A New Instrument for Reliable Airborne Measurements of Cloud Liquid Water Content and Drop Size Distribution

75342-The Department of Energy¿s Atmospheric Radiation Measurement program assesses the radiative impact of clouds by using remote measurements from the earth¿s surface and from space. However, a cloud¿s radiative properties are strongly influenced by its liquid water content and drop size distribution. Correlation of remote and in situ measurements has been hindered by uncertainties in the airborne sensors that measure liquid water content and drop size distribution, especially in clouds with a broad drop size distribution. This project will design and fabricate an airborne cloud drop spectrometer that will make reliable measurements of the liquid water content and drop size distribution from 3 to 200 ?m in stratus clouds. The work will build on previous R&D in which a prototype cloud drop spectrometer reliably measured relatively high (0.5 to 3 g m-3) liquid water content and broad drop size distribution in cumulus clouds. However, instrument stability limitations prevented the instrument from measuring the relatively low (0.01 to 0.5 g m-3) liquid water content typically found in stratus clouds. Phase I will identify a very stable laser source that produces a well-collimated, stable output beam. The new collimated light source will be integrated with a digital camera into a breadboard optical system, and its electro-optical stability and accuracy will be evaluated on a vibration table in an environmental chamber. Commercial Applications and Other Benefits as described by the awardee: The cloud drop spectrometer will be used to validate remote retrievals of stratiform cloud drop size distribution and liquid water content, a critical component in the DOE¿s Atmospheric Radiation Measurement program to better understand radiative cloud processes and global climate change. A commercial cloud drop spectrometer also should find applications on research aircraft, as a ground-based instrument to measure fogs and cloud conditions on mountaintops, in icing wind tunnels, and to analyze drop size distribution in industrial sprays (e.g., paint, fuel, and agricultural sprays).