Noise filtering of Rotational Raman Lidar using threshold amendment for atmospheric temperature measurement

Pure Rotational Raman Lidar is a new technique for detecting vertical troposphere temperature profile. Since the backscattering Raman signals are so weak that the photon-counting method is applied by using a multiscaler. By setting the threshold of the multiscaler, most noises mixed with the signals can be filtered. However, difference exists between the set threshold and the actual threshold of the two count channels, and also exists between the set thresholds of the two count channels. This will affect quick-setting of the appropriate thresholds. In this paper, a rule is put forward and the measuring system is established to confirm the set threshold value corresponding to an actual one, making use of the amplitude fluctuation of square wave. By this system, pairs of set threshold and actual threshold are obtained, and the curve of the set threshold against the actual threshold of a single count channel, as well as the curve of thresholds of the two count channels, is fitted. The theoretical analysis is well agreed with the experimental results, and it indicates that the appropriate threshold can be set more quickly by using the curve.