Now showing items 1-10 of 389
Dust charging and density conditions deduced from observations of PMWE modulated by artificial electron heating
(Journal article; Tidsskriftartikkel; Peer reviewed, 2011)
We present an analysis of relatively strong Polar Mesospheric Winter Echoes (PMWE) under artificial electron heating that changes the PMWE intensity. A major purpose is to find reliable estimates of the relaxation time of the heater modified PMWE to their undisturbed state during the heater switch-off phase; the implications regarding charge/discharge mechanisms; and to exploit the diagnostic potential ...
A K-Wishart Markov random field model for clustering of polarimetric SAR imagery
(Conference object; Konferansebidrag, 2011)
Capillary suction model as pipes of different sizes: flow conditions and comparison with experiments
(Conference object; Konferansebidrag, 2012)
ABSTRACT Absorption of water in concrete is often described by the simple linear water uptake vs. square-root-of-time law. However, a deviation from this behaviour is frequently seen depending on factors such as initial water content, water/binder ratio and specimen thickness. The deviation increases with thickness (typically from 25 to 100 mm) and is seen even for very dry specimens with ...
Imaging Sea Ice Structure by Remote Sensing Sensors
(Journal article; Tidsskriftartikkel; Peer reviewed, 2015-06-14)
This paper will investigate how new developments in remote sensing and sensor technologies can be applied to image the structure of the sea ice surface. Both segmentation of multipolarimetric synthetic aperture radar images and strategies for the analyses of polarimetric SAR data of sea ice are addressed. The analysis is based on a Radarsat 2 PolSAR scene of from the Fram Strait in September ...
Magnitude of extreme heat waves in present climate and their projection in a warming world
(Journal article; Tidsskriftartikkel; Peer reviewed, 2014)
An extreme heat wave occurred in Russia in the summer of 2010. It had serious impacts on humans and natural ecosystems, it was the strongest recorded globally in recent decades and exceeded in amplitude and spatial extent the previous hottest European summer in 2003. Earlier studies have not succeeded in comparing the magnitude of heat waves across continents and in time. This study introduces a new ...
Linear scaling Coulomb interaction in the multiwavelet basis, a parallel implementation
(Journal article; Tidsskriftartikkel; Peer reviewed, 2014-08-27)
We present a parallel and linear scaling implementation of the calculation of the electrostatic potential arising from an arbitrary charge distribution. Our approach is making use of the multi-resolution basis of multiwavelets. The potential is obtained as the direct solution of the Poisson equation in its Green’s function integral form. In the multiwavelet basis, the formally non local ...
Effect of dynamical friction on interchange motion of plasma filaments
(Journal article; Tidsskriftartikkel; Peer reviewed, 2012)
Mesospheric temperatures and sodium properties measured with the ALOMAR Na lidar compared with WACCM
(Journal article; Tidsskriftartikkel; Peer reviewed, 2015-01-16)
We present a comparison of the temperature and sodium layer properties observed by the ALOMAR Na lidar (69.3°N, 16.0°E) and simulated by the Whole Atmosphere Community Climate Model with specified dynamics and implemented sodium chemistry (WACCM-Na). To constrain the meteorological fields below 60 km, we use MERRA and GEOS-5. For the years 2008 to 2012, we analyse daily averages of temperature ...
Multi-radar observations of polar mesosphere summer echoes during the PHOCUS campaign on 20-22 July 2011
(Journal article; Tidsskriftartikkel; Peer reviewed, 2014-06-27)
During the PHOCUS rocket campaign, on 20-22 July 2011, the observations of polar mesosphere summer echoes (PMSE) were made by three mesosphere-stratosphere-troposphere radars, operating at about 50 MHz. One radar, ESRAD is located at Esrange in Sweden, where the rocket was launched, two other radars, MAARSY and MORRO, are located 250 km north-west and 200 km north of ESRAD, respectively, on the other ...
Statistical Unmixing of SAR Images
(Preprint; Manuskript, 2016-02-03)
A method is presented which uses logarithmic statistics to detect and characterise class mixtures and targets in background clutter in synthetic aperture radar (SAR) images. Mixtures of ground cover types show up as extreme radar texture in statistical analysis of SAR images. Instead of modelling this as a spatially nonstationary radar cross section, this paper demonstrates how a mixture model ...