Performance Study of Two-Beam Interferometric Velocimetry for Seawater Particles Measurement

This study presents a two-beam interferometric velocimeter based on the measurement of scattered light from particles in the air and in the natural seawater. A 638 nm narrow-linewidth diode laser was deployed as the light source. By optimal design of spatial components in the light receiver, the receiving efficiency was enhanced significantly that enabled the measurement of the weaker scattering signal from the particles in seawater. Such a velocimetry was calibrated by both the rotating disk and the towing sliding rail on the water tank. It has demonstrated experimentally that the velocimetry has a range of 0.00565–31.29
$\text{m}\cdot \text{s}^{-{1}}$
in the air, and a range of 0.01–2.50
$\text{m}\cdot \text{s}^{-{1}}$
in the water with particles size as small as
$50 \mu \text{m}$
in diameter. The applicability of the system in natural seawater was verified in spring seawater of Aoshan Bay, Qingdao, Shandong, China, with a turbidity range of 0.5–51.8 NTU, particle size range of 66.9–
$352 \mu \text{m}$
, and minimum velocity of 2 mm
$\cdot \text{s}^{-{1}}$
.