Showing papers on "Scintillometer published in 1981"

Clear weather meteorological effects on propagation at frequencies above 1 GHz

Abstract: This paper reviews the various effects the clear atmosphere may have on the propagation of radio waves above 1 GHz. The role of the transfer processes at the lower boundary of the atmosphere in modifying the refractive index structure of air masses is reviewed, and some results of modification of refractive index and its structure constant by the lower boundary are shown. The formation of various classes of elevated layers is discussed and examples are shown of subsidence layer formation. The formation of refractive structures capping the convective boundary layer is discussed and examples of monsoonal refractive layers are shown. Examples of refractive index gradients and structure constant distributions in the neighborhood of frontal interfaces are also shown and discussed.

Optical wave phase fluctuations.

Abstract: This paper presents a series of studies on the effect of low-frequency fluctuations of the atmospheric refractive index on phase fluctuations of space-limited optical beams. Theoretical calculations have been made in the approximation of a smooth perturbation method. Numerous experimental data on statistical characteristics of optical wave phase fluctuations are given. These are used to verify the theoretical conclusions and to solve an inverse problem on the determination of the atmospheric turbulence characteristics.

Contribution of water vapor monomer resonances to fluctuations of refraction and absorption for submillimeter through centimeter wavelengths

Abstract: Atmospheric fluctuations in temperature, humidity, and total pressure cause fluctuations in the absorption and refraction of electromagnetic waves We consider only the absorption and refraction fluctuations caused by variations in the width and strength of water monomer resonances We differentiate the absorption coefficient and refractive index with respect to temperature, humidity, and total pressure in order to obtain the coefficients that relate the fluctuations in absorption and refraction to these atmospheric parameters The resulting coefficients as well as the absorption coefficient and the refractivity are calculated by summing over all water vapor infrared resonances and are displayed graphically In the limit of low frequencies, these calculated coefficients are in good agreement with the formula for radio wave refractive index The effects of turbulent fluctuations in total pressure are usually negligible

An Optical Device For Path-Averaged Measurements Of C n 2

Abstract: The refractive index structure parameter (Cn2), a statistical measure of refractive index fluctuation in the atmosphere, is useful in predicting the intensity of atmospheric effects upon optical propagation. It can be derived from point measurements of high-speed temperature probes, but in many cases it is better to have a path-averaged measurement. Earlier optical techniques needed corrections for the inner scale of turbulence and were severely limited by the saturation of scintillation. This paper discusses an optical system developed at NOAA that is free of these problems, and makes path-averaged measurements of Cn2 over path lengths from 100 to 500 meters.© (1981) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Reduction of fluctuations of the laser beam intensity by defocusing with an extended lens

Abstract: A method is suggested for calculating fluctuations of the intensity of light propagating in a turbulent medium whose average refractive index is a quadratic function of the transverse coordinates. This method is suitable for the calculation of changes of fluctuations due to thermal defocusing of a beam.