New techniques in ground-based ionospheric sounding and studies (original) (raw)
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Radiophysics and Quantum Electronics, 2011
We present the results of multi-instrument experiments related to studying the phenomena in the high-latitude ionosphere affected by high-power radio waves using the EISCAT technical facilities. It was found for the first time that strong small-scale artificial field-aligned irregularities (AFAIs) are excited when the ionospheric F region is heated by a high-power HF radio wave with X-mode polarization near the altitude at which the critical frequency f xF 2 of the F 2 layer is equal to the frequency f H of the heating accompanied by an up to 50% increase in the electron temperature. The spatial structure of the artificially perturbed ionospheric F region is examined in detail using an incoherent scatter radar operated in the regime of scanning over elevation angles from 92 • to 74 • with a 2 • step. It is shown that the spatial size of the heated patch strongly depends on the angle of the HF pumping relative to the Earth's magnetic field. The phenomena occurring in the artificially modified ionospheric F region heated at frequencies near the third electron gyroharmonic, i.e., at f H = 3f ce = f UH , where f UH is the upper-hybrid frequency, are explored on the basis of multi-instrument observation data.
Journal of Atmospheric and Solar-Terrestrial Physics, 2008
During the International Polar Year (IPY), one area of great interest is co-coordinated, multi-instrument probing of the ionosphere at high latitudes. This region is important not only for the applications that rely upon our understanding of it, but also because it contains the footprints of processes that have their origin in the interplanetary space. Many different techniques are now available for probing the ionosphere, from radar measurements to the analysis of very low frequency (VLF) wave paths. Combining these methods provides the ability to study the ionosphere from high in the F-region to the bottom of the D-layer. Thus, coupling processes from the magnetosphere and to the neutral atmosphere can be considered. An additional dimension is through comparisons of the response of the two polar ionospheres to similar (or the same) geomagnetic activity. With more instruments available at the South Pole inter-hemispheric, studies have become easier to accomplish such that a fuller picture of the global response to Sun-Earth coupling can be painted. This paper presents a review of the current state of knowledge in ionospheric probing. It cannot provide a comprehensive guide of the work to date due to the scale of the topic. Rather it is intended to give an overview of the techniques and recent results from some of the instruments and facilities that are a part of the IPY cluster 63-Heliosphere Impact on Geospace. In this way it is hoped that the reader will gain a flavor of the recent research performed in this area and the potential for continuing collaboration and capabilities during the IPY
Study of D, E And F Regions Of Ionosphere
The D-region of the ionosphere is remotely probed by ground-based radar. The method used is referred to as the partial reflection-drift experiment. The partial-reflection experiment is used to determine the horizontal-drift velocity of ionized irregularities in the ionosphere. If a point radio source is used, the stratified irregularities produce a diffraction pattern over the ground. By sensing this diffraction pattern with a minimum of three antennas the horizontal-drift velocity can be computed. To determine the horizontal-drift velocity of the ionosphere it is necessary to illuminate the ionosphere with a single radio-wave point source. When this is done a diffraction pattern is formed from the ionosphere irregularities in the D-region. The E and F region of ionosphere is studied using the ionospheric data from archives of ionospheric station. The ionospheric datas were used for training neural networks (NNs) to predict the parameters required to produce the final profile. The NNs have been trained to predict the individual ionospheric characteristics and coefficients that were required to describe the profile.
IEEE Geoscience and Remote Sensing Letters, 2018
In this letter, we present a prototype of an RF signal receiver operating in the HF band, whose design considers the use of software-defined radio signal processing technology, based on field-programmable gate arrays (FPGA) reconfigurable hardware and the use of gnuradio open software. The purpose of this letter is to improve the measurement rate at a fixed frequency of the reflection height, which is now obtained with a rate of 15 min using the IPS-42 ionosonde. The proposed method uses a pulse generated by the Canadian Advanced Digital Ionosonde as the transmitted signal. For the receiving section, the FPGA-based "Universal Software Radio Peripheral 1" was directly connected to a PC, where the return signals were analyzed by gnuradio. The measurements are taken with 1-min cadence, approximately, and are validated by comparing them with 15-min measurements taken with a colocated IPS-42 ionosonde. The acquisition rate of order 1 every minute is of interest in the study of a number of physical processes, i.e., traveling ionospheric disturbance, disturbances generated by seismic events, meteorological processes, and so on.
