147 research outputs found
Time-Dependent Electron Transport I: Modelling of Supra-Thermal Electron Bursts Modulated at 5–10 Hz With Implications for Flickering Aurora
A time-dependent multi-stream electron transport model, AURORA, has been developed for studies of auroral emission-rates during precipitation with large variations on sub-second time-scales. The transport-code accurately takes time-of-flight, energy degradation, scattering and production of secondary electrons into account. AURORA produces ionospheric electron-flux as a function of energy, altitude, time and pitch-angle, with a time-resolution of 3.33 ms. AURORA has been used to simulate flickering aurora by modulating field-aligned bursts (FAB) of electrons modulated at frequencies between 5 and 10 Hz. Intensity modulations of auroral emissions at 4,278, 6,730, 7,444, and 8,446 Å have been calculated, time-shifts on the order of 10 ms between the maxima of the emissions were found
Simulation of high energy tail of electron distribution function
This report presents Monte Carlo simulations of the electron energy distribution for alow ionized plasma interacting with the F-region neutral gas. The results show a depletion in theelectron distribution above 2 eV between 10 and 80 %, decreasing with altitude. The depletion ismainly due to electron energy loss to . This micro-physical energy transfer model gives goodagreement with optical observations of enhanced emissions from at 6300Å and EISCATUHF measurements of electron cooling during HF radio wave heating experiments. Someimplications for incoherent scatter spectra are derived. The results suggest that a weak(approximately 1000 times weaker than the ion-line) and wide (2 MHz) peak around +-1 MHz fromthe ion-line in the EISCAT VHF incoherent scatter spectrum should be a consequence of theelectron-neutral interaction
A technique for volumetric incoherent scatter radar analysis
Volumetric measurements of the ionosphere are important for investigating spatial variations of ionospheric features, like auroral arcs and energy deposition in the ionosphere. In addition, such measurements make it possible to distinguish between variations in space and time. While spatial variations in scalar quantities such as electron density or temperature have been investigated with incoherent scatter radar (ISR) before, spatial variation in the ion velocity, which is a vector quantity, has been hard to measure. The upcoming EISCAT3D radar will be able to do volumetric measurements of ion velocity regularly for the first time. In this paper, we present a technique for relating volumetric measurements of ion velocity to neutral wind and electric field. To regularize the estimates, we use Maxwell's equations and fluid-dynamic constraints. The study shows that accurate volumetric estimates of electric field can be achieved. Electric fields can be resolved at altitudes above 120 km, which is the altitude range where auroral current closure occurs. Neutral wind can be resolved at altitudes below 120 km.</p
Lightboard – a new teaching tool at the Faculty of Science and Technology at UiT
We would like to present a new tool that was built by three lecturers at UiT last
semester – Lightboard. This tool was used before in other countries and other universities, but
never at UiT. The COVID-19 pandemic situation motivated the lecturers to find a way to do online
lectures differently. Blackboard and chalk work well for natural sciences as long as the lecture is
physical and the teacher has an eye contact with the students, but this was not an option since all
lectures were turned to online. The solution was found. The Lightboard gives an opportunity to
face towards the students while recording the lectures and they can follow the lecturer’s hands
while writing
Planetary radar science case for EISCAT 3D
Ground-based inverse synthetic aperture radar is
a tool that can provide insights into the early history and
formative processes of planetary bodies in the inner solar
system. This information is gathered by measuring the scattering matrix of the target body, providing composite information about the physical structure and chemical makeup
of its surface and subsurface down to the penetration depth
of the radio wave. This work describes the technical capabilities of the upcoming 233 MHz European Incoherent
Scatter Scientific Association (EISCAT) 3D radar facility
for measuring planetary surfaces. Estimates of the achievable signal-to-noise ratios for terrestrial target bodies are
provided. While Venus and Mars can possibly be detected,
only the Moon is found to have sufficient signal-to-noise ratio to allow high-resolution mapping to be performed. The
performance of the EISCAT 3D antenna layout is evaluated
for interferometric range–Doppler disambiguation, and it is
