Fido-Phi-Pi is a modification of Fido-Phi, designed to develop an in situ 3-dimensional stereo particle image velocimetry system. The data collected with Fido-Phi-Pi is analyzed to better our knowledge of water velocities and turbulent flows in the ocean. Along with understanding the physical structure in the upper 100m of the ocean, Fido-Phi-Pi also assists in profiling detailed view of micro scale phytoplankton distributions. The system has one vertical sheet of laser light (by Melles Griot) serving as the image plane and two Cooke SensiCam QE CCD cameras on either side of the laser sheet. The laser light is used to induce the chlorophyll from the microstructures, which lights as fluorescence. The camera is equipped with special filters to image this fluorescence, capturing images of particles in the laser sheet at a frame rate of 8 Hz. By positioning both camera lenses so that its image plane is parallel to the plane of the laser sheet, it allows us to capture the 2-dimensional in-plane particle displacements. To record the 3rd dimension displacement, both camera lenses will be oriented obliquely (45° during deployment) to the plane of laser sheet. This allows us to capture the movement of particles entering and exiting the plane.