Laser speckle effects on hard target differential absorption lidar

Edward P. MacKerrow; Joseph J. Tiee; Charles B. Fite; Mark J. Schmitt; Michael C. Whitehead; Robert J. Nemzek; George E. Busch; Charles Robert Quick Jr.; Dennis K. Remelius; Patrick Schafstall; David C. Thompson

doi:10.1117/12.236904

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29 March 1996 Laser speckle effects on hard target differential absorption lidar

Edward P. MacKerrow; Joseph J. Tiee; Charles B. Fite; Mark J. Schmitt; Michael C. Whitehead; Robert J. Nemzek; George E. Busch; Charles Robert Quick Jr.; Dennis K. Remelius; Patrick Schafstall; David C. Thompson

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Proceedings Volume 2702, Gas and Chemical Lasers; (1996) https://doi.org/10.1117/12.236904
Event: Photonics West '96, 1996, San Jose, CA, United States

Abstract

Reflection of laser light from a diffuse surface exhibits a complex interference pattern known as laser speckle. Measurement of the reflected intensity from remote targets, common to `hard-target' differential absorption lidar, requires consideration of the statistical properties of the reflected light. We have explored the effects of laser speckle on the noise statistics for CO₂ DIAL. For an ensemble of independent speckle patterns it is predicted that the variance for the measured intensity is inversely proportional to the number of speckle measured. We have used a rotating drum target to obtain a large number of independent speckle and have measured the predicted decrease in the variance after correlations due to system drifts were removed. Measurements have been made using both circular and linear polarized light. These measurements show a slight improvement in return signal statistics when circular polarization is used. We have conducted experiments at close range to isolate speckle phenomena from other phenomena, such as atmospheric turbulence and platform motion thus allowing us to gain a greater understanding of speckle issues. We have also studied how to remove correlation in the data caused by albedo inhomogenuties producing a more statistically independent ensemble of speckle patterns. We find that some types of correlation are difficult to remove from the data.

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Edward P. MacKerrow, Joseph J. Tiee, Charles B. Fite, Mark J. Schmitt, Michael C. Whitehead, Robert J. Nemzek, George E. Busch, Charles Robert Quick Jr., Dennis K. Remelius, Patrick Schafstall, and David C. Thompson "Laser speckle effects on hard target differential absorption lidar", Proc. SPIE 2702, Gas and Chemical Lasers, (29 March 1996); https://doi.org/10.1117/12.236904