scholarly journals <i>Letter to the Editor:</i> First complementary observations by ionospheric tomography, the EISCAT Svalbard radar and the CUTLASS HF radar

1998 ◽  
Vol 16 (11) ◽  
pp. 1519-1522 ◽  
Author(s):  
C. N. Mitchell ◽  
I. K. Walker ◽  
S. E. Pryse ◽  
I. Kersley ◽  
I. W. McCrea ◽  
...  
Keyword(s):  
Auroral Zone ◽  
Hf Radar ◽  
Auroral Ionosphere ◽  
Polar Cap ◽  
Low Velocity ◽  
Radio Science ◽  
Ionospheric Tomography ◽  
Ionospheric Physics ◽  
Incoherent Scatter ◽  
Complementary Nature

Abstract. Experimental results are presented from ionospheric tomography, the EISCAT Svalbard radar and the CUTLASS HF radar. Tomographic measurements on 10 October 1996, showing a narrow, field-aligned enhancement in electron density in the post-noon sector of the dayside auroral zone, are related to a temporal increase in the plasma concentration observed by the incoherent scatter radar in the region where the HF radar indicated a low velocity sunwards convection. The results demonstrate the complementary nature of these three instruments for polar-cap ionospheric studies.Key words. Ionosphere · Auroral ionosphere · Polar ionosphere · Radio science (ionospheric physics)

scholarly journals Ground clutter cancellation in incoherent radars: solutions for EISCAT Svalbard radar

2000 ◽  
Vol 18 (9) ◽  
pp. 1242-1247 ◽  
Author(s):  
T. Turunen ◽  
J. Markkanen ◽  
A. P. van Eyken
Keyword(s):  
Subtraction Method ◽  
Free Electrons ◽  
Simple Manner ◽  
Radio Science ◽  
Ionospheric Physics ◽  
Incoherent Scatter ◽  
Ground Clutter ◽  
Incoherent Scatter Radars ◽  
Instruments And Techniques ◽  
Physics Signal

Abstract. Incoherent scatter radars measure ionosphere parameters using modified Thomson scatter from free electrons in the target (see e.g. Hagfors, 1997). The integrated cross section of the ionospheric scatterers is extremely small and the measurements can easily be disturbed by signals returned by unwanted targets. Ground clutter signals, entering via the antenna side lobes, can render measurements at the nearest target ranges totally impossible. The EISCAT Svalbard Radar (ESR), which started measurements in 1996, suffers from severe ground clutter and the ionosphere cannot be measured in any simple manner at ranges less than about 120–150 km, depending on the modulation employed. If the target and clutter signals have different, and clearly identifiable, properties then, in principle, there are always ways to eliminate the clutter. In incoherent scatter measurements, differences in the coherence times of the wanted and unwanted signals can be used for clutter cancellation. The clutter cancellation must be applied to all modulations, usually alternating codes in modern experiments, used for shorter ranges. Excellent results have been obtained at the ESR using a simple pulse-to-pulse clutter subtraction method, but there are also other possibilities.Key words: Radio science (ionospheric physics; signal processing; instruments and techniques)

scholarly journals High-latitude propagation studies using a meridional chain of LF/MF/HF receivers

2004 ◽  
Vol 22 (5) ◽  
pp. 1705-1718 ◽  
Author(s):  
J. LaBelle
Keyword(s):  
High Latitude ◽  
Auroral Zone ◽  
Magnetic Storms ◽  
Dartmouth College ◽  
Propagation Characteristics ◽  
Radio Science ◽  
Ionospheric Physics ◽  
Ionospheric Propagation ◽  
Latitude Range ◽  
Storms And Substorms

Abstract. For over a decade, Dartmouth College has operated programmable radio receivers at multiple high-latitude sites covering the frequency range 100-5000kHz with about a 1-s resolution. Besides detecting radio emissions of auroral origin, these receivers record characteristics of the ionospheric propagation of natural and man-made signals, documenting well-known effects, such as the diurnal variation in the propagation characteristics of short and long waves, and also revealing more subtle effects. For example, at auroral zone sites in equinoctial conditions, the amplitudes of distant transmissions on MF/HF frequencies are often enhanced by a few dB just before they fade away at dawn. The polarization and/or direction of the arrival of ionospherically propagating signals in the lower HF range (3-5MHz) show a consistent variation between pre-midnight, post-midnight, and pre-dawn conditions. As is well known, magnetic storms and substorms dramatically affect ionospheric propagation; data from multiple stations spanning the invariant latitude range 67-79° reveal spatial patterns of propagation characteristics associated with magnetic storms and substorms. For example, in the hours preceding many isolated substorms, favorable propagation conditions occur at progressively lower latitudes as a function of time preceding the substorm onset. For some of these effects, explanations follow readily from elementary ionospheric physics, but understanding others requires further investigation.Key words. Magnetospheric physics (annual phenomena) – Radio science (ionosphere propagation; radio-wave propagation)6

scholarly journals Space Plasma Exploration by Active Radar (SPEAR): an overview of a future radar facility

