The design of a miniaturized in-situ shadow photographic imaging system for plankton research

Understanding the distribution of plankton in the ocean ecosystem is critical as the plankton of a broad range of species constitute the primary staple of marine species. To monitor the dynamic variation in space and time of plankton in a long term, various techniques have been used to characterize the plankton distribution in the ocean. In this article, based on shadow photographic imaging technology, a compact and miniaturized in-situ system is designed to provide high-resolution spatial and temporal data on plankton abundance, biomass, and size. A 610 nm LED is used as the illumination source, which attenuates fast, and most marine organisms, including motile plankton, are least sensitive to red light, after the lighting, the plano-convex lens creates a collimated light field in a water body, to generate the shadow image of the sampling target in the water body on the CCD on the other side. And the diameter of the proposed system is only 70 mm, the length is 620 mm. In terms of the optical performance, the resolution, field of view, and depth of field are 50 um, 17.67x14.88 mm2, and 100 mm respectively, theoretically, about 26 mL of seawater parcel can be investigated with each exposure. The system has been deployed in the nearshore area of the South China Sea, deep learning technology is used to process the data acquired by the system.