Theory of refractive scattering in scintillation phenomena

Booker, Henry G.; Majidiahi, Gholamreza

doi:10.1016/0021-9169(81)90035-0

Cited by 74 publications

(70 citation statements)

References 23 publications

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“…Again, this is to be contrasted to <A02>' / 2 < I, where we found the spatial period of the amplitude variation is D. Now consider a sinusoidal phase screen at Z = 0 and a reception plane at some distance Z for which the Fresnel zone size is F. Let <A02>1 / >> I and D >> F. For these conditions, we are concerned with the lens-like refractive scattering (Booker, MajidiAhi, 1981) described above. Such a screen will produce foci in a plane parallel to the screen.…”

Section: W(x) F W(s) Eikxsdsmentioning

confidence: 98%

“…7 shows that in going from a one-dimensional sinusoidal phase screen to an irregular power law screen with spectral index 4, the fine structure, or focal scale, is determined by replacing the sinusoidal wavelength by the outer scale of irregularities (Booker, MajidiAhi, 1981). Booker and Tao (1987) have shown that for a one-dimensional phase screen with spectral index I < p < 3, Eq.…”

Section: )mentioning

confidence: 99%

“…Note that the spectra in this case extend to high normalized frequencies, corresponding to the fine scale structure produced under these conditions. Using the theory outlined above for the deeply modulated phase screen, Booker and MajidiAhi (1981) have generated the intensity spectra shown in Fig. 4.…”

Section: )mentioning

confidence: 99%

“…Another much simpler method is the multiple refractive scatter model developed by Booker (Booker, MajidiAhi, 1981). In this method, the multiple-scattering region is replaced by a single "deeply modulated" phase-changing screen.…”

Section: Introductionmentioning

confidence: 99%

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Effects of Strong Scattering on Transionospheric Propagation

Sprague¹

1989

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A JAN12 1990Appro~d for pUbic releas; Cstrbtln is wianited. Approved for public release; distribution is unlimited. 01 12 072 NAVAL OCEAN SYSTEMS CENTER ABSTRACT PWl&mn 200 w ds). .This report presents preliminary results of an effort to model the effects of ionospheric electron density irregularities on transionospheric propagation. The focus of the report is on propagation at HF and low VHF, where strong multiple scattering is often encountered. A strong scattering model is therefore used to predict the effects on such parameters as the phase autocorrelation function, the spectrum of intensity fluctuations, and the fluctuation in angle of arrival. Reqrements for improvements in the model and directions for later work are discussed. PREFACEThis report presents the results of modeling the effects of electron density irregularities on transionospheric propagation. The objective of this effort has been to provide a tool for determining, in real time, the expected effects of such irregularities on the performance of a given transionospheric monitoring system. While these effects can take several forms, we concentrate here on the -ariation in the phase of the signal due to scattering caused by such irregularities.In this report, we shall be mainly interested in remote locating systems. Such systems rely on accurate measurements of the phase difference between separated receive antennas to provide estimates of apparent angular location (azimuth/ elevation). Fluctuations in this phase difference due to scattering caused by electron density irregularities result in a consequent fluctuation in the apparent location of the transmitter. System performance can be seriously degraded if the correlation in the phase fluctuation between antennas is low or the mean square fluctuation in phase is large. In any case, the accurate determination of the phase fluctuations provides an estimate of the error for a given location estimate and thus provides important information for the system user.Another feature that must be addressed under strong multiple-scattering conditions is the reduction of correlation in the intensity of the signal. Under such scattering conditions, defocusing by large scale* irregularities can cause deep small-period fades in signal strength. For sufficiently strong scattering, these signal fades may have a spatial extent on the order of the size of the locating system (tens of meters). This loss of signal makes the system unreliable at best and, in some cases, inoperable.This area of investigation is not completely new; there exists a large body of related work. What is different about this effort is the extension to low VHF and HF operational frequencies. Previous work has, for the most part, dealt with higher frequencies where, in general, the relatively simple single-scatter models are applicable. Also, at these frequencies, one can generally ignore the refractive effects of the background ionization. This simplifies the implementation of the models considerably.At lower frequencies, strong multiple refra...

