Scholarship & Research
Permanent URI for this communityhttps://scholarworks.montana.edu/handle/1/1
Browse
2 results
Search Results
Item Two wavelength Lidar instrument for atmospheric aerosol study(Montana State University - Bozeman, College of Engineering, 2008) Hoffman, David Swick; Chairperson, Graduate Committee: Kevin S. RepaskyA 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.Item Confocal Fabry-Perot interferometer based high spectral resolution LIDAR(Montana State University - Bozeman, College of Engineering, 2012) Hoffman, David Swick; Chairperson, Graduate Committee: Kevin S. Repasky.A high spectral resolution lidar (HSRL), which has been developed at Montana State University, utilizes a confocal Fabry-Perot interferometer (CFP) to separate aerosol and molecular lidar returns for the purpose of atmospheric aerosol observation. The CFP is actively frequency locked to the laser-transmitter via a novel frequency modulation based technique. 532 nm second harmonic light from a frequency doubled Nd:YAG injectionseeded, pulsed laser is directed vertically into the atmosphere. Light backscattered by the atmosphere is collected using a commercial Schmidt-Cassegrain telescope. The secondharmonic return signal is mode matched into a tunable CFP interferometer with a free spectral range of 7.5 GHz and a finesse of 50.7 (312) at 532 nm (1064 nm) placed in the optical receiver for spectrally filtering the molecular and aerosol return signals. The light transmitted through the CFP is used to monitor the aerosol return signal while the light reflected by the CFP is used to monitor the molecular return signal. Data collected with the HSRL are presented and inversion results are compared to those from a co-located solar radiometer, demonstrating the successful operation of the instrument. The HSRL presented in this dissertation provides an important means to study atmospheric aerosols, which are the largest source of uncertainty in current global climate models. Additionally, the novel frequency locking technique allows for the future development of multi-wavelength HSRL instruments, and the robustness of the frequency locked optical filter allows for the deployment of future air and space based HSRL instruments.