Abstract

Speckle-turbulence interaction has the potential for allowing single-ended remote sensing of the path averaged vector crosswind in a plane perpendicular to the line of sight to a target. If a laser transmitter is used to illuminate a target, the resultant speckle field generated by the target is randomly perturbed by the atmospheric turbulence as it propagates back to the location of the transmitter-receiver. When a crosswind is present, this scintillation pattern will move with time across the receiver aperture; and consequently, the time-delayed statistics of this turbulence-perturbed speckle field are dependent on the crosswind velocity. A cw laser transmitter of modest power level in conjunction with optical heterodyne detection can be used to exploit the speckle-turbulence interaction and measure the crosswind. The use of a cw transmitter at 10.6 μm and optical heterodyne detection has many advantages over previous work which used direct detection and a double-pulsed source in the near infrared. These advantages include the availability of compact, reliable, and inexpensive transmitters; better penetration of smoke, dust, and fog; stable output power; no beam pointing jitter; and considerably reduced complexity in the receiver electronics. In addition, with a cw transmitter, options exist for processing the received signals for the crosswind that do not require a knowledge of the strength of turbulence. Analytical and experimental results are presented.

© 1985 Optical Society of America