Dual-side snapshot light field imaging for accurate 3D volumetry of opaque and drifting underwater particles

Accurate <i>in-situ</i> volume measurement of small (1 mm-10 cm) drifting underwater particles is critical for marine ecology and pollutant monitoring, yet it demands snapshot 3D imaging to avoid motion artifacts. Existing imaging techniques-including digital holography and conventional light field imaging-face a fundamental limitation in recovering the complete surface geometry of opaque and semi-transparent particles due to optical occlusion and limited perspective sampling. We overcome this challenge with a face-to-face dual light field camera (F2F-DLFC) system, which simultaneously captures both sides of a target under incoherent dark-field illumination. This dual-side snapshot strategy enables full 3D reconstruction of opaque particles, with experimental results showing volume errors below 6% for targets such as live fish and irregular pellets. While semi-transparent objects still present reconstruction challenges, this work establishes a foundational methodology for <i>in-situ</i> volumetric instrument development, providing a viable approach for accurate volumetry of a wide range of underwater particles.