2000 ◽  
Vol 18 (9) ◽  
pp. 1248-1255 ◽  
Author(s):  
D. M. Wright ◽  
J. A. Davies ◽  
T. R. Robinson ◽  
P. J. Chapman ◽  
T. K. Yeoman ◽  
...  
Keyword(s):  
Plasma Physics ◽  
Space Plasma ◽  
Hf Radar ◽  
Polar Cap ◽  
Radio Science ◽  
Plasma Irregularities ◽  
Extensive Field ◽  
Instruments And Techniques ◽  
Technical Specifications ◽  
Artificial Plasma

Abstract. SPEAR is a new polar cap HF radar facility which is to be deployed on Svalbard. The principal capabilities of SPEAR will include the generation of artificial plasma irregularities, operation as an 'all-sky' HF radar, the excitation of ULF waves, and remote sounding of the magnetosphere. Operation of SPEAR in conjunction with the multitude of other instruments on Svalbard, including the EISCAT Svalbard radar, and the overlap of its extensive field-of-view with that of several of the HF radars in the SuperDARN network, will enable in-depth diagnosis of many geophysical and plasma phenomena associated with the cusp region and the substorm expansion phase. Moreover, its ability to produce artificial radar aurora will provide a means for the other instruments to undertake polar cap plasma physics experiments in a controlled manner. Another potential use of the facility is in 'field-line tagging' experiments, for coordinated ground-satellite experiments. Here the scientific objectives of SPEAR are detailed, along with the proposed technical specifications of the system.Key words: Ionosphere (active experiments) – Radio science (instruments and techniques) – Space plasma physics (instruments and techniques)

scholarly journals The effects of high-frequency ULF wave activity on the spectral characteristics of coherent HF radar returns: a case study

2004 ◽  
Vol 22 (5) ◽  
pp. 1843-1849
Author(s):  
D. M. Wright ◽  
T. K. Yeoman ◽  
E. E. Woodfield
Keyword(s):  
High Frequency ◽  
Spectral Power ◽  
Spectral Characteristics ◽  
Wave Activity ◽  
Hf Radar ◽  
Mhd Waves ◽  
Closed Field ◽  
Radio Science ◽  
Ionospheric Physics ◽  
Field Lines

Abstract. It is now a common practice to employ ground-based radars in an attempt to distinguish between those regions of the Earth's upper atmosphere which are magnetically conjugate to open and closed magnetic field lines. Radar returns from ionospheric irregularities inside the polar cap and cusp regions generally exhibit large spectral widths in contrast to those which exist on closed field lines at lower latitudes. It has been suggested that the so-called Spectral Width Boundary (SWB) might act as a proxy for the open-closed field line boundary (OCFLB), which would then be an invaluable tool for investigating reconnection rates in the magnetosphere. The exact cause of the increased spectral widths observed at very high latitudes is still subject to considerable debate. Several mechanisms have been proposed. This paper compares a dusk-sector interval of coherent HF radar data with measurements made by an induction coil magnetometer located at Tromsø, Norway (66° N geomagnetic). On this occasion, a number of equatorward excursions of the SWB in the radar backscatter are accompanied by increases in spectral power of ULF waves in the Pc1-2 frequency band as the SWB passes overhead. Thus, these observations support the possibility that high-frequency magnetospheric wave activity at least contribute to the observed spectral characteristics and that such wave activity might play a significant role in the nightside ionosphere. Key words. Ionosphere (auroral ionosphere) – Magnetospheric physics (MHD waves and instabilities) – Radio science (ionospheric physics)

scholarly journals Decoding of Barker-coded incoherent scatter measurements by means ofmathematical inversion

2004 ◽  
Vol 22 (1) ◽  
pp. 3-13 ◽  
Author(s):  
B. Damtie ◽  
M. S. Lehtinen ◽  
T. Nygrén
Keyword(s):  
Matched Filter ◽  
Mirror Image ◽  
Inversion Method ◽  
Statistical Accuracy ◽  
Radio Science ◽  
Ionospheric Physics ◽  
Range Ambiguity ◽  
Incoherent Scatter ◽  
Instruments And Techniques ◽  
Better Than

