Ocean Plankton Imaging Using an Electronic Holographic Camera

Abstract—In this paper, we describe an electronic holographic camera that has been developed for in situ underwater studies of the distribution and dynamics of plankton and other marine organisms and particles. Holographic data are stored on an embedded computer in the camera for later data extraction and analysis. We describe the main optical and mechanical specifications and outline the design, development and operation of eHoloCam. We summarise the eHoloCam performance in four in situ deployments in North Sea and Faeroe Channels at water depths ranging from about 10 m to 450 m with research vessel Scotia. eHoloCam is capable of capturing opaque and transparent organisms in the size range from about 50 µm up to a 10 millimetres. A clear advantage of eHoloCam over other imaging and counting techniques is the ability to capture high-resolution images without destroying the organism. This feature is extremely valuable in facilitating new in-situ studies of plankton dynamics. The recorded holographic videos are reconstructed numerically using one of our reconstruction algorithms at various planes through the light path. The overall system resolution for the recorded images is 8 µm and 36 µm at a distance of 100 mm and 470 mm, respectively. We show various images of marine organisms recorded on these 4 cruises, and preliminary data on size distributions of Calanus are also presented and discussed.