A camera and image-analysis system for <i>in situ</i> observation of flocs in natural waters

An in situ suspension camera in combination with an image-analysis system was developed at NIOZ to measure the in situ particle size of suspended matter. It differs from other methods in that in situ particle size is measured from ~ 4 µm upwards in a relatively simple and direct way. It can be used in any waters down to ~ 4000 m depth (with some adjustments to 7000 m) and in water with a suspended matter concentration up to 200 mg·dm -3. In very clear ocean water the system becomes inconvenjent because of the large number of photographs that have to be taken to obtain a reliable size distribution. This paper describes the camera and the image-analysis system and gives some results of measurements in the Scheldt river and estuary in April 1989. These measurements show a continuous size distribution by volume between 3.6 µm and 644 µm and a good agreement of the data obtained with the 1:1 and 1:10 cameras