Direct measurements on imaging riometer antenna array beam directivities

Wilson, A.; Nel, J. J.; Mathews, Marc J.; Stoker, P. H.

doi:10.1029/2000rs002509

Cited by 5 publications

(10 citation statements)

References 4 publications

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“…[17] The viewing directions of the 64-element imaging riometer were measured directly by flying a radio transmitter, mounted underneath a helicopter, across the riometer antenna array. Variations in signal strength, recorded when the helicopter path crossed a beam, were found to compare well with the theoretically calculated directivities within accuracy limits set by position determinations by the GPS [Wilson et al, 2001].…”

Section: Accuracy Of the Viewing Directionssupporting

confidence: 70%

“…Signals from 64 beam directions of the antenna matrix are obtained from an 8 × 8 Butler matrix, which serves as the phasing steering system. Each of eight riometers records during a sampling period of 1 s the signal strengths of a row of eight beam directions in a north‐to‐south sequence [ Wilson et al , 2001]. The antenna array is aligned geographically north‐south.…”

Section: Experimental Methodsmentioning

confidence: 99%

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Imaging riometer observations on energetic electron precipitation at SANAE IV, Antarctica

Wilson¹

2002

J. Geophys. Res.

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[1] The expansion phase of a substorm on the evening of 1 May 1997 was studied from recordings of all-sky optical aurora and a 64-beam imaging riometer at the Antarctic base SANAE IV (L = 4.1). Digitized all-sky, low-level white light images of auroral optical emissions were mapped onto the angular directivity functions of the 64-beam imaging riometer. During the period of investigation, several optical arcs appeared and disappeared, while a persistent absorption structure appeared in the south (poleward). This and new structures changed only slowly in time. The differences in morphologies of optical emissions and absorption regions, together with temporal differences, imply that there are two categories of energetic auroral electrons: the softer electrons (<10 keV) causing optical emissions in the E and F regions of the ionosphere and the harder (>10 keV) electrons ionizing down into the D region for cosmic radio noise absorption (CRNA). Optical emissions tend to lead the appearance of cosmic radio noise absorptions by 0-60 s in a specific region of ionospheric space. Furthermore, in the all-sky optical data, westward traveling surges (WTS) were observed coincident with a CRNA WTS and leading the CRNA WTS by $30-50 s. In the CRNA data the WTS was ribbon-like, traveling westward at a speed of 2.3 km s À1 . These observations suggest that the softer electrons, causing E and F region optical emissions, may be injected onto drift paths closer to Earth than the more energetic electrons, ionizing down into the D region for cosmic radio noise absorption. The harder electrons could have been accelerated by, for instance, an increasing dawn-to-dusk electric field for later precipitation.

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Section: Accuracy Of the Viewing Directionssupporting

confidence: 70%

Section: Experimental Methodsmentioning

confidence: 99%

Imaging riometer observations on energetic electron precipitation at SANAE IV, Antarctica

Wilson¹

2002

J. Geophys. Res.

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“…Riometers are primarily used to measure enhancement of the D-region ionosphere by energetic charged particle precipitation driven by magnetospheric electrodynamics (Stauning, 1984). The imaging riometer for ionospheric studies (IRIS) at SANAE has 8 × 8 antenna arrays and consists of 64 halfwavelength crossed-dipole (turnstile) antennas mounted one quarter of a wavelength above an artificial ground plane (Wilson et al, 2001). Similar to the imaging riometer at Halley, the riometer at SANAE operates on 38.2 MHz and samples a region of over 200 km × 200 km at 90 km altitude with 49 means every second (Detrick and Rosenberg, 1990).…”

Section: The Imaging Riometer At Sanaementioning

confidence: 99%

“…There have been no studies of short-period GWs using the South Africa National Antarctic Expedition (SANAE, 72 • S, 3 • W) imaging riometer before. Some of the studies which employed this instrument include the observation of energetic electron precipitation at SANAE IV, Antarctica, by Wilson and Stoker (2002), and spatial structures in enhanced ionization of the ionosphere observed by absorption of cosmic radio waves by Wilson et al (2001).…”

Section: Introductionmentioning

confidence: 99%

Extracting gravity wave parameters during the September 2002 Southern Hemisphere major sudden stratospheric warming using a SANAE imaging riometer

Mbatha

Sivakumar

Benchérif³

et al. 2013

Ann. Geophys.

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Abstract. Using absorption data measured by imaging riometer for ionospheric studies (IRIS) located at the South Africa National Antarctic Expedition (SANAE), Antarctica (72 • S, 3 • W), we extracted the parameters of gravity waves (GW) of periods between 40 and 50 min during late winter/spring of the year 2002, a period of the unprecedented major sudden stratospheric warming (SSW) in the Southern Hemisphere middle atmosphere. During this period, an unprecedented substantial increase of temperature by about 25-30 K throughout the stratosphere was observed. During the period of the occurrence of the major stratospheric warming, there was a reduction of both the GW horizontal phase speeds and the horizontal wavelengths at 90 km. The GW phase speeds and horizontal wavelengths were observed to reach minimum values of about 7 m s −1 and 19 km, respectively, while during the quiet period the average value of the phase speed and horizontal wavelength was approximately 23 m s −1 and 62 km, respectively. The observed event is discussed in terms of momentum flux and also a potential interaction of gravity waves, planetary waves and mean circulation.

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“…From these observations it is possible to derive a spatial map of the attenuation in the ionosphere as a function of time. Typical resolutions used are 7 by 7 [ Detrick and Rosenberg, 1990] and 8 by 8 [ Wilson et al, 2001], giving 49 and 64 areas of observation respectively.…”

Section: Introductionmentioning

confidence: 99%

Determining riometer quiet day curves 1. The matrix method

Drevin

Stoker

2003

Radio Science

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[1] A number of methods have been proposed for the determination of quiet day curves of riometer recordings of cosmic radio noise in polar regions. Most of these methods are based on the distribution of the recorded intensities, in a given siderial time period, over a number of consecutive days. The method proposed in this paper is based on the filtering, using a low-pass filter in the Fourier domain, of a discrete two-dimensional function or matrix. The two dimensions of the matrix are siderial time and day number, with each row of the matrix representing one siderial day. With a low-pass filter the low frequency Fourier coefficients are retained while the high frequency Fourier coefficients are discarded. The highest Fourier coefficient that is retained is the cutoff frequency of the filter. The proposed method was compared to two existing methods using data obtained from a single broad beam antenna. It was found that the proposed method is less sensitive to noise than the existing methods.INDEX TERMS: 6964 Radio Science: Radio wave propagation; 6982 Radio Science: Tomography and imaging; 6974 Radio Science: Signal processing; Citation: Drevin, G. R., and P. H. Stoker, Determining riometer quiet day curves 1. The matrix method,

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Direct measurements on imaging riometer antenna array beam directivities

Cited by 5 publications

References 4 publications

Imaging riometer observations on energetic electron precipitation at SANAE IV, Antarctica

Imaging riometer observations on energetic electron precipitation at SANAE IV, Antarctica

Extracting gravity wave parameters during the September 2002 Southern Hemisphere major sudden stratospheric warming using a SANAE imaging riometer

Determining riometer quiet day curves 1. The matrix method

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