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Section: W(x) F W(s) Eikxsdsmentioning

confidence: 98%

Section: )mentioning

confidence: 99%

Section: )mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Effects of Strong Scattering on Transionospheric Propagation

Sprague¹

1989

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“…However, it has also been suggested that larger scales corresponding to the typical scale size in the ionosphere can also contribute as they may be associated with amplitudes of phase variation as high as hundreds to thousands of radians (Booker and Majidiahi, 1981). In this case, the irregularity acts as a refracting media and the interference of the refracted waves on the ground produce the spatial pattern whose movement causes scintillations in a fixed location radio wave record.…”

Section: Introductionmentioning

confidence: 99%

Low frequency modulation of transionospheric radio wave amplitude at low-latitudes: possible role of field line oscillations

et al. 2002

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Abstract. Ionospheric scintillations of radio waves at lowlatitudes are associated with electron density irregularities. These irregularities are field-aligned and can provide excitation energy all along the field line to non-local field-aligned oscillations, such as the local field line oscillations. Eigenperiods of toroidal field line oscillations at low-latitudes, computed by using the dipole magnetic field and ion distributions obtained from the International Reference Ionosphere (IRI) for typical nighttime conditions, fall in the range of 20-25 s. When subjected to spectral analysis, signal strength of the radio waves recorded on the 250 MHz beacon at Pondicherry (4.5 • N dip), Mumbai (13.4 • N dip) and Ujjain (18.6 • N dip) exhibit periodicities in the same range. For the single event for which simultaneous ground magnetic data were available, the geomagnetic field also oscillated at the same periodicity. The systematic presence of a significant peak in the 20-25 s range during periods of strong radio wave scintillations, and its absence otherwise suggests the possibility that field line oscillations are endogenously excited by the irregularities, and the oscillations associated with the excited field line generate the modulation characteristics of the radio waves received on the ground. The frequency of modulation is found to be much lower than the characteristic frequencies that define the main body of scintillations, and they probably correspond to scales that are much larger than the typical Fresnel scale. It is possible that the refractive mechanism associated with larger scale long-lived irregularities could be responsible for the observed phenomenon. Results of a preliminary numerical experiment that uses a sinusoidal phase irregularity in the ionosphere as a refracting media are presented. The results show that phase variations which are large enough to produce a focal plane close to the ground can reproduce features that are not inconsistent with our observations.

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Study of equatorial E region irregularities using rare daytime VHF scintillation observations

Yadav¹,

Kakad²,

Pant

et al. 2015

JGR Space Physics

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Scintillations on VHF radio signal are sparsely observed during daytime due to unavailability of strong electron density irregularities in equatorial E or F region. Type I/II irregularities observed at E region altitudes during the daytime are linked with either two‐stream or gradient drift instability. The occurrence of these irregularities in presence of strong blanketing Es (Esb) can produce weak‐moderate scintillations on VHF signal during daytime. Such sparse daytime VHF scintillations are used in the present study to retrieve information about E region irregularities, which are generally examined with radar observations. We use spaced receiver scintillation observations on 251 MHz signal transmitted from geostationary satellite UFO2 (71.2°E) and recorded at Tirunelveli (8.5°N, 77.8°E, dip latitude 0.6°N). Ionosonde data from Trivandrum (8.5°N, 76.6°E, dip latitude 0.5°N) during 2003–2005 is used to confirm the association of daytime scintillations with Esb. The daytime scintillations last for 15–45 min during postnoon hours. Their occurrence closely matches the peak occurrence time of Esb. For the first time, spatial scale lengths of E region irregularities are obtained using the technique introduced by Bhattacharyya et al. (2003). The observed spatial scales are validated using theoretical model. The theoretical model manifests 6–19% density fluctuations in the E region to produce weak scintillations (0.15 ≤S4≤ 0.4) on 251 MHz. The study reveals that scale lengths of E region irregularities are smaller on counter equatorial electrojet (CEEJ) days than non‐CEEJ days, which could be resulting from lower electron temperatures in E region on CEEJ days.

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Theory of refractive scattering in scintillation phenomena

Cited by 74 publications

References 23 publications

Effects of Strong Scattering on Transionospheric Propagation

Effects of Strong Scattering on Transionospheric Propagation

Low frequency modulation of transionospheric radio wave amplitude at low-latitudes: possible role of field line oscillations

Study of equatorial E region irregularities using rare daytime VHF scintillation observations

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