A system for counting the number and size distribution of particles in sea water ranging from 250 microns to several millimetres in size. LAPS consists of a video camera synchronised with a strobe light which flashes at predetermined intervals as the instrument is lowered through the water column. The light is focused so it illuminates only a narrow slab of water where the video camera records images of the large particles in the water. The video images are analysed using software which counts the number of particles and determines their maximum and minimum dimensions if they are not circular, and this data is used to estimate a volume and mass of the imaged particles. LAPS is an integral part of the Particle and Optics Profiling System (POPS).