Showing papers by "Stanley M. Flatté published in 1994"
TL;DR: In this article, the authors carried out numerical simulations of wave traversing a three-dimensional random medium with Gaussian statistics and a power-law spectrum with inner-scale cutoff and provided the probability density function (PDF) of irradiance.
Abstract: We have carried out numerical simulations of waves traversing a three-dimensional random medium with Gaussian statistics and a power-law spectrum with inner-scale cutoff. The distributions of irradiance on the final observation screen provide the probability-density function (PDF) of irradiance. For both initially plane and initially spherical waves the simulation PDF’s in the strong-fluctuation regime lie between a K distribution and a log-normal-convolved-with-exponential distribution. We introduce a plot of the PDF of scaled log-normal irradiance, on which both the exponential and the lognormal PDF’s are universal curves and on which the PDF at both large and small irradiance is shown in detail. We have simulated a spherical-wave experiment, including aperture averaging, and find agreement between the simulated and the observed PDF’s.
104 citations
TL;DR: In this article, the effects of internal waves can account for the broadband fluctuations, the breakdown of the geometrical optics wavefront pattern and broadening of the wavefront near the transmission finale, and a coherent wavefront motion with a timescale near the semi-diurnal tidal period.
Abstract: A recent 1000‐km acoustic pulse transmission experiment in the Pacific revealed unexpected fluctuations on received wavefronts, including a dominant rapid variation, called the broadband fluctuation, with time scales less than 10 minutes and spatial scales of less than 60 m; a distinct breakdown of the geometrical optics wavefront pattern and broadening of the wavefront near the transmission finale; and a coherent wavefront motion with a timescale near the semi‐diurnal tidal period Parabolic‐equation numerical simulations have been carried out which utilize environmental data and which take into account internal‐wave‐induced sound‐speed perturbations obeying the Garrett–Munk (GM) spectral model It is shown that the effects of internal waves can account for the broadband fluctuations, the breakdown of the geometrical optics pattern, and the wavefront broadening The sensitivity of these fluctuations to internal‐wave energy and modal content is examined The spectral energy in the GM model at tidal period
88 citations
09 Jun 1994
TL;DR: In this article, Bester et al. used the Infrared Spatial Interferometer (IRI) to investigate both Kolmogorov and non-Kolmoggorov models for light passing through the upper atmosphere.
Abstract: Bester et al. report measurements of atmospheric fluctuations made with the Infrared Spatial Interferometer, which indicated behavior not in accord with the standard Kolmogorov model with only a single constant wind velocity. Our numerical simulations use relatively complex models of the atmosphere to investigate both Kolmogorov and non-Kolmogorov models. We find that the measurements of Bester et al. for light passing through the upper atmosphere are within the limits of behavior for Kolmogorov models, but often only if the outer scale of turbulent fluctuations is between 15 to 100 meters. The possibility that the measured behavior might be non-Kolmogorov is not excluded. We also examine measurements made along short paths in the surface boundary layer, where some measurements of Bester et al. showed variations in the atmospheric fluctuations with seeing conditions which appeared to be non-Kolmogorov. These variations can be perhaps be explained by standard models, but require that seeing improve with increasing wind speed in the surface layer. We discuss some other measurements which lend some support to that idea. However, we cannot exclude non-Kolmogorov behavior. We find that meteorological data is needed concurrent with astronomical observations, to help constrain the models. The size of the outer scale, the wind velocity profile and the turbulence spectrum are important to the ultimate capabilities of interferometers and other systems with adaptive optics.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
3 citations
29 Jun 1994
TL;DR: In this article, Bester et al. used a particular observable (slope of the Allan variance) with an infrared interferometer in an attempt to distinguish models for turbulence induced phase fluctuations seen in ground-based telescopes.
Abstract: Questions still exist concerning the appropriate model for turbulence- induced phase fluctuations seen in ground-based telescopes. Bester et al. used a particular observable (slope of the Allan variance) with an infrared interferometer in an attempt to distinguish models. The authors have calculated that observable for Kolmogorov and {open_quotes}random walk{close_quotes} models with a variety of outer scales and altitude-dependent turbulence and wind velocity. The authors have found that clear distinction between models requires good data on the vertical distribution of wind and turbulence. Furthermore, measurements at time separations of order 60 s are necessary to distinguish the {open_quotes}random walk{close_quotes} model from the Kolmogorov model.