Advances in polarization diversity lidar for cloud remote sensing

As soon as high-energy pulsed lasers became available in the mid-1960s, atmospheric scientists began assessing the information contents of various light detection and ranging (lidar) techniques in the field and laboratory. A particularly promising approach, which has recently gained increased stature as a result of growing interests in previously overlooked cloud types important to climate research (e.g. high-altitude cirrus), involves the polarization analysis of the backscattered laser return. Polarization diversity lidars collect data simultaneously in two or more channels to remotely determine the thermodynamic cloud phase, structure, and boundaries, and infer a variety of other climatically important cloud microphysical properties. As illustrated by the description of the mobile University of Utah Polarization Diversity Lidar system, commercially available dual-wavelength transmitters and improved electronic technologies to process high-resolution multichannel lidar signals represent significant advantages over earlier devices used in cloud studies. Polarization diversity can be added rather economically to more specialized lidars employing spectroscopic techniques, for other forms of atmospheric probing, such as Raman, differential absorption, and high spectral resolution lidars, in order to enhance instrument accuracy and versatility for cloud an aerosol research. Future engineering challenges remain in the “hardening” of compact lidar systems for extraterrestrial deployment, the achievement of unattended eye-safe operations, and in the improved integration of multiple remote sensor data streams and supporting in situ measurements to more fully characterize cloud systems and their effects on the Earth´s radiation balance