Real-Time Holographic Water-Drop-Size Measurement System

75699-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 water drop size measurement system with high resolution (less than a micron), high sensitivity (ten million square centimeters per joule), and the use of photothermoplastic recording materials both for the hologram and for image recording. It will allow the holograms to be recorded in real time and will increase system field-of-view, and consequently the number of droplets that can be analyzed. In Phase I, an experimental optical setup will be developed to record water droplet holograms on photothermoplastic material, and the image retrieved from the hologram will be recorded on another high-resolution photothermoplastic material. Droplet image size will be measured directly or estimated from the interference pattern in a defocused image. 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 technology; oil-fired direct-absorbing chillers and microturbines; and in biological, medical, university, and research facilities. It also should improve the efficiency of fuel and commercial irrigation systems.