Optical imaging probes
From Glossary of Meteorology
optical imaging probe
(Also called optical array probe.) An optical particle probe that records the size and shape of the shadow of each particle that intercepts and attenuates the illumination by a laser beam.
Of these, shadowing probes differentiate particle shadows from the light of the unobstructed beam with linear arrays of optically activated diodes; for example, the one-dimensional cloud probe normally for sizing 10-μm to either 300- or 600-μm cloud hydrometeors, the two-dimensional cloud probe normally for sizing and imaging 25–800-μm cloud hydrometeors, and the two-dimensional precipitation probe normally for sizing and imaging 200-μm to 6.4-mm precipitation hydrometeors. The electronics record either the maximum one-dimensional width of the shadow or two dimensions and shape of the shadow, to estimate particle size and type (raindrop, crystal growth habit, etc.). Another type, the cloud particle imager, illuminates each particle with a pulsed laser and records size, shape, and detailed structure of each hydrometeor with a high-resolution solid-state digital imaging camera, normally to size 5-μm–2.3-mm hydrometeors.