An Ultracompact Underwater Pulsed Digital Holographic Camera With Rapid Particle Image Extraction Suite

Abstract

This article presents the design, development, and testing of an ultracompact underwater pulsed digital holographic camera (named weeHoloCam) that has been successfully deployed in the North Sea. With a footprint of 9 cm diameter × 60 cm long and weighing just 3.5 kg, to our knowledge, this is the lightest and most compact system of its kind in the world. It can be easily adapted for mounting on remotely operated underwater vehicles (ROVs) and autonomous underwater vehicles (AUVs). weeHoloCam can record 12 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> of the water column per hologram at 20 Hz and has a capacity to continuously record up to 200 000 holograms, each 5 MB in size. Along with the holographic camera, a field-programmable gate array (FPGA)-accelerated hologram analysis suite has been developed. The 838 megapixel/s reconstruction speed demonstrated is the highest reported speed for a single FPGA implementation to date. This is an extremely important development as rapid processing of recorded holograms is vital for the viability of subsea holographic cameras. weeHoloCam was successfully trialed in the North Sea, recording close to a hundred thousand holograms and extracting particle images within those holograms at a rate of 190 per min. weeHoloCam has the potential to play an important role in several oceanic studies: spatial and temporal monitoring of plankton species; study of plankton dynamics; study of vertical transport of floc; and monitoring microplastic pollution in the ocean, to name but a few.