Journal of Geophysical Research, 1997
During the late austral summer of 1995-1996 we operated an HF digital ionosonde located at Casey, Antarctica (66.3øS, 110.5øE, -80.8 ø corrected geomagnetic (CGM) latitude), in an experimental drift mode with the aim of resolving the height variation of drift velocity in the polar cap ionosphere. We devised control programs for a Digisonde Portable Sounder 4 to collect data at separate frequency-range gates corresponding to the E and F regions to investigate the differences in their motions. During a 4-day campaign commencing March 11, 1996, the mode values of the drift perpendicular to the magnetic field (V.) were 85 rn s -• in the E region and 485 m s -• in the F region (using 10 m s -• bins and echoes from all heights in each region). Vertical profiles of drift velocity were obtained by sorting echoes into 10-km group-height bins. For measurements obtained within +3 hours of magnetic noon the average profile showed that in the lower E region V; increased approximately exponentially with true height. The corresponding velocity scale height was <9.0 km at 105 km, where the gradient was >46.7 1 1 1 rn s-km-. The mean value of V; leveled off to about 700 rn s-above 120 km, where it remained up to the F region peak height. The vertical gradient was caused by the increase in collision frequencies at the lower heights. The F region field-aligned component of drift (Vll) showed a strong diurnal variation, with mean values of -30 m s -• near noon and +60 m s -• during the night at a height of 180 km. The average over the whole day reveals a net upward drift of 30 m s -•. This behavior is attributed to the interaction between the meridional components of the generally antisunward neutral wind (Us) and perpendicular drift (V;s) moving plasma down the field lines during the day and up the field lines during the night, with Us and V;s having net equatorward values when averaged over all day. While the E region drift direction tended to be aligned with the basic antisunward convection which dominates the F region above Casey, it also tended to show greater temporal variability in direction, suggesting a smaller-scale size and lifetime for the E region structures giving rise to the echoes. There were events lasting over 2 hours during which the drifts in the two regions were clearly resolved into different azimuths (by nearly 180 ø for two events). These transient directional shears show the time variability in the phase transition between an F region collisionless, magnetized plasma driven by the E x BIB 2 convection to an E region collisional, unmagnetized plasma driven by E and irregular neutral winds. Paper number 97JA01944. 0148-0227/97/97JA-01944509.00
Advances in Space Research, 2004
Electromagnetic waves originating on Earth and recorded in space allow retrieval of ionospheric parameters. Using the Fast Onboard Recording of Transient Events satellite (FORTÉ ), it has been shown that trans-ionospheric pulsed radio-frequency (RF) signals carry sufficient information to infer the peak electron density of the ionosphere, in addition to the total electron content along a ray path between a source and a receiver. In this paper the detailed refractive properties of the ionosphere and the birefringent splitting of RF waves in the EarthÕs magnetic field are modeled using the Appleton-Hartree equation and an electron density profile based on the International Reference Ionosphere (IRI). Applications of this model to FORTÉ data provide additional information on the vertical profile of ionospheric plasma density at the time and place of measurement. Results of the FORTÉ observations are compared with the IRI. Published by Elsevier Ltd on behalf of COSPAR.
The resolving power of radio sounding methods for ionospheric parameter reconstruction
Advances in Space Research, 2001
The r.m.s, errors in ionospheric parameters studied by the vertical HF-sounding method were determined for a monotonic height distribution of the electron density. Numerical estimates were obtained for errors in real heights, in vertical velocities of plasma motion and in effective electron collision frequencies deduced from experimental measurements of virtual heights, Doppler frequency shift and radio wave absorption respectively. Their dependencies on signal polarisation, working frequency range and geo-magnetic latitude of the observation point were determined.
Geomagnetism and Aeronomy, 2009
The experimental studies of the specific behavior of small scale artificial ionospheric irregularities at midlatitudes, performed using the Sura HF heating facility, are analyzed. The observations were performed in September 2006, using the method of bi static backscatter by artificial ionospheric irregularities on the Armavir-Sura-St. Petersburg and Samara-Sura-Rostov on Don diagnostic paths. It has been detected that the Doppler frequency shift of scattered signals at 3-7 Hz was split on the Armavir-Sura-St. Petersburg path from 1500 to 1600 UT on September 6, 2006. The simultaneous measurements on the Samara-Sura-Rostov on Don path indicated that only one signal of bi static backscatter was present. An analysis of the experimental data, performed using the numerical simulation results, indicated that the ordinary and extraor dinary polarization modes of bi static backscatter signals could be simultaneously observed on September 6, 2006, on the Armavir-Sura-St. Petersburg path. PACS numbers: 94.20.dg, 94.20.Tt