A mobile differential absorption lidar for simultaneous observations of tropospheric and stratospheric ozone over Tibet

We developed a mobile ozone differential absorption lidar system to simultaneously measure the vertical profiles of tropospheric and stratospheric ozone from an altitude of ~5 to 50 km. The system emits four laser beams at wavelength of 289 nm, 299 nm, 308 nm and 355 nm and receives their corresponding Mie/Rayleigh backscattering return signals, and two N₂ Raman return signals at 332 nm and 387 nm shifted from 308 nm and 355 nm, respectively. An assembled telescope array with four 1.25-m telescopes (effective diameter > 2 m) collects the Rayleigh and Raman backscattering signals at 308/332 and 355/387 nm. This system is currently deployed at the Yangbajing Observatory in Tibet (~4300 m elevation) and has begun observations in regular campaign mode since October 2017. The lidar results agree very well with those observed by the Aura/MLS satellite. This novel ozone lidar system operates at the highest elevation of any such system in the world. The higher elevation and larger receiver aperture of this system yield a higher signal-to-noise ratio and lower statistical uncertainty.

Stratospheric temperature monitoring using a vibrational Raman lidar : Part 1: aerosols and ozone interferences

Lidar measurements of temperature for the upper troposphere and lower stratosphere are commonly derived by the Raman technique. Lidar signals derived from vibrational Raman processes have been subjected to numerous simulation tests to examine their sensitivity to the presence of aerosols and ozone in the atmosphere. The influence of aerosols characteristics (wavelength dependence of aerosol extinction and particle phase function) and of ozone concentration on Raman temperature profiles is estimated. Simulations indicate large temperature deviations for post-volcanic conditions. For a Raman backscatter at 607 nm, bias is below 1 K for a total optical depth less than 9 x 10(-3) in the case of a stratospheric contamination and less than 6 x 10(-3) for a tropospheric contamination. The effect of aerosols depends on phase function and a few parameters such as altitude, optical depth and the shape of the high-altitude cloud. The wavelength dependence of aerosol extinction has some influence only for severe post-volcanic conditions (Scattering Ratio, SR >2). For a Raman backscatter at 387 nm, bias is larger and can be significant even in background aerosol conditions. Changes in the ozone density profile lead to significant Raman temperature deviations only for some specific conditions. Results suggest that both aerosol and ozone corrections are necessary to obtain an accuracy better than the 1 K requested for most atmospheric applications.

Redesign and improved performance of the tropospheric ozone lidar at the Jet Propulsion Laboratory Table Mountain Facility

Improvements to the tropospheric ozone lidar at the Jet Propulsion Laboratory Table Mountain Facility for measurements of ozone profiles in the troposphere and lower stratosphere, between approximately 5-and 20-km altitude, are described. The changes were primarily related to the receiver optical subsystems and the data-acquisition system. The original 40-cm Cassegrain telescope was replaced with a faster (f/3) 91-cm Newtonian mirror. In the focal plane of this mirror, the lidar signal is divided into two parts by use of two separate optical fibers as field stops corresponding to different but neighboring 0.6-mrad fields of view. We then separate the two received wavelengths by aligning each transmitted beam to one of the fibers. In addition, two 50-mm telescopes are used for the collection of near-range returns. The four optical signals are brought to a chopper wheel for independent signal selection in the time and range domain. For each channel, an interference filter is used for skylight rejection and additional cross-talk prevention. The signals are detected with miniature photomultiplier tubes and input to a fast photon-counting system. The goals of these modifications were to increase the spatial and temporal resolution of the lidar, to extend the altitude range covered, to improve the quality of the raw data, and to enable regular and routine operation of the system for long-term measurements.