Three‐dimensional spatial coordinates of individual plankton determined using underwater hologrammetry

We report the use of a nondestructive metrological technique, hologrammetry, that affords greater scope and higher accuracy for the enumeration, sizing, and spatial distribution of particles. Results are presented on imaging of three living planktonic protists suspended in water using in‐line pulsed‐laser holography. We demonstrate that a volume of 2,400 ml of water, at 750 mm depth, can be analysed with a resolution everywhere better than 20 μm. High quality images and accurate spatial coordinates of living plankton in subvolumes have been obtained.