found to be well suited for this task, providing up to 20 dB
of separation between Doppler northern and southern hemispheres in our case study. The low frequency used by EISCAT 3D is more affected by the ionosphere than higherfrequency radars. The magnitude of the Doppler broadening
due to ionospheric propagation effects associated with traveling ionospheric disturbances has been estimated. The effect
is found to be significant but not severe enough to prevent
high-resolution imaging. A survey of lunar observing opportunities between 2022 and 2040 is evaluated by investigating
the path of the sub-radar point when the Moon is above the
local radar horizon. During this time, a good variety of look
directions and Doppler equator directions are found, with observations opportunities available for approximately 10 d every lunar month. EISCAT 3D will be able to provide new,
high-quality polarimetric scattering maps of the nearside of
the Moon with the previously unused wavelength of 1.3 m,
which provides a good compromise between radio wave penetration depth and Doppler resolution
Timing Analysis of Parallel Software Using Abstract Execution
Abstract. A major trend in computer architecture is multi-core processors. To fully exploit this type of parallel processor chip, programs running on it will have to be parallel as well. This means that even hard real-time embedded systems will be parallel. Therefore, it is of utmost importance that methods to analyze the timing properties of parallel real-time systems are developed. This paper presents an algorithm that is founded on abstract interpretation and derives safe approximations of the execution times of parallel programs. The algorithm is formulated and proven correct for a simple parallel language with parallel threads, shared memory and synchronization via locks
Manx Arrays: Perfect Non-Redundant Interferometric Geometries
Interferometry applications (e.g., radio astronomy) often wish to optimize the placement of the interferometric elements. One such optimal criterion is a uniform distribution of non-redundant element spacings (in both distance and position angle). While large systems, with many elements, can rely on saturating the sample space, and disregard “wasted” sampling, small arrays with only a few elements are more critical, where a single element can represent a significant fraction of the overall cost. This paper defines a “perfect array” as a mathematical construct having uniform and complete element spacings within a circle of radius equal to the maximum element spacing. Additionally, the largest perfect non-redundant array, comprising six elements, is presented. The geometry is described, along with the properties of the layout and situations where it would be of significant benefit to array application and non-redundant masking designs.</p
Interferometric Imaging with EISCAT_3D for Fine-Scale In-Beam Incoherent Scatter Spectra Measurements
The 233 MHz EISCAT_3D radar system currently under construction in northern Fennoscandia will be able to resolve ionospheric structures smaller than the transmit beam dimensions through the use of interferometric imaging. This capability is made possible by the modular design and digitization of the 119 91-antenna panels located at the main Skibotn site. The main array consists of a cluster of 109 panels, with 10 outlier panels producing unique interferometry baselines. In the present study synthesized incoherent scatter radar signal measurements are used for interferometric imaging analysis with the EISCAT_3D system. The Geospace Environment Model of Ion-Neutral Interactions (GEMINI) model is used to simulate a Kelvin-Helmholtz instability in the cusp region at 50 m resolution to obtain plasma parameters which are then used to generate the synthetic data. The ionospheric data is forward propagated to the EISCAT_3D array, noise is added to the synthetic data, and then an inversion of the data is performed to reconstruct the incoherent scatter spectra at relatively fine scales. By using Singular Value Decomposition (SVD) with Tikhonov regularization it is possible to pre-calculate the inversion matrix for a given range and look direction, with the regularization value scaled based on the SNR. The pre-calculation of the inversion matrix can reduce computational overhead in the imaging solution. This study provides a framework for data processing of ion-line incoherent scatter radar spectra to be imaged on fine-scales. Furthermore, with more development it can be used to test experimental set-ups and to design experiments for EISCAT_3D by investigating the needed integration time for various signal-to-noise ratios, beam patterns and ionospheric conditions
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