Performance Testing of the Ground-Based and Snowflake Disdrometer Systems.
Final rept. 10 Apr 67-13 Jan 71,
TECHNICAL OPERATIONS INC BURLINGTON MASS
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Instrumentation to record and size naturally occurring aerosol droplets in the 5 to 100 micron diameter size range has been constructed and tested. Two systems were constructed, the ground-based disdrometer and the snowflake disdrometer. In the ground-based disdrometer, an optical Fourier transform of the sample volume is taken. The Fourier transform is sampled electronically and, through a mathematical inversion performed in a computer, the number and size of the fog droplets are computed directly. This type of system is capable of recording fog distributions without the necessity of manually counting and sizing the particles. In the snowflake disdrometer, a pulsed ruby laser illuminates the sample volume, and the laser beam is interfered with a reference beam to form an off-axis Fraunhofer hologram. The short time pulse of the laser stops the motion of the particles and provides an instantaneous sampling periodically over the history of the particles. When reconstructed, the hologram provides results comparable to high resolution photography with vastly improved depths of fields up to 20 inches. Author