Use of refractive scattering to explain SHF scintillations

Crain, C. M.; Booker, Henry G.; Ferguson, J. A.

doi:10.1029/rs014i001p00125

Cited by 28 publications

(10 citation statements)

References 28 publications

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“…Intuitively, however, the sharp gradients associated with the rapid changes in the electron density will affectsthe radio waves quite differently than the turbulencelike irregularities. Crain et al [1979], in an effort to explain gigahertz scintillation, proposed a refractive scattering mechanism for the scintillation phenomenon in which they pointed out the importance of the sharp gradients. Thus, it seems that to understand the scintillation of radio waves through these bubbles, a different approach to the problem is required, one that does not depend on the assumption of statistical homogeneity of the medium and will take into account the effects due to the overall structures of the irregularities rather than depending solely on the power spectrum of the irregularities.…”

supporting

confidence: 88%

Model computations of radio wave scintillation caused by equatorial ionospheric bubbles

Wernik¹,

Liu²,

Yeh³

1980

Radio Science

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In situ data measured on board AE satellites and rockets reveal spiky and wedgelike electron density structures inside the equatorial ionospheric bubbles. Two models are constructed to simulate the initial stage and fully developed stage of a bubble. Effects of radio propagation through such bubbles are simulated by solving the parabolic equation numerically. The results show that even though the amplitude scintillation at 136 MHz appears to be stationary, such is not the case at gigahertz frequencies. Instead, the amplitude at gigahertz frequencies shows outbursts with large excursions whenever the direct ray intersects the spicky ionization structure. Both the peak‐to‐peak excursion and the amplitude distribution cannot be predicted by the scintillation theory that assumes the medium to be random.

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supporting

confidence: 88%

Model computations of radio wave scintillation caused by equatorial ionospheric bubbles

Wernik¹,

Liu²,

Yeh³

1980

Radio Science

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“…One important result of this study shows that even when the amplitude scintillations at VHF appears to be stationary, the GHz frequencies show outbursts with large excursions whenever the direct ray intersects a spiky ionization structure. In fact, this result validates the earlier arguments proposed by Crain et al (1979), while using refractive scattering mechanism, to explain SHF scintillations brought about by equatorial plasma bubbles. The plume structure is presumed to play a dominant role in providing the lens action needed to explain SHF scintillations.…”

Section: Introductionsupporting

confidence: 80%

Parametrization of spectra of plasma bubble induced VHF satellite scintillations and its geophysical significance

Vijayakumar

Pasricha

1997

Ann. Geophys.

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Abstract. An important component of ionospheric plasma irregularity studies in the Indian low latitudes involves the study of the plasma bubbles which produce intense scintillations of the transionospheric satellite signals. Many such plasma bubble induced (PBI) scintillation events were identified while recording 244 MHz signal from the geostationary satellite Fleetsat (73°E) at Delhi (28.6°N, 77.2°E) during March-April 1991. This type of scintillations represents changes in plasma processes. These scintillations are spectrally analyzed using an autoregressive (AR) scheme, which is equivalent to maximum entropy method of spectrum analysis, amenable to extracting optimum spectral content from short data lengths (20 -40 s). Each spectrum is assigned a level of detectability using the final prediction error (FPE) derived from the optimum filter order required to resolve the spectrum. Lower detectability together with a higher order filter indicate a higher level of coherence for the plasma irregularities (discrete structures). Consistent patterns for these scintillations emerge from the present analysis as follows: (1) the initial and final phases of a scintillation patch display quasiperiodic oscillations. Their corresponding spectra show dominant (Gaussian shaped) spectral features with detectability levels of )6 dB to )12 dB and requiring a higher order (>6) AR filter for their spectral resolution. These are most likely associated with discrete ''filament-like'' or ''sheet-like'' plasma structures that exist near the bubble walls. (2) Two main features of the scintillation spectra could be positively associated with the welldeveloped plasma bubble stage: (a) spectra displaying a power-law process with a single component spectral slope between 1.6 to 3.0. Generally such spectra are resolved with a 2nd order filter and have a 1 dB to 6 dB of detectability. (b) Spectra displaying a double slope, indicating an inner and an outer scale regime for the power-law irregularities. These spectra are resolved with higher order filters (>3 but <7) and possess detectability levels of )1 dB to 3 dB. These spectra display finer spectral changes, perhaps indicative of the nature of continuously evolving plasma irregularities. As an example, an analysis of a single scintillation patch is presented to highlight the geophysical significance of the present approach. Some important parameters used in the AR scheme of spectral analysis are given in the Appendix.

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“…value of S 4 is greater than unity when the phase SDF is more steeply sloped than , (g4• 2) increases without bound as qo approaches zero, but this is of no consequence in the theory. Indeed, the validity of the weak-scatter theory depends only on the magnitude of U', not the rms phase [cf Crain et al, 1979][Fremouw et al, 1978].…”

mentioning

confidence: 99%

Numerical computations for a one‐dimensional power law phase screen

Rino¹

1980

Radio Science

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In this paper, numerical computations of the intensity spectral density function of a wave field scattered by a one‐dimensional, power law phase screen are presented. The computations verify theoretically derived asymptotic results showing that when the power law index is greater than three, the scintillation index saturates at a value larger than unity. Moreover, strong focusing, a local maximum in the scintillation index variation with increasing perturbation strength, only occurs in a one‐dimensional medium when the spectral index is greater than or equal to 3. The application of these results to the interpretation of radiowave scintillation data is discussed.

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Use of refractive scattering to explain SHF scintillations

Cited by 28 publications

References 28 publications

Model computations of radio wave scintillation caused by equatorial ionospheric bubbles

Model computations of radio wave scintillation caused by equatorial ionospheric bubbles

Parametrization of spectra of plasma bubble induced VHF satellite scintillations and its geophysical significance

Numerical computations for a one‐dimensional power law phase screen

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