Backscatter Matrix Observations by The GV-HSRL

Abstract

The GV-HSRL is a high spectral resolution lidar capable of measuring calibrated backscatter, extinction and circular depolarization from the ground or NSF Gulfstream V platform. In the spring of 2012, the instrument was modified to measure the full backscatter matrix of atmospheric scatterers. This modification enabled us to investigate the polarization properties of oriented particles and further understand where particles orient and how they may impact depolarization lidar data. Observations were performed from the ground at different times with the lidar’s tilt angle at 4°, 22° and 32° degrees off zenith. This instrument found oriented ice crystals only produced observable polarization effects at the 32° lidar tilt angle. By contrast, a significant fraction of rain observations have oriented scattering matrices at all three lidar tilt angles. Thus conventional depolarization lidar is generally well suited for characterizing ice crystals but not liquid precipitation. Oriented ice crystals are most commonly investigated by looking for specular scatter from horizontally oriented plates. While this method offers excellent sensitivity to small populations of oriented plats, it has very little capability to determine the fraction of oriented plates if the population is larger than about 1%. We show here that observing f12 scattering matrix element at 32° off zenith may be more effective for estimating the oriented fraction of particles in a volume.