Abstract. The standard analysis of Barker-coded incoherent scatter experiments is based on a matched filter with an impulse response which is a mirror image of the code itself. The method produces small sidelobes which cause contamination from regions outside the nominal range gate. A corresponding effect is also encountered in the lag direction, where individual lag estimates are biased by the variation of the plasma autocorrelation function around the nominal lag value. The present paper introduces a new method of analysing Barker-coded experiments by means of stochastic inversion. Since it does not apply a decoding filter, it does not suffer from drawbacks caused by the sidelobes of the range ambiguity function. The method combines the profile of each full lag and a number of surrounding fractional lags into a single inversion problem. Error analysis also indicates that the statistical accuracy given by inversion is better than that obtained by means of standard decoding. Furthermore, the inversion method gives a possibility to reduce the bias due to the variation of the autocorrelation around the nominal lag. In this paper the method is described and applied to data obtained by means of the EISCAT Svalbard radar. In addition, it is shown that mathematical inversion can be used instead of the the conventional height integration. Key words. Radio science (ionospheric physics; signal processing; instruments and techniques)

scholarly journals The spatial structure of the dayside ionospheric trough

1998 ◽  
Vol 16 (10) ◽  
pp. 1169-1179 ◽  
Author(s):  
S. E. Pryse ◽  
L. Kersley ◽  
M. J. Williams ◽  
I. K. Walker
Keyword(s):  
Large Scale ◽  
Satellite System ◽  
Plasma Electron ◽  
Polar Ionosphere ◽  
Polar Cap ◽  
Ionospheric Electron Density ◽  
Radio Science ◽  
Additional Information ◽  
Incoherent Scatter ◽  
Eiscat Radar

Abstract. Tomographic imaging provides a powerful technique for obtaining images of the spatial distribution of ionospheric electron density at polar latitudes. The method, which involves monitoring radio transmissions from the Navy Navigation Satellite System at a meridional chain of ground receivers, has particular potential for complementing temporal measurements by other observing techniques such as the EISCAT incoherent-scatter radar facility. Tomographic reconstructions are presented here from a two-week campaign in November 1995 that show large-scale structuring of the polar ionosphere. Measurements by the EISCAT radar confirm the authenticity of the technique and provide additional information of the plasma electron and ion temperatures. The dayside trough, persistently observed at high latitudes during a geomagnetically quiet period but migrating to lower latitudes with increasing activity, is discussed in relationship to the pattern of the polar-cap convection.Key words. Ionosphere-magnetosphere interactions · Polar ionosphere · Radio science · Ionospheric propagation

scholarly journals Probing discrete auroral arcs by ionospheric tomography

1998 ◽  
Vol 16 (5) ◽  
pp. 574-582 ◽  
Author(s):  
J. Moen ◽  
S. T. Berry ◽  
L. Kersley ◽  
B. Lybekk
Keyword(s):  
Electron Density ◽  
Optical Observations ◽  
Precipitation Event ◽  
Radio Science ◽  
Ionospheric Tomography ◽  
Ionospheric Physics ◽  
Radio Signals ◽  
A Chain ◽  
Auroral Phenomena ◽  
Auroral Arcs

Abstract. Optical observations of 557.7 nm and 630.0 nm emissions from discrete auroral arcs in the post-noon sector have been related to localised field-aligned enhancements in the spatial distribution of E- and F-layer electron density respectively seen in images reconstructed by ionospheric tomography. Results from two case studies are presented in which meridian scanning photometer and all-sky camera observations on Svalbard have been compared to electron-density structures found by tomographic inversion of measurements made by reception of radio signals at a chain of four stations at high latitude. The F-layer features are long-lived and show exact correspondence to the red-line emissions. Transient arcs in green-line intensity result in E-region structures that are resolved in one case, but not in another where the dynamic auroral forms are separated by less than one degree of latitude. The signature of an inverted-V precipitation event is clearly evident in one example.Key words. Ionosphere (Auroral ionosphere) · Magnetospheric physics (Auroral phenomena) · Radio science (Ionospheric physics)

scholarly journals Meteor fluxes and visual magnitudes from EISCAT radar event rates: a comparison with cross-section based magnitude estimates and optical data

1998 ◽  
Vol 16 (11) ◽  
pp. 1475-1485 ◽  
Author(s):  
A. Pellinen-Wannberg ◽  
A. Westman ◽  
G. Wannberg ◽  
K. Kaila
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Optical Measurement ◽  
Optical Observations ◽  
Optical Data ◽  
Radio Science ◽  
Ionospheric Physics ◽  
Incoherent Scatter ◽  
Visual Magnitude ◽  
Event Rates

