Mueller matrix for atmospheric aerosols at CO2 laser wavelengths from polarized backscattering lidar measurements

The Mueller matrix for atmospheric aerosol backscattering in Utah (a desert environment) is derived from lidar‐polarized backscattering measurements at CO2 wavelengths for a horizontal path a few meters above the ground. The Mueller matrix is nearly a diagonal matrix, with m11 = S11, m22 = (S22 − S33)/2, and m33 ≅ −m22, as is expected for randomly oriented aerosols with axial symmetry. The ratio m22/m11 is approximately 0.75, for which the linear depolarization ratio is approximately 0.15. In computing the Mueller matrix from lidar‐polarized backscattering measurements of various combinations of transmit/receive polarizations (xy), two steps are employed: (1) a deconvolution process to produce a lidar signal pxy(r) from the polarized lidar measurements by deconvolving the long CO2 laser pulse and the lidar system impulse‐response function (i.e., removing their smearing effect from the measured lidar signal), and (2) a constrained slope method to produce an aerosol backscattering coefficient βxy, for each polarization configuration xy, from which the Mueller matrix is computed.