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Separation of Equation 21 into Equations 23 and 24 allows solution of various atmospheric properties. Given a well mixed atmosphere, one can deduce the molecular backscatter cross-section per unit volume, , (Piironen, 1994)
at the laser wavelength of 532 nm. A local radiosonde yields the vertical temperature and pressure profiles. Knowledge of the molecular backscatter cross-section per unit volume as a function of range thus provides a calibration target for the lidar.
Substitution of into Equation 23 for two atmospheric levels, and , yields the optical depth of that layer at the lidar wavelength,
The scattering ratio, aerosol to molecular signal, is defined as
Using this definition and taking the ratio of Equation 24 to Equation 23, the aerosol backscatter cross-section can be written as
Figure 7 illustrates the HSRL measured aerosol and molecular backscattered return as a function of altitude (lower plot). The column integrated visible optical depth (upper plot) is due to aerosol attenuation of the molecular signal, determined from Equation 26. Aerosol backscatter, represented by the dashed curve, increases with cloudcover (5.5 to 7.5 km) and haze (3.5 to 5 km).
Figure 7: Upper plot illustrates HSRL measured column integrated visible optical depth relative to inverted aerosol (dashed line) and molecular (solid line) backscatter returns shown in the lower plot.
Backscatter depolarization is monitored to discriminate between spherical and
non-spherical particles. Spherical particles (e.g., liquid,
water-vapor laden solids) backscatter photons with a small change in
the polarization. However, non-spherical particles (e.g., ice crystals, dust)
backscatter light with a large change in polarization. Range
resolved depolarization provides analysis of cloud phase and
discriminates between spherical and non-spherical aerosols.