Artikler, rapporter og annet (fysikk og teknologi): Recent submissions
Now showing items 541-560 of 947
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Developing a New Machine-Learning Algorithm for Estimating Chlorophyll-a Concentration in Optically Complex Waters: A Case Study for High Northern Latitude Waters by Using Sentinel 3 OLCI
(Journal article; Tidsskriftartikkel; Peer reviewed, 2019-09-04)The monitoring of Chlorophyll-a (Chl-a) concentration in high northern latitude waters has been receiving increased focus due to the rapid environmental changes in the sub-Arctic, Arctic. Spaceborne optical instruments allow the continuous monitoring of the occurrence, distribution, and amount of Chl-a. In recent years, the Ocean and Land Color Instruments (OLCI) onboard the Sentinel 3 (S3) A and B ... -
Assessment of the RISAT-1 FRS-2 Mode for Oil Spill Observation
(Peer reviewed; Chapter, 2017-12-04)Synthetic aperture radar data acquired by the Radar Imaging Satellite (RISAT-1) over experimental oil spills is here investigated. One quad-polarization scene in the Fine Resolution Alternate Polarization Stripmap (FRS-2) mode is analyzed to evaluate the potential of using this mode for oil spill observation.<br> Oil slicks of varying type and age are clearly detected in the HH and VV channels, with ... -
Dust observations with antenna measurements and its prospects for observations with Parker Solar Probe and Solar Orbiter
(Journal article; Tidsskriftartikkel; Peer reviewed, 2019-12-10)The electric and magnetic field instrument suite FIELDS on board the NASA Parker Solar Probe and the radio and plasma waves instrument RPW on the ESA Solar Orbiter mission that explore the inner heliosphere are sensitive to signals generated by dust impacts. Dust impacts have been observed using electric field antennas on spacecraft since the 1980s and the method was recently used with a number of ... -
Understanding Cassini RPWS Antenna Signals Triggered by Dust Impacts
(Journal article; Tidsskriftartikkel; Peer reviewed, 2019-09-04)Electric field antennas are capable of detecting dust impacts in different space environment. We analyze the dust impact signals detected by the Cassini Radio and Plasma Wave Science instrument at different locations around Saturn and compare them with dust impact signals simulated in laboratory conditions and numerically. The spacecraft potential, the size, and capacitance of the impacted element ... -
Four dimensional quantification of Kelvin-Helmholtz instabilities in the polar summer mesosphere using volumetric radar imaging
(Journal article; Tidsskriftartikkel; Peer reviewed, 2019-12-13)We present and characterize in time and three spatial dimensions a Kelvin‐Helmholtz Instability (KHI) event from polar mesospheric summer echoes (PMSE) observed with the Middle Atmosphere Alomar Radar System. We use a newly developed radar imaging mode, which observed PMSE intensity and line of sight velocity with high temporal and angular resolution. The identified KHI event occurs in a narrow layer ... -
Cosmic noise absorption during solar proton events in WACCM-D and riometer observations
(Journal article; Tidsskriftartikkel; Peer reviewed, 2019-01-18)Solar proton events (SPEs) cause large‐scale ionization in the middle atmosphere leading to ozone loss and changes in the energy budget of the middle atmosphere. The accurate implementation of SPEs and other particle ionization sources in climate models is necessary to understand the role of energetic particle precipitation in climate variability. We use riometer observations from 16 riometer stations ... -
Power-law scaling of uncorrelated plasma bursts
(Conference object; Konferansebidrag, 2019-07) -
Synthetic Aperture Radar Remote Sensing of Operational Platform Produced Water Releases
(Journal article; Tidsskriftartikkel; Peer reviewed, 2019-12-03)Oil spill detection services based on satellite synthetic aperture radar (SAR) frequently detect oil slicks close to platforms due to legal releases of produced water. Separating these slicks from larger releases, e.g., due to accidental leakage is challenging. The aim of this work is to investigate the SAR characteristics of produced water, including the typical appearance in HH/VV data, possible ... -
Separation and characterisation of mineral oil slicks and newly formed sea ice in L-band synthetic aperture radar
(Journal article; Tidsskriftartikkel; Peer reviewed, 2019-11-14)Maritime activities in the Arctic Ocean is increasing and consequently the risk for an oil spill there is rising. Synthetic Aperture Radar (SAR) is used operationally to detect and monitor oil slicks and for sea ice monitoring and observations. Leads are often used for ship routing and within the leads newly formed sea ice is often present. Separation between the low backscatter areas that constitutes ... -
Towards operational sea ice type retrieval using L-band Synthetic aperture radar
(Journal article; Tidsskriftartikkel; Peer reviewed, 2019-11-14)Operational ice services around the world have recognized the economic and environmental benefits that come from the increased capabilities and uses of space-borne Synthetic Aperture Radar (SAR) observation system. The two major objectives in SAR based remote sensing of sea ice is on the one hand to have a large areal coverage, and on the other hand to obtain a radar response that carries as much ... -
