A velocimetry apparatus and method for the collection of target-specific images of fluid motions are disclosed. The apparatus includes a camera and a light source. The camera collects and provides images of the fluid showing instantaneous positions of particles in the fluid. The light source provides a light sheet (two-dimensional) or volume (three-dimensional) to illuminate the particles. The camera and the light source are powered by portable energy sources and measure instantaenous velocity of the fluid in a field of view. Shape and distance between first camera, the light source and the portable energy sources are so configured that the apparatus is a self-contained apparatus portable by a diver during operation thereof.