A CAMERA AND IMAGE-ANALYSIS SYSTEM FOR INSITU 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 approximately 4-mu-m upwards in a relatively simple and direct way. It can be used in any waters down to approximately 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 inconvenient 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-mu-m and 644-mu-m and a good agreement of the data obtained with the 1:1 and 1:10 cameras.