The Impact of Additive Noise on Polarimetric RADARSAT-2 Data Covering Oil Slicks
(Journal article; Tidsskriftartikkel; Peer reviewed, 2019-11-14)We attempt to understand how a set of well known polari-metric Synthetic Aperture Radar (SAR) features are impacted by the additive system noise for mineral oil and produced water slicks. For this, we use quad-polarimetric SAR scenes from Radarsat-2. Oil slicks at sea can be detected using SAR instruments, and the dual- (HH-VV) and quad-polarimetric modes can provide additional information about the ... -
Measurement of inner wall limiter SOL widths in KSTAR tokamak
(Journal article; Tidsskriftartikkel; Peer reviewed, 2016-12-27)Scrape-off layer (SOL) widths <i>λ<sub>q</sub></i> are presented from the KSTAR tokamak using fast reciprocating Langmuir probe assembly (FRLPA) measurements at the outboard mid-plane (OMP) and the infra-Red (IR) thermography at inboard limiter tiles in moderately elongated (<i>κ</i> = 1.45 – 1.55) L-mode inner wall-limited (IWL) plasmas under experimental conditions such as B<sub>T</sub> = 2.0 T, ... -
SOL width and intermittent fluctuations in KSTAR
(Journal article; Tidsskriftartikkel; Peer reviewed, 2016-12-27)Radial profiles of the ion saturation current and its fluctuation statistics are presented from probe measurements in L-mode, neutral beam heated plasmas at the outboard mid-plane region of KSTAR. The results are consistent with the familiar two-layer structure, seen elsewhere in tokamak L-mode discharges, with a steep near-SOL profile and a broad far-SOL profile. The profile scale length in the ... -
One-Year Analysis of Dust Impact-Like Events Onto the MMS Spacecraft
(Journal article; Tidsskriftartikkel; Peer reviewed, 2019-10-16)We present an analysis of 1‐year data of dust impacts observed on two of the Earth‐orbiting Magnetospheric Multiscale mission (MMS) spacecraft. The dust impact signals were identified in observations of the electric field probes and were registered simultaneously by monopole and dipole configurations of the instrument. This unique setup allows us to reliably identify changes in the spacecraft potential ... -
Winter storms accelerate the demise of sea ice in the Atlantic sector of the Arctic Ocean
(Journal article; Peer reviewed, 2019-06-25)A large retreat of sea-ice in the ‘stormy’ Atlantic Sector of the Arctic Ocean has become evident through a series of record minima for the winter maximum sea-ice extent since 2015. Results from the Norwegian young sea ICE (N-ICE2015) expedition, a five-month-long (Jan-Jun) drifting ice station in first and second year pack-ice north of Svalbard, showcase how sea-ice in this region is frequently ... -
Authenticating the presence of a relativistic massive black hole binary in OJ 287 using its general relativity centenary flare: Improved orbital parameters
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-10-05)Results from regular monitoring of relativistic compact binaries like PSR 1913+16 are consistent with the dominant (quadrupole) order emission of gravitational waves (GWs). We show that observations associated with the binary black hole (BBH) central engine of blazar OJ 287 demand the inclusion of gravitational radiation reaction effects beyond the quadrupolar order. It turns out that even the effects ... -
Shock location and CME 3D reconstruction of a solar type II radio burst with LOFAR
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-07-19)<p><i>Context - </i>Type II radio bursts are evidence of shocks in the solar atmosphere and inner heliosphere that emit radio waves ranging from sub-meter to kilometer lengths. These shocks may be associated with coronal mass ejections (CMEs) and reach speeds higher than the local magnetosonic speed. Radio imaging of decameter wavelengths (20–90 MHz) is now possible with the Low Frequency Array ... -
Classification of Micro-Damage in Piezoelectric Ceramics Using Machine Learning of Ultrasound Signals
(Journal article; Peer reviewed, 2019-09-28)Ultrasound based structural health monitoring of piezoelectric material is challenging if a damage changes at a microscale over time. Classifying geometrically similar damages with a difference in diameter as small as 100 m is difficult using conventional sensing and signal analysis approaches. Here, we use an unconventional ultrasound sensing approach that collects information of the entire ... -
Multi-scale measurements of mesospheric aerosols and electrons during the MAXIDUSTY campaign
(Journal article; Peer reviewed, 2019-04-08)We present in situ measurements of small-scale fluctuations in aerosol populations as recorded through a mesospheric cloud system from the Faraday cups DUSTY and MUDD during on the MAXIDUSTY-1 and 1B sounding rocket payloads launched in the summer of 2016. <br>Two mechanically identical DUSTY probes mounted with an inter-spacing of ∼10 cm recorded very different currents, with strong spin modulation, ... -
Gaussian Process Sensitivity Analysis for Oceanic Chlorophyll Estimation
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-01-04)Gaussian process regression (GPR) has experienced tremendous success in biophysical parameter retrieval in the past years. The GPR provides a full posterior predictive distribution so one can derive mean and variance predictive estimates, i.e., point-wise predictions and associated confidence intervals. GPR typically uses translation invariant covariances that make the prediction function very ...