Limitations of Signal Averaging of Dial Measurements Due to Temporal Correlation*

Abstract

The accuracy of the remote sensing of species in the atmosphere using a differential-absorption LIDAR (DIAL) system is dependent upon the determination of the value of the "on-resonance" DIAL return compared to the "off-resonance" value. The accuracy of such measurements can generally be improved by increasing the number of measurements and taking average values. This paper describes the results of an experiment which directly measured the effect of averaging on the measurement uncertainty, where the uncertainty is defined by the standard deviation of the mean value of the returns. Our results show that the reduction of the standard deviation by signal averaging over increasing numbers of pulses is much smaller than would be anticipated for independent measurements and is due to small but long-term temporal correlation. The results are shown to be in excellent agreement with a theoretical analysis which takes the correlation of successive LIDAR returns into account.