Holographic Aerosol Particle Imager (HAPI). (a) Model showing the major components of the instrument, which include the electronics, sensing, and optics compartments. Cutaways from the outer enclosure show the approximate configuration of the elements as labelled (see “Methods”). (b) Photograph of the actual instrument with portions of the outer protective casing removed. Leaders identify the location of the components relative to the diagram in (a). (c) A photograph of the HAPI instrument in-flight during a field trial near a pollinating tree. The black, disk-shaped objects visible on the instrument are sunshades that help limit the intensity of ambient sunlight reaching the sensing volume.