Scintillations due to a concentrated layer with a power‐law turbulence spectrum

Abstract

The spatial spectrum of intensity fluctuations due to a concentrated layer of turbulence is derived from the parabolic wave equation. The spectrum of refractive index fluctuations is taken to be an unmodified power law of arbitrary strength, with exponent a, 2 ( a ( 6. For 2 • a ( 4 it is shown that the intensity spectra for a plane wave can be expressed in terms of a single parameter U, which is the Born approximation to m a, the normalized variance of intensity fluctuation. For U << 1 the Born approximation applies. The high frequency approximation to the intensity spectrum is the angular spectrum that would result from twice the strength of turbulence. It applies above the spatial frequency Kt or 2•r ,•t/U, whichever is. smaller, where ,• is the frequency at the first null of the Born approximation. For U > 30, it represents essentially all of the intensity fluctuations and shows that m saturates at unity for a plane wave as U .--• •o. Simple formulas for m when the source has finite angular extent show that m decreases with increasing turbulence as Ua-a for U >> 1. These results are confirmed by exact calculations for the case a = 3 and by extensive observations of interplanetary scintillations. DUE TO A CONCENTRATED LAYER 113

Latitudinal and temporal variation of equatorial ionospheric irregularities determined from GPS scintillation observations

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Scintillation-induced variability in radio absorption spectra against extragalactic sources

“…This assumption is commonly used in astrophysical situations (Prokhorov et al 1975;Rumsey 1975;Mercier 1962;Salpeter 1967), and a treatment incorporating the extended nature of the scattering medium introduces no additional effects relevant to the present discussion.…”

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“…(4) needs to be modified to take into account both the angular structure of the extragalactic source and its foreground absorbing structure. The power spectrum of intensity fluctuations across the observer's plane is the product of the point source scintillation spectrum with the power spectrum of the source angular brightness distribution (Little & Hewish 1966;Salpeter 1967;Rumsey 1975):…”

Power Spectral Studies of VHF Scintillations Over Near Equatorial Station Anantapur

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