221 research outputs found
The Case for Combining a Large Low-Band Very High Frequency Transmitter With Multiple Receiving Arrays for Geospace Research: A Geospace Radar
We argue that combining a highâpower, largeâaperture radar transmitter with several largeâaperture receiving arrays to make a geospace radarâa radar capable of probing nearâEarth space from the upper troposphere through to the solar coronaâwould transform geospace research. We review the emergence of incoherent scatter radar in the 1960s as an agent that unified early, pioneering research in geospace in a common theoretical, experimental, and instrumental framework, and we suggest that a geospace radar would have a similar effect on future developments in space weather research. We then discuss recent developments in radioâarray technology that could be exploited in the development of a geospace radar with new or substantially improved capabilities compared to the radars in use presently. A number of applications for a geospace radar with the new and improved capabilities are reviewed including studies of meteor echoes, mesospheric and stratospheric turbulence, ionospheric flows, plasmaspheric and ionospheric irregularities, and reflection from the solar corona and coronal mass ejections. We conclude with a summary of technical requirements
Statistical framework for estimating GNSS bias
We present a statistical framework for estimating global navigation satellite
system (GNSS) non-ionospheric differential time delay bias. The biases are
estimated by examining differences of measured line integrated electron
densities (TEC) that are scaled to equivalent vertical integrated densities.
The spatio-temporal variability, instrumentation dependent errors, and errors
due to inaccurate ionospheric altitude profile assumptions are modeled as
structure functions. These structure functions determine how the TEC
differences are weighted in the linear least-squares minimization procedure,
which is used to produce the bias estimates. A method for automatic detection
and removal of outlier measurements that do not fit into a model of receiver
bias is also described. The same statistical framework can be used for a single
receiver station, but it also scales to a large global network of receivers. In
addition to the Global Positioning System (GPS), the method is also applicable
to other dual frequency GNSS systems, such as GLONASS (Globalnaya
Navigazionnaya Sputnikovaya Sistema). The use of the framework is demonstrated
in practice through several examples. A specific implementation of the methods
presented here are used to compute GPS receiver biases for measurements in the
MIT Haystack Madrigal distributed database system. Results of the new algorithm
are compared with the current MIT Haystack Observatory MAPGPS bias
determination algorithm. The new method is found to produce estimates of
receiver bias that have reduced day-to-day variability and more consistent
coincident vertical TEC values.Comment: 18 pages, 5 figures, submitted to AM
Polyphase alternating codes
This work introduces a method for constructing polyphase alternating codes in
which the length of a code transmission cycle can be or , where
is a prime number and is a positive integer. The relevant properties
leading to the construction alternating codes and the algorithm for generating
alternating codes is described. Examples of all practical and some not that
practical polyphase code lengths are given.Comment: Submitted to Annales Geophysica
Investigation of exceptionally radar-dark regions on the lunar nearside
Presentation at the 19th International EISCAT Symposium 2019 and 46th Annual European Meeting on Atmospheric Studies by Optical Methods, Oulu, Finland, 19.08. - 23.08.19, arranged by the University of Oulu. (http://www.sgo.fi/Events/EISCAT46AM/). Remote sensing of planetary surfaces is an effective method for gaining knowledge of the processes that
shape the planetary bodies in our solar system. This is useful for uncovering the environment of the primordial solar system and to study the current state of the upper crusts of the other planets in our neighborhood. A recent 6-meter wavelength polarimetric radar map of the Moon [?] showed unexpectedly
low depolarized radar returns in two regions on the lunar nearside. These two areas were a highland region between Mare Imbrium and Mare Frigoris, and the highland area surrounding the Schiller-Zucchius
impact basin. These two regions showed characteristics unlike those of typical highland regions of the
lunar surface. So far, there has been no readily available explanation for this observation. In this study,
it is shown that the likely cause is an increased loss tangent due to chemical differences in the first few
hundred meters of the lunar soil. We also show the absence of any coherent subsurface, which could be
the preserved remains of an ancient basaltic plain. We do this by comparing the 6-meter polarimetric
radar map to other relevant data sets: 1) surface TiO2 and FeO abundance, 2) surface rock population,
3) radar maps of the Moon with other wavelengths, and 4) visual spectrum images of the Moon. The
area near the Schiller-Zucchius basin was shown to be consistent with other areas with similar surface
chemical compositions, but the region between Mare Imbrium and Mare Frigoris showed significantly
lower mean power in comparison to otherwise similar regions. While we can not conclusively determine the cause, we hypothesize that the low radar return is explained by an increased concentration of
iron and titanium oxides in the volume beneath the surface, potentially due to remnants of primordial
