On Pfister's theorem and its generalization

Bennett, J. A.; Dyson, P. L.

doi:10.1016/0021-9169(93)90055-4

Cited by 5 publications

(4 citation statements)

References 7 publications

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“…11, we estimated that X≤0.75 and 0.5≤n≤1.0 for 2 MHz oblique echoes with zenith angles ≤30 • . The irregularity velocities V i derived directly from the general form of Pfisters' theorem (Bennett and Dyson, 1993), k·V i =π f (where k ∼ =nk0 is the radar wave vector at the scatter center and f is the measured Doppler frequency shift), were clearly underestimated by V DDA ( ∼ =nV i ). If one assumes that the aspect angle is nearly zero at the scatter center, then the measured Doppler shift is directly proportional to the irregularity velocity amplitude V i (with k and V i being almost aligned).…”

Section: Estimation Of Apparent Velocities Of Doppler Spectra Side-pementioning

confidence: 99%

“…The Bragg scatter or irregularity apparent velocity amplitude V DDA obtained above does not include refraction effects. The estimated vertical and horizontal velocities were obtained from the direct application of Pfister's theorem which simply relates the echo angle-of-arrival (AOA), Doppler shift and velocity of the reflection point, viz., Pfister, 1971;Bennett and Dyson, 1993). The UMLCAR Digisonde Drift Analysis package used for the computations assumed that the refractive index n=1 at the scatter center or equivalently that the radar wave vector remained equal to its free space value k 0 along the radio-wave path.…”

Section: Estimation Of Apparent Velocities Of Doppler Spectra Side-pementioning

confidence: 99%

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Southern high-latitude Digisonde observations of ionosphere E-region Bragg scatter during intense lacuna conditions

et al. 2004

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Abstract. During summer months at solar cycle minimum, F-region lacuna and slant-Es conditions (SEC) are common features of daytime ionograms recorded around local magnetic noon at Casey, Antarctica. Digisonde measurements of drift velocity height profiles show that the occurrence of lacuna prevents the determination of F-region drift velocities and also affects E-region drift velocity measurements. Unique E-region spectral features revealed as intervals of Bragg scatter superimposed on typical background Eregion reflection were observed in Digisonde Doppler spectra during intense lacuna conditions. Daytime E-region Doppler spectra recorded at carrier frequencies from 1.5 to 2.7 MHz, below the E-region critical frequency f o E, have two side-peaks corresponding to Bragg scatter at approximately ±1-2 Hz symmetrically located on each side of a centralpeak corresponding to near-zenith total reflections. Angleof-arrival information and ray-tracing simulations show that echo returns are coming from oblique directions most likely resulting from direct backscatter from just below the total reflection height for each sounding frequency. The Bragg backscatter events are shown to manifest during polar lacuna conditions, and to affect the determination of E-region background drift velocities, and as such must be considered when using standard Doppler-sorted interferometry (DSI) techniques to estimate ionospheric drift velocities. Given the Doppler and spatial separation of the echoes determined from high-resolution Doppler measurements, we are able to estimate the Bragg scatter phase velocity independently from the bulk E-region motion. The phase velocity coincides with the E×B direction derived from in situ fluxgate magnetometer records. When ionospheric refraction is considered, the phase velocity amplitudes deduced from DSI are comparable to the ion-acoustic speed expected in the E-region. We briefly consider the plausibility that these previously unreported polar cap E-region Bragg scatter Doppler spectral signatures, observed at Casey in December 1996 during SEC/lacunaCorrespondence to: R. J. Morris (ray.morris@aad.gov.au) conditions may be linked to ionosphere irregularities. These irregularities may possibly be generated by primary plasma waves triggered by current-driven instabilities, that is to say, a hybrid of the "modified two-stream" and "gradient drift" instability mechanisms.

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Section: Estimation Of Apparent Velocities Of Doppler Spectra Side-pementioning

confidence: 99%

Section: Estimation Of Apparent Velocities Of Doppler Spectra Side-pementioning

confidence: 99%

Southern high-latitude Digisonde observations of ionosphere E-region Bragg scatter during intense lacuna conditions

et al. 2004

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“…In doing so, he found that the interferometric wind velocities were in good agreement with the velocities obtained with the method of similar fades. While the Pfister (1971) results are for total ionospheric reflections, Bennett and Dyson (1993) later showed that this result generally applied when fixed ground sites were used to observe an ionosphere that moved without change of shape. This means that the same conclusions that apply to simple IDI in the MLT, namely that similar-fade apparent velocities correspond to the case for which changes in the backscatter, or equivalently, in the ground diffraction pattern over time, are not adequately accounted for, apply to the case of total reflections from the ionosphere.…”

Section: Imaging Doppler Interferometrymentioning

confidence: 99%

MF and HF radar techniques for investigating the dynamics and structure of the 50 to 110 km height region: a review

Reid

2015

Prog. in Earth and Planet. Sci.

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The application of medium-frequency (MF) and high-frequency (HF) partial reflection radar to investigate the neutral upper atmosphere is one of the oldest such techniques still regularly in use. The techniques have been continuously improved and remain a robust and reliable method of obtaining wind velocities, turbulence intensities, electron densities, and measurements of atmospheric structure in the mesosphere lower thermosphere (MLT) region (50 to 110 km). In this paper, we review recent developments, discuss the strengths and weaknesses of the technique, and consider possible improvements.

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“…It is important to appreciate that the Doppler shifts of echoes actually represent the integral of phase path changes over the radio wave propagation [Dyson, 1975;Bennett and Dyson, 1993]. These phase path changes may be caused by the bulk motion of the plasma or by photochemistry.…”

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confidence: 99%

Analysis of direction‐of‐arrival aliasing for MF/HF Doppler‐sorted interferometry measurements of ionospheric drift

Parkinson¹,

Dyson²,

Smith³

1997

Radio Science

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Abstract. The determination of accurate direction of arrival (DOA) of echoes is paramount when performing Doppler-sorted interferometry (DSI) at MF/HF to measure the drift of ionospheric plasma. Important factors affecting the accuracy include inadequate signal-to-noise ratio (SNR) and coherency of ionospheric echoes. As the SNR deteriorates, there is an increase in the errors in the phases measured at the individual antennas of an array, and this leads to ambiguities in DOA equivalent to directional aliasing. In this paper we model this effect, the effects of Doppler-frequency aliasing, and the finite resolution of Doppler spectra. We thereby show the importance for vertical incident sounders of rejecting echoes with large off-vertical angles, and the choice of appropriate signal-processing parameters for the accurate estimation of ionospheric motions. As an example, we consider the situation for vertical incident ionosondes and show that a low SNR can produce spurious echoes at relatively large zenith angles, which can, however, be avoided or minimized by the suitable choice of operating parameters.

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On Pfister's theorem and its generalization

Cited by 5 publications

References 7 publications

Southern high-latitude Digisonde observations of ionosphere E-region Bragg scatter during intense lacuna conditions

Southern high-latitude Digisonde observations of ionosphere E-region Bragg scatter during intense lacuna conditions

MF and HF radar techniques for investigating the dynamics and structure of the 50 to 110 km height region: a review

Analysis of direction‐of‐arrival aliasing for MF/HF Doppler‐sorted interferometry measurements of ionospheric drift

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