Two wavelength Lidar instrument for atmospheric aerosol study
Hoffman, David Swick
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A two-color lidar instrument and inversion algorithms have been developed for the study of atmospheric aerosols. The two-color lidar laser transmitter is based on the collinear fundamental 1064 nm and second harmonic 532 nm output of a Nd:YAG laser. Scattered light is collected by the two-color lidar receiver using a Schmidt-Cassegrain telescope with the 532 nm channel monitored using a gated photomultiplier tube (PMT) and the 1064 nm channel monitored using an avalanche photodiode (APD). Data is collected from the PMT and APD using a 14 bit 200 MHz data acquisition card. The lidar inversion algorithm developed to analyze the data collected by the two-color lidar is based on a constant lidar ratio assumption at both the 1064 nm and 532 nm wavelengths with the constrained ratio aerosol model (CRAM) providing the initial lidar ratios at the two wavelengths to complete the lidar inversion. Data from the CALIOP lidar on board the CALIPSO satellite are presented to verify software algorithm performance. Data from the two-color lidar are then presented demonstrating the two-color lidar instrument's capabilities. The analysis of these data identifies smoke and industrial aerosols in the atmosphere above Bozeman. Finally an error analysis of the lidar instrument and accompanying analysis software is presented. The findings of this analysis are that error introduced by the APD and PMT is dominant; the error introduced by the optical detectors is much larger than the error from other sources examined such as quantization error, and the error associated the use of numerical integration in the data analysis algorithm.