The method of identification of cloud phase by using micropulse lidar

In the process of global climate change and weather forecast, the cloud is an important parameter. The complex change mechanics among different phases of cloud and the dramatical changes in its time and space dimension results that cloud is the variance that's the most difficult to describe among the metrology elements. In the future of cloud and radiation parameterization scheme, the introduction of detailed micro-physical processes is an essential development, therefore, it's very important to research the cloud parameters. This paper uses Micropulse Lidar (MPL) to discriminate cloud ice/water phase. MPL systems provide continuous, autonomous observation of nearly all significant atmospheric clouds and aerosols. Being compact in structure and with eye-safe transmitted radiation, the systems proved reliable in a number of experiments both at home and abroad. MPL primarily use depolarization ratio to classify cloud phase as ice or water, the transmitted lidar beam is nearly 100% linearly polarized. Depolarization of the return signal from the molecular atmosphere is about 0.35% due to narrow optical bandwidth of the receiver which blocks most of the highly polarized Stokes and anti-Stokes lines. It is well known that backscattering from ice crystals results in appreciable signal in a polarization plane perpendicular to the plane of the transmitted lidar beam. Depolarization from ice crystals depends on crystals shape and aspect ratio and is typically in the range of 30%-50%. In contrast, backscattering from spherical water droplets preserves the polarization of the incident light.