A New 1D2D Optical Array Particle Imaging Probe for Airborne and Ground Simulation Cloud Measurements

A new optical array imaging probe, called the 1D2D probe, has been developed by Science Engineering Associates, with features added to improve the real-time and post-analysis measurements of particle spectra, particularly in the Supercooled Large Droplet size range. The probe uses optical fibers and avalanche photodiodes to achieve a very high frequency response, and a Field-Programmable Gate Array that performs real-time particle rejection and processing of accepted particles with negligible inter-particle dead time. The probe records monochromatic two-dimensional images, while also recording the number of individual particle pixels at a second grey scale level. The probe implements flexible features to filter recording of highly out of focus particles to improve the accuracy of particle size determination, or to reject small particles to improve the statistics of measurements of larger particles. A real-time one-dimensional particle spectrum is computed similarly to the original generation of 1D optical array probes, which will be refined using the advanced features as practical experience is achieved. A technique is described that shows promise in providing such a real-time spectrum with sufficient liquid spectrum MVD accuracy for icing wind tunnel calibration. The probe is housed in a cylindrical canister compatible with existing optical array probes, but with substantial additional de-icing. It has been tested in the laboratory, and at two wind tunnels, and tests include some comparisons to another commercially available probe. Probe design and performance, and preliminary results and comparisons are described.