Self-consistent Method for Determining Vertical Profiles of Aerosol and Atmospheric Properties Using a High Spectral Resolution Rayleigh-Mie Lidar

Abstract

A self-consistent method of inverting high spectral resolution, Rayleigh-Mie lidar signals to obtain profiles of atmospheric state variables, as well as aerosol properties, is presented. Assumed are a known air pressure at a reference height, hydrostatic equilibrium, the ideal gas law, and the theoretical temperature and pressure dependence of Rayleigh-Brillouin line shapes. For measurements over several kilometers, variations in the atmospheric pressure must be included in the data analysis. The inversion of the signal is greatly facilitated by making a quadratic expansion of the line shape as a function of atmospheric temperature and pressure that is accurate for temperature ranges of ±30 K and pressure ranges of ±25 kPa around a standard temperature and pressure of 275 K and 76 kPa, respectively. Required measurements are the total lidar signal and signals corresponding to different portions of molecular scattering spectrum. These measurements are made possible by using interference filters and atomic vapor filters, which remove the aerosol contribution. The filters are fully characterized by measuring their transmission functions as a function of frequency. For a typical barium filter such as those considered here, the oven temperature must be controlled to better than 1 K for air temperature determination within 1 K. Specially designed filters will be less sensitive to filter temperature. If the bandwidth of the interference filters used is fairly broad, then the inclusion of rotational Raman scattering is important for accurate lidar inversion. Formulas for determining the vertical profiles of atmospheric temperature, pressure, and density, as well as backscatter ratio, backscatter phase function, extinction ratio, and aerosol extinction coefficient are given and their measurement sensitivities are discussed.