USING A DUAL FREQUENCY ECHO SOUNDER FOR THE DETERMINATION OF SUSPENDED SEDIMENT IN THE WATER COLUMN

摘要

The presence of unconsolidated sediment in channels and ports has presented the hydrographic surveyor with a misleading image of the seafloor and created a constant source of conflict between the operator and dredging contractor. In 1985, a revolutionary new concept for defining the nautical bottom, navigable depth, by utilizing the material density was established in the Port of Zeebrugge. At about the same time, investigations by outside contractors put the density of the nautical bottom at about 1.20t/m~3 (Warmer etal 1998). This very soft layer, often layers, of material has not only been difficult to define but has been migratory in nature and in many cases, apparently random in occurrence. In an effort to better locate and delineate the presence of this flocculation, acoustic tests were undertaken over a known fluid mud area utilizing different frequencies. A series of data acquisition lines utilizing different lower frequency transducers were run across the same predetermined paths to ascertain the images and data attainable. The lower frequencies of 12, 24, and 33 kHz were used with and without TVG settings active. The same lines were run with a density measuring device and bottom samples collected top provide a ground-truthing mechanism. The data was processed utilizing acoustic imaging software and was also processed with density imaging software. The various data sets were then compared to see if any correlation to material density, volume, and to nautical depth could be achieved.