Retrieval of the polarization gain ratio for polarization lidar using a hybrid data method

In cirrus conditions, the polarization gain ratio of a polarization lidar can be accurately determined using the hybrid data method, which relies on two sets of detection data: one obtained under a known polarization gain ratio and the other under an unknown ratio. From the extensive measurements acquired between January 2005 and January 2008 using a polarization-Mie scattering lidar equipped with a polarization gain ratio measurement unit, 10 datasets were selected based on their suitability for retrieving the polarization gain ratio via the hybrid data method. In addition, the corresponding gain ratios for these datasets were measured by the lidar's built-in gain ratio measurement unit. The gain ratios derived from the hybrid method were subsequently compared with those obtained using a polarization calibration device; the maximum discrepancy between the two methods was found to be 0.01. It is evident that, within a certain period following a single polarization gain ratio calibration, the hybrid data method can yield an accurate polarization gain ratio for the corresponding datasets. However, the polarization gain ratio obtained through this method is susceptible to the influence of aerosol changes around the cirrus layer.