Abstract. Incoherent scatter radars (ISR) are versatile instruments for continuous monitoring of ionisation processes in the Earth's atmosphere. EISCAT, The European Incoherent Scatter facility has proven effective also in meteor studies. The time resolution of the radar can be reduced to a few milliseconds, sufficient to resolve the passage of individual meteors through the narrow ISR beam. Methods for group and phase velocity determination of the meteoroids and the discrepancy between the results related to the target behaviour are presented. The radar cross sections of echoes associated with moving meteoroids ("meteor head echoes") are very small and increase with decreasing wavelength. The parent meteoroids are found to have visual magnitudes far below the detection limit of most optical observations. The equivalent visual magnitude limit of the smallest objects observed by EISCAT in the current experiments has been estimated by two different methods, both from the cross-section measurements and from the measured event rates. Both methods give a limit value of +10 for the smallest objects while the upper limit is +4. The lower limit of the visual magnitude for the collocated optical measurement system is +4. Thus the two detection systems observe two different meteor size ranges, with the radar almost reaching micrometeorite population. Meteor fluxes estimated from the event rates and the radar system parameters agree well with previous extrapolated values for this size range.Key words. Ionosphere (ionization mechanisms). Radio science (ionospheric physics). Space plasma physics (ionization processes)

Studies of the cusp and auroral zone with incoherent scatter radar: the scientific and technical case for a polar-cap radar

1990 ◽  
Vol 52 (6-8) ◽  
pp. 645-663 ◽  
Author(s):  
S.W.H. Cowley ◽  
A.P. van Eyken ◽  
E.C. Thomas ◽  
P.J.S. Williams ◽  
D.M. Wlllis
Keyword(s):  
Auroral Zone ◽  
Polar Cap ◽  
Incoherent Scatter Radar ◽  
Incoherent Scatter ◽  
Scatter Radar

scholarly journals On the occurrence and motion of decametre-scale irregularities in the sub-auroral, auroral, and polar cap ionosphere

2003 ◽  
Vol 21 (8) ◽  
pp. 1847-1868 ◽  
Author(s):  
M. L. Parkinson ◽  
J. C. Devlin ◽  
H. Ye ◽  
C. L. Waters ◽  
P. L. Dyson ◽  
...  
Keyword(s):  
Electric Fields ◽  
Spectral Width ◽  
Auroral Oval ◽  
Auroral Zone ◽  
Ionospheric Irregularities ◽  
Lower Latitude ◽  
Doppler Velocity ◽  
Auroral Ionosphere ◽  
Polar Cap ◽  
Sunspot Maximum

Abstract. The statistical occurrence of decametre-scale ionospheric irregularities, average line-of-sight (LOS) Doppler velocity, and Doppler spectral width in the sub-auroral, auroral, and polar cap ionosphere ( - 57°L to - 88°L) has been investigated using echoes recorded with the Tasman International Geospace Environment Radar (TIGER), a SuperDARN radar located on Bruny Island, Tasmania (147.2° E, 43.4° S geographic; - 54.6 °L). Results are shown for routine soundings made on the magnetic meridian beam 4 and the near zonal beam 15 during the sunspot maximum interval December 1999 to November 2000. Most echoes were observed in the nightside ionosphere, typically via 1.5-hop propagation near dusk and then via 0.5-hop propagation during pre-midnight to dawn. Peak occurrence rates on beam 4 were often > 60% near magnetic midnight and ~ - 70 °L. They increased and shifted equatorward and toward pre-midnight with increasing Kp (i.e. Bz southward). The occurrence rates remained very high for Kp > 4, de-spite enhanced D-region absorption due to particle precipitation. Average occurrence rates on beam 4 exhibited a relatively weak seasonal variation, consistent with known longitudinal variations in auroral zone magnetic activity (Basu, 1975). The average echo power was greatest between 23 and 07 MLT. Two populations of echoes were identified on both beams, those with low spectral width and a mode value of ~ 9 ms-1 (bin size of 2 ms-1) concentrated in the auroral and sub-auroral ionosphere (population A), and those with high spectral width and a mode value of ~ 70 ms-1 concentrated in the polar cap ionosphere (population B). The occurrence of population A echoes maximised post-midnight because of TIGER’s lower latitude, but the subset of the population A echoes observed near dusk had characteristics reminiscent of "dusk scatter" (Ruohoniemi et al., 1988). There was a dusk "bite out" of large spectral widths between ~ 15 and 21 MLT and poleward of - 67 °L, and a pre-dawn enhancement of large spectral widths between ~  03 and 07 MLT, centred on ~ - 61 °L. The average LOS Doppler velocities revealed that frequent westward jets of plasma flow occurred equatorward of, but overlapping, the diffuse auroral oval in the pre-midnight sector.Key words. Ionosphere (auroral ionosphere; electric fields and currents, ionospheric irregularities)

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