Digital crossed-beam holography for in situ imaging of atmospheric ice particles

A ground-based outdoor digital-holographic particle imaging system is described, which uses a nanosecond pulsed laser and CMOS cameras in an inline set-up to image atmospheric particles in situ. Sharp images can be digitally reconstructed from the diffraction images. The system uses two crossed beam paths, yielding a total sample volume of roughly 9.9 cm3 where particles with a spatial extent orthogonal to the beam path between 10 µm and several millimetres can be imaged. The set-up allows for two views of objects within an atmospheric cross volume of about 0.3 cm3, defined by the intersecting beams. It is demonstrated how this can be used for an accurate determination of three-dimensional distance relationships within the cross volume, in addition to determining sizes and shapes of moving airborne particles. To this end, results from a field test on the High Altitude Research Station Jungfraujoch in the Alps are shown as examples.

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