The light source for the PIV system is a dual-head, pulsed, 350 mJ/pulse dye laser, which generates pairs of 2 microseconds pulses at 594 nm wavelength. The laser is located on the surface vessel and the light is transmitted through two 400 micrometer diameter optical fibers to submerged probes, each containing the light-sheet forming optics, which illuminate the two sample areas. Images are acquired using two 2048 x 2048, 12 bits/pixel CCD cameras (Silicon Mountain Design 4M4, now Dalsa), each capable of sampling at up to 4 frames/sec, producing a maximum data rate of 32 MB/sec per camera. The CCD chip of each camera has 14 x 14 micrometer pixels with 100% fill factor, making it quite sensitive and robust for oceanic application. Each camera and associated light sheet can be aligned independently, in the same or different planes, near each other or apart. The data is recorded on two 240GB, ship-board data acquisition systems (one for each camera), each comprising six 40GB IDE disks.
The submersible components of the PIV system are attached to the profiling platform (see figures below) via rigid framework of x-rail beams, which in turn are attached to a hydraulically operated turntable. Profiling platform consists of a telescopic hydraulic cylinder with five stages mounted vertically on a tripod base. The system can be rotated to align the sample areas with the mean flow direction, and extend vertically to sample the flow at different elevations. When fully retracted the entire system elevation is 2.5 meters, and when fully extended it is 12.3 meters high. The flow direction is determined by monitoring the orientation of a vane mounted on the platform using a submersible video camera. Two hydraulic hoses (high and low pressure lines) link the platform to a ship-board hydraulic power supply which uses environmentally friendly food-grade hydraulic oil (ZFX AW32, zinc free). A remotely controlled manifold at the top of the cylinder is used to switch operation between the hydraulic turntable motor and the cylinder.
System fully rigged and ready for deployment. The present configuration includes: distance between cameras and the light sheet of 120 cm (in air), cameras have sample areas of 35 x 35 cm^2 each, and are separated horizontally by 31 cm.
