Development and laboratory assessment of a subsea particle image velocimetry system for bubble and turbulence measurements in marine seeps

We present the development and laboratory evaluation of RPiPIV, an underwater particle image velocimetry (PIV) system controlled by a Raspberry Pi. Designed specifically to measure bubble characteristics and bubble-induced flow in natural hydrocarbon seeps, RPiPIV comprises three primary pressure enclosures, housing a consumer-grade laser for particle illumination, a Gig-E camera for image capture, a Raspberry Pi for system control, and essential supporting electronics for voltage conversion, battery management, and remote connection. Operating on 24–36 V DC power, the RPiPIV system can be deployed tethered onto a remotely operated vehicle or self-contained for extended duration measurements. Comparing the RPiPIV and a laboratory high-speed camera system, we conducted assessments of bubble imaging in a bubble stream and PIV measurements in a water jet, bubble-chain flow, and single-orifice bubble plume. Laboratory assessments revealed that bubble diameter estimates differed by approximately 5%. In PIV measurements, mean axial velocities exhibited differences of approximately 5%, while turbulent normal and shear stresses showed variances within 10–30%. Dissipation rates of turbulence kinetic energy differed by approximately 60%. These findings underscore the system's potential for reliably quantifying complex multiphase flow characteristics in deep-sea environments.