A preliminary study of the distribution of plankton using hologrammetry

The distribution and dynamics of particles in the aquatic environment play an important role in the modelling of bio-geochemical processes. Previous work on the measurement of such particles, which vary in size from tens of micrometres (individual cells) to several centimetres (aggregates such as 'marine snow'), has mainly used electronic counting or conventional photography coupled with image analysis. Here we report on an initial study of the use of holographic mensuration, otherwise known as hologrammetry, for the enumeration, sizing and spatial distribution determination of plankton. We present results on imaging plankton in water tanks using both in-line and off-axis pulsed-laser holography. In this work, we have recorded in-line holograms in a volume of 2400 cm(3) of water with a resolution of better than 20 mu m and off-axis holograms in a volume of 36000 cm(3) with a resolution of 140 mu m. In both cases, identifiable images of plankton were obtained and precise spatial coordinates determined from the in-line holograms. Copyright (C) 1996 Elsevier Science Ltd.