Abstract

For the in situ detection technologies of planktons and fishes, optical cameras traditionally have a small and fixed sampling volume with a strong target-sized dependent ($\text{typically}<1\mathrm{mm}$), and imaging sonar has lower spatial resolution ($\text{typically}>2\mathrm{cm}$) with a problem of species identification. To solve the above problems, this paper proposes an in situ detection method of optical gated sampling for millimeter- to centimeter-scale plankton and fish detection. In this method, the sampling volume can be flexibly adjusted by matching the temporal parameters of gate pulses and illuminator laser pulses to satisfy target observation with different sizes. The gated sampling suppresses the backscattering of water and also filters the environment background so that transparent planktons can be detected by high contrast. Furthermore, the sampling volume is determined by the convolution of gate pulses and laser pulses, and thus the target abundance is derived. Theory and simulation of abundance measurement are established. In experiments, transparent jellyfishes are recorded with a spatial resolution of better than 100 μm. In addition, proof experiments of sampling volume adjustment and abundance measurement are demonstrated.

© 2016 Optical Society of America

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