Inversion of Planetary Boundary Layer Height with a Laser Diode Ceilometer Using an Improved Gradient Algorithm
C-W. Yang, W-Q. Liu and Y-J. Zhang
Determination of planetary boundary layer (PBL) height is a very important applications for laser diode ceilometer. Since the backscatter signal which is contaminated seriously by noise has greater fluctuation and signal-to-noise-ratio (SNR) is lower, the inversion of the PBL height using a classic gradient method directly will produce very large deviations. This paper presents a improved gradient method, At first, in order to eliminate the inversion deviations of PBL height which is caused by the larger fluctuations of long-distance backscatter signal, a kind of SNR estimation methods is described in detail. Some constraints just like SNR are used to limit the effective vertical range of the PBL inversion. Next, the backscatter signals within the vertical range are averaged in time and smoothed in distance, so as to eliminate smallscale features that may lead to faulty PBL height detections. At last, a gradient method that is more suitable to calculate discrete point is used to retrieve the PBL height. The experimental results indicate that the method is more stable and reliable in detecting PBL height and has a great practical value for laser diode ceilometer.
Keywords: Atmospheric optics, planetary boundary layer (PBL), boundary layer height, laser diode, ceilometer, improved gradient algorithm