Scintillation of light at two colors

Simultaneous measurements were made of the scintillations of red and blue light in the atmosphere. The sources were a He-Ne laser at 633 nm and a He-Cd laser at 422 nm. Several horizontal propagation paths were used, and the strength of turbulence and its inner scale were recorded during the experiments. Weak path-integrated turbulence theory predicts a very high correlation between the scintillations at these two wavelengths. We observed that the correlations were lower than this prediction in strong path-integrated turbulence. The weak turbulence theory consists of a double integral that sums contributions from each position along the path and from each turbulent wavenumber. To include the effects of strong turbulence, we assume that the effectiveness of eddies larger than the transverse coherence length of the field at each path position is reduced.</jats:p

Refractive-Index structure parameter profiling system

The line-averaged refractive-index structure parameter C n 2 can be measured conveniently by observing the irradiance fluctuations of an incoherent light source with a receiver, where both the transmitter and receiver apertures are the same diameter and large compared to a Fresnel zone.1The measurement is most sensitive to C n 2 in the center of the path, tapering to zero weight at the ends of the path. The incoherent apertures form broad spatial filters that have a peak response to refractive-index irregularities having a spatial wavelength slightly larger than the aperture diameter. The weighting function may be shifted from the center of the path by using different diameter transmitters and receivers and by taking the difference of two transmitting or two receiving aperture signals. To avoid the effects of scintillation saturation, however, each individual aperture should be sufficiently large,1which restricts the filter complexity for an instrument of practical size. With these factors in mind, we developed a compact profiling instrument that measures C n 2 on three segments of an optical path between three-element transmitters and receivers.</jats:p

Cross correlations and cross spectra for spaced antenna wind profilers 2. Algorithms to estimate wind and turbulence

International audienc

Optical crosswind profiling system

A wind-profiling system has been developed that uses zero-mean transmitting and receiving filters to shape and analyze the intensity scintillation produced by refractive-index irregularities along the light path. The method is a variation of a technique first proposed by Lee. Two transmitting filters and three pairs of receiving filters are employed, and five of the six combinations are used to form filters in space which are sensitive to refractive-index irregularities, moving across the light path, of a specific spatial wavelength and at a specific location.</jats:p