TIME-DEPENDENT ATTENUATOR FOR DYNAMIC-RANGE REDUCTION OF LIDAR SIGNALS

A time-dependent variable attenuator to reduce the dynamic range of li dar signals is introduced. The attenuator consists of a Pockels cell b etween 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 retur ns 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 stati stical error remains below the detection limit of 10(-3). Systematic e rrors in differential absorption lidar (DIAL) measurements are negligi ble for relative wavelength differences between on-line and off-line D elta lambda/lambda < 0.1%. Otherwise it is shown how these can be corr ected. We used the attenuator to adapt the measured range to the heigh ts of interest by increasing the electronic gain or to extend the rang e considerably to lower heights. It is estimated that with this variab le attenuator a height range of 0.2-10 km can be covered with one data -acquisition channel only. (C) 1997 Optical Society of America.