Remote Sensing of Atmospheric Winds Using a Coherent , Cw Lidar _ Nd Speckle - Turbulence Interaction

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. A continuous wave (cw) laser transmitter of modest power level (a watt or two) in conjunction with optical heterodyne detection has been used to exploit the speckle-turbulence interaction and measure the crosswind. The use of a cw transmitter at 10.6 microns and optical heterodyne detection has manyadvantages over direct detection and a double pulsed source in the visible or near infrared. These advantages include the availability of compact, reliable and inexpensive transmitters; better penetration of smoke, dust and fog; stable output power; low 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. From previous work, the time lagged covariance (TCL) function using the joint Gaussian assumption is given for the focused case by (1) = <1> 2 exp [ p2 32 2a 2 3p s/3 0 o i ] f I(l-w)P-_IS/3 dw (2) o where _I and _2 desi$nate_the location of two detectors in the receiver plane; P = P2 PI; T = t2 tl; a = Transmitter Beam Radius; p = Transverse Phase Coherence Length; V = Vector O 181 https://ntrs.nasa.gov/search.jsp?R=19870000896 2018-02-10T08:32:12+00:00Z