Acoustical classification of the bottom sediments in the southern Baltic Sea

The basic relationship is described between the parameters of backscattered acoustic signal and the seabed type in the Polish Economic Zone of the Baltic Sea. The properties of the bottom backscattered signal were investigated using a single frequency narrow beam echosounder working at a frequency of 30 kHz. For approximately 15,000 averaged echo pulses acquired in the survey area, calculations of integral backscattering strength, spectral width and Hausdorf fractal dimension were performed and the correlation of the results with bottom characteristic features were evaluated. The chosen set of echo parameters is a good descriptor of the sea bottom sediments and may be used for classification procedures. Having applied cluster analysis to the data sets of averaged echo envelopes, it was possible to classify them into four groups. The groups corresponding to the four cluster centers were assigned to a given type of sediment. The surficial sediment types most often occurring in the southern Baltic are: muddy deposits (deeper part of the study area), clay, fine and medium grained sand, coarse sand or gravel.