Real-Time Holographic Water-Drop-Size Measurement System

75699S To fully understand the global warming problem, the properties of the stratus clouds that cover much of the earth must be understood. In particular, new instrument technology is needed to make statistically significant measurements of the size distribution of water drops in these clouds. The regimes of interest include diameters from 3 to 200 microns, with total concentrations on the order of 10 to 100 drops per cubic centimeter. Existing in situ optical instruments, used on research aircraft and on the ground for measuring the drop size distribution of water clouds, are inherently limited in the volume ¿ and thus drop size ¿ they can measure. In the best technology, digital holography, resolution is limited by the large pixels of the imaging CCD cameras. This project will develop a new holographic water drop size measurement system with high-resolution (less than a micron), a highly sensitive (0.1 microjoule exposure level per square centimeter) photothermoplastic recording material for the hologram, and a high-speed and high-resolution CMOS camera for image recording and processing. It will record holograms in real time and increase system field-of-view, meaning that a larger number of droplets can be analyzed. In Phase I, an experimental optical setup was built, holograms of water droplets on photothermoplastic material were successfully recorded, and images from the holograms wre retrieved via a CCD camera. Droplet image sizes were measured directly and also estimated from interference patterns. In Phase II, a fully operational, compact, lightweight prototype system will be developed for real-time continuous hologram recording, development, and retrieval on research aircraft or tethered balloons. Commercial Applications and Other Benefits as described by the awardee: The high-resolution, high-speed, holographic water droplet measuring system should find extensive commercial applications in atmospheric measurement; oil-fired direct-absorbing chillers and microturbines; and biological, medical, university, and research facilities. It also should improve the efficiency of fuel and commercial irrigation systems.