Abstract

A time-dependent variable attenuator to reduce the dynamic range of lidar signals is introduced. The attenuator consists of a Pockels cell between two crossed polarizers that is incorporated into the receiving optic. The transmission is controlled electronically to attenuate the large signals from close ranges but to transmit far-range signal returns to their full extent. The signal dynamic range has been reduced by more than a factor of 100. Reproducibility and the effect of different rise times on the variable transmission are investigated. It is found that the attenuation is highly reproducible, and the associated statistical error remains below the detection limit of 10^-3. Systematic errors in differential absorption lidar (DIAL) measurements are negligible for relative wavelength differences between on-line and off-line Δλ/λ < 0.1%. Otherwise it is shown how these can be corrected. We used the attenuator to adapt the measured range to the heights of interest by increasing the electronic gain or to extend the range considerably to lower heights. It is estimated that with this variable attenuator a height range of 0.2–10 km can be covered with one data-acquisition channel only.

© 1997 Optical Society of America

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