Turbulence Distributions and Flow Structure in the Coastal Ocean from PIV Data

The present version of the submersible system comprises two 2Kx2K pixels, 12bits/pixel digital cameras operating simultaneously, each with a sample area of up to 0.5x0.5m. In the present configuration we record two exposures within each frame of the digital cameras. A hardware based 'image shifter' creates a known fixed offset between exposures on the CCD array to remove directional ambiguity. The cameras can capture up to 4 frames/s, requiring a total image acquisition rate of 64Mb/s. The data is stored using ship board hard disk arrays. When the two sample areas are aligned horizontally in the same plane, and spaced 1m apart, they enable us to resolve turbulent scales ranging from about 8mm (the vector spacing) to 1.5m. The light source of the PIV system is a pair of flashlamp pumped dye lasers located at the surface, whose beams are transferred to each of the sample areas using two independent optical fibres (see Figure 1). Submerged probes are used for expanding the beams into light