Graduation date: 2000

Several horizontal flight segments from SESAME and ALPEX are studied using structure functions and specral analysis methods. Theoretical analysis of the relative errors in structure function and correlation function in the presence of large scale wave activity is presented. The effect of stratification and shear on the -5/3 inertial subrange is noted. The expected ratio of horizontal velocity components for spectra and structure functions (4/3) is observed in the inertial subrange. The observed changes in the aspect ratio (defined as the square root of ratio of vertical velocity structure function to the mean horizontal velocity structure function) with turbulence strength and stratification are analysed. / Graduation date: 1986

Thesis (Ph. D.)--Oregon Graduate Center, 1974.

Thesis (Ph. D.)--Oregon Graduate Center, 1982.

Ph.D. / Applied Physics / Using the extended Huygens Fresnel principle, the effect of the atmospheric turbulence on the statistical properties of a polychromatic speckle field, generated by a diffuse target, is studied in detail. The results, substantiated by experimental data, indicate that the atmospheric perturbation increases the variance of the received intensity substantially and is sensitive to the wavelength, beam size and beam geometry. The results for the covariance of the received intensity, normalized to the variance, indicate that, at low turbulence levels, reduction in vacuum speckle contrast ratio (VSCR) also reduces the normalized covariance but, with further increase in the turbulence level, reduction in the vacuum speckle contrast ratio increases the normalized covariance. Also it is found that for small detector spacings, the normalized covariance remains approximately constant even with substantial increase in the turbulence level. By resolving the time delayed covariance of the received intensity (TDC), into coherent and incoherent terms, it is shown that for large time delays, the time delayed covariance is determined by the incoherent fluctuations and for poor vacuum speckle contrast ratio, the time delayed covariance is not very sensitive to the wind velocity. Finally it is shown that due to the atmospheric perturbation the probability density function of the received intensity changes from an M-distribution or a sum of exponential distributions in vacuum to a K-distribution or a weighted sum of K-distributions in the presence of the turbulent atmosphere.

Thesis--M. Phil., University of Hong Kong, 1984.

published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

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