A High Spectral Resolution Lidar at 532 nm for simultaneous measurement of atmospheric state and aerosol profiles using iodine vapor filters

This dissertation presents a High Spectral Resolution Lidar (HSRL) to simultaneously measure vertical profiles of atmospheric temperature, pressure, aerosol to molecular backscatter ratio, and aerosol extinction coefficient. The lidar uses a narrow band pulsed laser source operated at 532 nm and iodine vapor filters are used as narrowband notch filters in the detection system to spectrally separate the Doppler broadened Rayleigh-Brillouin (molecular) scattering and the much less Doppler broadened Mie (aerosol) scattering, thus allowing the spectral lineshape of the molecular scattering to be determined. A total scattering channel that includes both the Mie and Rayleigh-Brillouin scattering is also measured to determine aerosol backscatter ratio simultaneously. Ideally the inversion method requires a pressure at one altitude as the only necessary independent input, along with the assumption of local thermal and hydrostatic equilibrium, and the ideal gas law. For the present HSRL system, a reference temperature at one altitude and time is used to determine a constant normalization factor needed for accurate temperature profiles. This reference temperature is obtained from local balloon soundings for the results presented.; This dissertation describes the iodine vapor filters, the laser transmitter, and the receiver setups and characteristics of the HSRL. The system uses an injection seeded pulsed Nd:YAG laser that is continuously tunable over frequency ranges of 12 GHz and is narrowband, 74 MHz FWHM. The pulsed laser can be locked to an absolute frequency using Doppler-free saturated absorption spectroscopy. The iodine filters are temperature controlled and provide greater than 39 dB rejection of the aerosol backscatter signal with sensitivity in the measured signal to air temperature of 0.4%/K.; A unique feature of the system is the use of a relatively modest size transmitter and receiver system, yet it provides temperature profiles over a range of 500 m up to 15 km, with photon counting errors contributing less than 1 K and an estimated measurement precision of 1.9 K at 1 km. With the lidar data normalized using a reference temperature at one altitude and time from a local balloon sounding, the HSRL has demonstrated RMS deviations in the temperature measurements from the balloon soundings of 1.5 to 2.0 K over an altitude range of 2–5 km for one hour and 300 m averaged temperature profiles. The temperature uncertainty in the lidar measurements is mostly attributed to a 0.7% RMS variation in the photomultiplier tubes and is not an intrinsic source of error in the lidar system. The data presented are compared to local balloon data and show that the lapse rates, tropopause altitudes, and temperature inversions are in good agreement. Several nights of data are presented to demonstrate the salient features of this lidar system and to assess the accuracy of the measurements.