A 3D-sensor for the measurement of particle concentration from image sequences

A sensor for the measurement of the concentration and size distribution of small particles is described. The particles are visualized by a light blocking technique and imaged by a CCD camera. The concentration measurement is based on a depth- from-focus approach to determine the positions of the particles in three-dimensional world coordinates. From these coordinate sets of all observed particles both the measuring volume as well as the concentration can be determined. The sensor has been developed for the underwater measurement of size distributions of air bubbles submerged by breaking waves to investigate the influence of air entrainment to air-sea gas exchange.