115 research outputs found
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
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 high‐power, large‐aperture radar transmitter with several large‐aperture receiving arrays to make a geospace radar—a radar capable of probing near‐Earth space from the upper troposphere through to the solar corona—would 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 radio‐array 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
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
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. ©2020. 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 – about seven milliseconds – 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
GNSS Observations of Ionospheric Variations During the 21 August 2017 Solar Eclipse
An edited version of this paper was published by AGU. Copyright 2017 American Geophysical Union.
Coster, A.J., Goncharenko, L., Zhang S.-R., Erickson, P.J., Rideout, W. & Vierinen, J. (2017). GNSS Observations of Ionospheric Variations During the 21 2 August 2017 Solar Eclipse. Geophysical Research Letters, 44(24), 12041-12048. https://doi.org/10.1002/2017GL075774. To view the published open abstract, go to https://doi.org/10.1002/2017GL075774.On 21 August 2017, during daytime hours, a total solar eclipse with a narrow ∼160 km wide umbral shadow occurred across the continental United States. Totality was observed from the Oregon coast at ∼9:15 local standard time (LST) (17:20 UT) to the South Carolina coast at ∼13:27 LST (18:47 UT). A dense network of Global Navigation Satellite Systems (GNSS) receivers was utilized to produce total electron content (TEC) and differential TEC. These data were analyzed for the latitudinal and longitudinal response of the TEC and for the presence of traveling ionospheric disturbances (TIDs) during eclipse passage. A significant TEC depletion, in some cases greater than 60%, was observed associated with the eclipse shadow, exceeding initial model predictions of 35%. Evidence of enhanced large‐scale TID activity was detected over the United States prior to and following the large TEC depletion observed near the time of totality. Signatures of enhanced TEC structures were observed over the Rocky Mountain chain during the main period of TEC depletion
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