Holographic data from the prototype airborne digital holographicinstrument HOLODEC (Holographic Detector for Clouds), taken duringtest flights are digitally reconstructed to obtain the size(equivalent diameters in the range 23 to 1000 μm),three-dimensional position, and two-dimensional image of iceparticles and then ice particle size distributions and numberdensities are calculated using an automated algorithm with minimaluser intervention. The holographic method offers the advantages of awell-defined sample volume size that is not dependent on particlesize or airspeed, and offers a unique method of detecting shatteredparticles. The holographic method also allows the volume sample rateto be increased beyond that of the prototype HOLODEC instrument,limited solely by camera technology.HOLODEC size distributions taken in mixed-phase regions of cloudcompare well to size distributions from a PMS FSSP probe alsoonboard the aircraft during the test flights. A conservativealgorithm for detecting shattered particles utilizing theirdepth-position along the optical axis eliminates the obvious iceparticle shattering events from the data set. In this particularcase, the size distributions of non-shattered particles are reducedby approximately a factor of two for particles 15 to 70 μm inequivalent diameter, compared to size distributions of allparticles.
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