Dept. of Electrical Engineering
Oregon Graduate Center
Speckle-turbulence interaction can be utilized in single-ended remote sensing of path averaged atmospheric crosswinds. If a laser transmitter is used to illuminate a target, the resultant speckle field generated by the target is randomly perturbed by atmospheric turbulence as it propagate back to the transmitter-receiver. When a crosswind is present, this scintillation pattern will move with time across the field of view of the receiver. As a result, the averaged vector wind velocity along the path perpendicular to the direction of propagation can be obtained by using the time-delayed statistics of the speckle field at the receiver. The theoretical basis of the speckle propagation through the turbulent atmosphere is provided along with the analytical formulations of the time-delayed statistics of the return intensity. Several wind sensing techniques using these statistics are described and their performance evaluated. The turbulence-induced correlation between the outgoing and return paths was considered and the analytical formulations of the dependence effect of the two paths on the time-delayed statistics and the performance of remote measurements of atmospheric parameters using optical heterodyne detection are presented. A continuous wave laser transmitter of modest power in conjunction with optical heterodyne detection can exploit the speckle-turbulence interaction to measure the crosswinds. Several optical heterodyne transmitter-receiver systems, using a CO2 waveguide laser as the source, were designed and built. The major difficulty to design an optical heterodyne system is to obtain sufficient optical isolation between the transmitter and local oscillator beams. The novel techniques developed to improve the isolation are described. It was also shown that an optimum local oscillator level exists when photoconductors are used as optical heterodyne detectors. Considerable amount of data were obtained over three different target ranges of 500m, 1000m and 1300m. The experimental data taken under different atmospheric conditions are represented and discussed. An analysis was performed to predict the measurement errors associated with the statistical parameters required to determine the wind velocity. Then, the optimum system parameters for which the estimation of wind velocity is most accurate were obtained.
Amzajerdian, Farzin, "Remote sensing of atmospheric winds by utilizing speckle-turbulence interaction and optical heterodyne detection" (1988). Scholar Archive. 267.