HSRL SOCRATES data processing

GV-HSRL makes four range-resolved backscatter observations:

(i) combined_hi - High receiver efficiency observation of parallel polarized total backscatter (clouds, aerosols, and molecules).  Analogous to an elastic backscatter signal.
(ii) combined_lo - low receiver efficiency observation of parallel polarized total backscatter (clouds, aerosols, and molecules).  Analogous to an elastic backscatter signal.
(iii) molecular - Molecular only parallel polarized backscatter channel.  Aerosol and cloud signals are blocked using an iodine absorption filter which blocks the spectrally narrow particulate backscatter but passes the wings of the spectrally broad molecular backscatter.
(iv) cross - The cross-polarized total backscatter channel.  HSRL transmits and receives circularly polarized light.

The primary data products of the GV-HSRL are:

Aerosol_Backscatter_Coefficient - Optical property of the scattering volume describing how strongly it scatters light at a 180 degree scattering angle. It is obtained through the relative ratio of total backscatter to molecular backscatter (B) then multiplying by the expected molecular backscatter coefficient (based on estimated temperature and pressure profiles).

Particle_Linear_Depolarization_Ratio - The tendency for particles in the scattering volume to reduce the degree of polarization of incident light upon backscattering. This is generally an indicator for asphericity of particles (da) This data product has molecular scattering effects removed. The linear depolarization ratio uses the volume_depolarization (obtained using combined parallel and cross-polarized returns) and the Backscatter_Ratio (the ratio of total to molecular scattering).

Optical_Depth - One-way optical depth measured from the lidar to the volume. Optical depth is the exponent of the atmospheric transmission to the scattering volume, and therefore an accumulation of extinction in each point up to the scattering volume. It is derived from the observed molecular backscatter (Nm) relative to the expected molecular backscatter coefficient.

Aerosol_Extinction_Coefficient - The optical property describing the tendency of the volume to extinguish light by either scattering it or absorbing it. Extinction is the range derivative of the optical depth.

Other variable definitions used for the derived data products:

Volume depolarization - The propensity of the observation volume to depolarize including both aerosol and molecular contributions. The concept of “depolarization” in contrast to “depolarization ratio” is discussed in Gimmestad (2008).

Backscatter_Ratio - the ratio of all scattering particles to only molecular scattering.  This quantity is polarization independent.

Particle_Depolarization - depolarization resulting from only particulate scatterers.  The molecular contribution is removed.