiment the EISCAT Tromsø heater was operated with O mode and X mode alternated at 4.04 MHz, close to the 3rd electron gyroharmonic. Ion-line data recorded with the EISCAT UHF radar reveal different temporal ... -
Observations of the urban boundary layer in a cold climate city
(Journal article; Tidsskriftartikkel, 2022-11-30)Cold environment supports a large diversity of local climates. Among them, urban climates in northern cities stand out for their pronounced warm temperature anomaly known as the Urban Heat Island (UHI). UHI in northern cities has been already studies through satellite images and in-situ observations in the urban canopy layer (UCL). Yet, the vertical structure of the urban atmospheric boundary layer ... -
Observations of thermospheric neutral winds within the polar cusp and the auroral oval using a Doppler imaging system (DIS).
(Journal article; Tidsskriftartikkel, 1998)Two Doppler imaging systems (DIS) or wide-field imaging Fabry-Perot interferometers (FPI), have recently been commissioned, one at the Auroral Station, Adventdalen, Longyearbyen, Svalbard, and the second at the IRF, Kiruna, Sweden. These instruments can provide wide-field (600 * 800 km) images of neutral wind flows in the upper thermosphere, by measuring the Doppler shift of the atomic oxygen forbidden ... -
Observatoriet i 80-årene
(Journal article; Tidsskriftartikkel, 1980)På terskelen til en ny dekade er det naturlig å stille spørsmålet hva Observatoriets fremtidige rolle skal bli. Vil det fortsatt være behov for forskningsinnsats på Observatoriets tradisjonelle fagfelter, eller skal innsatsen etter hvert anta en annen retning? Vi skal forsøke å belyse dette ved først å rette blikket bakover for derigjennom å få øye på de store utviklingslinjer i den internasjonale ... -
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 ... -
Observing Mesospheric Turbulence With Specular Meteor Radars: A Novel Method for Estimating Second-Order Statistics of Wind Velocity
(Journal article; Peer reviewed, 2019-07)There are few observational techniques for measuring the distribution of kinetic energy within the mesosphere with a wide range of spatial and temporal scales. <br>This study describes a method for estimating the three‐dimensional mesospheric wind field correlation function from specular meteor trail echoes. Each radar echo provides a measurement of a one‐dimensional projection of the wind velocity ... -
Observing Oil Releases from Platforms Using Synthetic Aperture Radar
(Conference object; Konferansebidrag, 2018)Synthetic aperture radar (SAR) is used for operational surveillance of ocean areas and oil spill detection. Oil spills are frequently detected around oil platforms due to the releases of so-called produced water (PW), which is water containing low concentrations of oil that can form surface slicks similar to other oil spills. PW releases are legal within given limits. Understanding the signatures ... -
Ocean Applications
(Chapter; Bokkapittel, 2021-05-11)In this chapter, the most promising techniques to observe oil slicks and to detect metallic targets at sea using polarimetric synthetic aperture radar (SAR) data are reviewed and critically analysed. The detection of oil slicks in SAR data is made difficult not only by the presence of speckle but also by the presence of, e.g. biogenic films, low-wind areas, rain cells, currents, etc., which increase ... -
Oil spill characterization in the hybrid-polarity SAR domain using log-cumulants
(Peer reviewed; Journal article; Tidsskriftsartikkel, 2016-10-18)Log-cumulants have proven to be an interesting tool for evaluating the statistical properties of potential oil spills in polarimetric Synthetic Aperture Radar (SAR) data within the common horizontal (H) and vertical (V) polarization basis. The use of first, second, and third order sample log-cumulants has shown potential for evaluating the texture and the statistical distributions, as well as ... -
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 ... -
Oil-Spill-Response-Oriented Information Products Derived From a Rapid-Repeat Time Series of SAR Images
(Journal article; Tidsskriftartikkel; Peer reviewed, 2020-06-19)New quantitative and semiautomated methods for analyzing oil slick evolution using a time series of L-band synthetic aperture radar (SAR) images with short repeat time are developed and explored. In this study, two methods that are complementary in terms of identifying temporal changes within an oil slick are presented. The two methods reflect two ways of evaluating the oil slicks. The first method ... -
On confinement and plasma acceleration from a small ECR plasma source
(Conference object; Konferansebidrag, 2019)<p>Electron Cyclotron Resonance (ECR) is a technique to create high density, low temperature plasmas that do not depend on a cathode, like arc discharges and are therefore easier to maintain and have a longer lifespan. The use of the Electron Cyclotron Resonance (ECR) for electron heating for Magnetic Nozzle (MN) thrusters have recently received increased interest, as they have been shown to provide ... -
On Importance of Off-Diagonal Elements in the Polarimetric Covariance Matrix: A Sea Ice Application Perspective
(Conference object; Konferansebidrag, 2023-06) -
On Measures of Uncertainty in Classification
(Journal article; Tidsskriftartikkel; Peer reviewed, 2023-10-12)Uncertainty is unavoidable in classification tasks and might originate from data (e.g., due to noise or wrong labeling), or the model (e.g., due to erroneous assumptions, etc). Providing an assessment of uncertainty associated with each outcome is of paramount importance in assessing the reliability of classification algorithms, especially on unseen data. In this work, we propose two measures of ... -
On mechanisms for high-frequency pump-enhanced optical emissions at 557.7 and 630.0gnm from atomic oxygen in the high-latitude F-region ionosphere
(Journal article; Tidsskriftartikkel; Peer reviewed, 2023-12-13)The EISCAT (European Incoherent Scatter Scientific Association) Heating facility was used to transmit powerful high-frequency (HF) electromagnetic waves into the Fregion ionosphere to enhance optical emissions at 557.7 and 630.0 nm from atomic oxygen. The emissions were imaged by several stations of ALIS (Auroral Large Imaging System) in northern Sweden, and the EISCAT UHF incoherent scatter radar ...
