Validation of the new depolarization channel at 532 nm of the UPC multi-wavelength lidar

Abstract

The Remote Sensing Laboratory (RSLab) in Universitat Politècnica de Catalunya (UPC) operates a 7channel lidar to detect atmospheric particles. The multi-wavelength characteristic of the system allows for the use of advanced techniques and methods to retrieve, not only the aerosol optical properties, but also information on their size, shape, etc. The purpose of this project is to assess the proper functioning of the new depolarization channel at 532 nm. This channel, installed in 2016, measures the quantity of light backscattered with a polarization direction perpendicular to the emitted one. We first use the optical software Zemax to make the raytracing of the actual optical setup in order to verify the correct arrangement of all the components within the optical channel. Then, a detailed analysis of the two received powers of interest (total and perpendicular) is described. The procedure and the stability of the calibration over the last 18 months is presented. Finally, the retrieval of the volume and particle depolarization ratios and their associated error bars is described. The validation of these products (volume and particle depolarization ratios) is made by comparison with the same quantity retrieved from a co-located lidar. At the very end, retrievals under different atmospheric scenes (low and high mineral dust loads, clouds) are presented as illustration.