Scintillation

About: Scintillation is a research topic. Over the lifetime, 14022 publications have been published within this topic receiving 187694 citations.

Improved amplitude- and phase-scintillation indices derived from wavelet detrended high-latitude GPS data

Abstract: Accuracy and validity of scintillation indices estimated using the power and phase of the GPS signal depend heavily on the detrending method used and the selection of the cutoff frequency of the associated filter. A Butterworth filter with a constant cutoff frequency of 0.1 Hz is commonly used in detrending GPS data. In this study, the performance of this commonly used filter is evaluated and compared with a new wavelet-based detrending method using GPS data from high latitudes. It was observed that in detrending high-latitude GPS data, a wavelet filter performed better than Butterworth filters as the correlation between amplitude- and phase-scintillation indices in S 4 and ? ? improved significantly from 0.53, when using a Butterworth filter, to 0.79, when using the wavelet filtering method. We also introduced an improved phase-scintillation index, ? CHAIN, which we think is comparatively a better parameter to represent phase scintillations at high latitudes as the correlation between S 4 and ? CHAIN was as high as 0.90. During the analysis, we also noted that the occurrence of the "phase scintillation without amplitude scintillation" phenomenon was significantly reduced when scintillation indices were derived using the wavelet-based detrending method. These results seem to indicate that wavelet-based detrending is better suited for GPS scintillation signals and also that ? CHAIN is a better parameter for representing GPS phase scintillations at high latitudes.

Nonlinear least-squares modeling of 3D interaction position in a monolithic scintillator block.

Abstract: This paper presents a study of possible models to describe the relation between the scintillation light point-of-origin and the measured photo detector pixel signals in monolithic scintillation crystals From these models the X, Y and depth of interaction (DOI) coordinates can be estimated simultaneously by nonlinear least-square fitting The method depends only on the information embedded in the signals of individual events, and therefore does not need any prior position training or calibration Three possible distributions of the light sources were evaluated: an exact solid-angle-based distribution, an approximate solid-angle distribution and an extended approximate solid-angle-based distribution which includes internal reflection at side and bottom surfaces The performance of the general model using these three distributions was studied using Monte Carlo simulated data of a 20 × 20 × 10 mm lutetium oxyorthosilicate (Lu2SiO5 or LSO) block read out by 2 Hamamatsu S8550 avalanche photo diode arrays The approximate solid-angle-based model had the best compromise between resolution and simplicity This model was also evaluated using experimental data by positioning a narrow 12 mm full width at half maximum (FWHM) beam of 511 keV photons at known positions on the 20 × 20 × 10 mm LSO block An average intrinsic resolution in the X-direction of 14 mm FWHM was obtained for positions covering the complete block The intrinsic DOI resolution was estimated at 26 mm FWHM

Refractive Scintillation in the Interstellar Medium

Abstract: It is shown here that the large-scale component of interstellar scintillation which causes the slow variation in the apparent intensity of pulsars on time scales of days to months can be greatly enhanced when the turbulence spectrum has a limiting inner scale of the order 10 to the 9th m. This solution is extended to the spherical diverging geometry appropriate for a pulsar embedded in the ISM, and a similar enhancement is found. A comparison of this solution with pulsar observations is used to place bounds on the inner scale of the ISM. 39 references.

Refractive and diffractive scattering in the interstellar medium

Abstract: Radio wave propagation through electron-density fluctuations in the ISM is studied. Observable propagation effects are explored using a one-dimensional thin-screen model for the turbulent medium. Diffraction caused by stochastic small-scale irregularities is combined with refraction from deterministic large-scale irregularities. Some of the effects are illustrated with numerical simulations of the wave propagation. Multiple imaging is considered, delineating the possible effects and discussing their extensions to two-dimensional screens and extended three-dimensional media. The case where refraction as well as diffraction is caused by a stochastic medium with a spectrum of a given form is considered. The magnitudes of observable effects is estimated for representative spectra that may be relevant to the ISM. The importance of the various effects for timing and scintillation observations of pulsars, VLBI observations of galactic and extragalactic radio sources, and for variability measurements of extragalactic sources is assessed. 47 references.

Coordinated study of equatorial scintillation and in situ and radar observations of nighttime F region irregularities

Abstract: A coordinated set of Atmospheric Explorer E (AE-E) satellite in situ, VHF radar backscatter, and scintillation measurements performed during 1977 over a common ionospheric volume is used to study the relationship between the plasma depletions or bubbles, the extended 3-m irregularity structures known as plumes, and bursts of scintillation activity or patches in the nighttime equatorial F region. The implications of the observed spatial structures and the level of ambient concentration on the generation of 3-m irregularities and scintillation modeling are discussed.