lunar volcanism. The results show that long wavelength polarimetric radar measurements of the Moon
are very powerful tools for studying the earliest stages of the evolution of the Moon. The new EISCAT
3D installation will enable new measurements in a wavelength which has not been used before. The
facility can also track the Moon to obtain a long observation time, increasing resolution. The multiple receiving locations will provide excellent interferometric baselines to, among other things, resolve
the range-Doppler ambiguity. Polarimetric measurements are useful for separating surface and volume
scattering, as well as potential target-based decomposition modelling
GPGPU Acceleration of Incoherent Scatter Radar Plasma Line Analysis
The incoherent scatter radar (ISR) technique is a powerful remote sensing
tool for ionosphere and thermosphere dynamics in the near-Earth space
environment. Weak ISR scatter from naturally occurring Langmuir oscillations,
or plasma lines, contain high precision information on the altitude-dependent
thermal ionospheric electron density. However, analyzing this
frequency-dependent scatter over a large number of radar ranges requires large
computational power, especially when the goal is realtime analysis. General
purpose computing on graphics processing units (GPGPU) offers immense
computational speedup when compared to traditional central processing unit
(CPU) calculations for highly parallelizable tasks, and it is well suited for
ISR analysis applications. This paper extends a single graphics processing unit
(GPU) algorithmic solution in a GPGPU framework, and discusses the algorithm
developed, including GPU hardware considerations. Results indicate an
order-of-magnitude improvement over CPU analysis and suggest that GPGPU can
achieve realtime speed for plasma line applications.Comment: 8 pages, 1 figure, 1 table, submitting to Radio Scienc
A New Technique for Investigating Dust Charging in the PMSE Source Region
A new technique for investigating dust charging in the PMSE (polar mesospheric summer echoes) source region is proposed and discussed in this paper. The first high-frequency (HF) modulation of the PMSE with varying pump power was employed during a recent experimental campaign at EISCAT (European Incoherent Scatter Scientific Association). Two experiment setups including HF pump power stepping as well as quasi-continuous power sweeping were used. The experiment was designed based on a computational model capable of simulation of PMSE evolution during HF pump modulation in order to develop a new approach for studying the dust charging process in the PMSE source region. The charge state of dust particles along with background dusty plasma parameters is estimated using the experimental and computational results. A detailed future experimental design based on background dusty-plasma parameters is proposed. Š2020. American Geophysical Union. All Rights Reserved
Phase-coded pulse aperiodic transmitter coding
Both ionospheric and weather radar communities have already adopted the method of transmitting radar pulses in an aperiodic manner when measuring moderately overspread targets. Among the users of the ionospheric radars, this method is called Aperiodic Transmitter Coding (ATC), whereas the weather radar users have adopted the term Simultaneous Multiple Pulse-Repetition Frequency (SMPRF). When probing the ionosphere at the carrier frequencies of the EISCAT Incoherent Scatter Radar facilities, the range extent of the detectable target is typically of the order of one thousand kilometers â about seven milliseconds â whereas the characteristic correlation time of the scattered signal varies from a few milliseconds in the D-region to only tens of microseconds in the F-region. If one is interested in estimating the scattering autocorrelation function (ACF) at time lags shorter than the F-region correlation time, the D-region must be considered as a moderately overspread target, whereas the F-region is a severely overspread one. Given the technical restrictions of the radar hardware, a combination of ATC and phase-coded long pulses is advantageous for this kind of target. We evaluate such an experiment under infinitely low signal-to-noise ratio (SNR) conditions using lag profile inversion. In addition, a qualitative evaluation under high-SNR conditions is performed by analysing simulated data. The results show that an acceptable estimation accuracy and a very good lag resolution in the D-region can be achieved with a pulse length long enough for simultaneous E- and F-region measurements with a reasonable lag extent. The new experiment design is tested with the EISCAT Tromsø VHF (224 MHz) radar. An example of a full D/E/F-region ACF from the test run is shown at the end of the paper
Using radar beam-parks to characterize the Kosmos-1408 fragmentation event
We describe the use of radar beam-park experiments to characterize the space debris resulting from a recent fragmentation event, the deliberate demolition of the defunct Kosmos-1408 satellite. We identify the Kosmos-1408 fragments and present distribution of measurement parameters as well as proxy orbit parameters. We present and apply a novel technique to estimate the size of objects by matching the signal to noise ratio of the detection to the radiation pattern of the radar. With this method we estimate the size distribution of the debris cloud. We also demonstrate how a pair of beam-park observations can be used to perform a crude, yet seemingly reliable, initial orbit determination. Finally, we present followup observations 5 months after the fragmentation that show a still compact cloud of debris
- âŚ