A multivariate correlation analysis of high-frequency bottom backscattering strength measurements with geotechnical parameters

Sound backscattered from the seabed has been measured in a 10 x 10-nmi(2) region of the North Sea, characterized by a variety of bottom types, including mud, sand, and gravel. The backscattering strength measurements are made by a forward-looking sonar, operating at 100 kHz and tilted at an angle of 30 degrees from the horizontal. Fifty bottom-grab samples, representative of the uppermost 20 cm, were taken and analyzed for gravel content, shell content, and grain-size distribution. The backscatter measurements are correlated with the gravel percentage, shell percentage, and median grain size. A strong positive correlation of the measured backscatter strength with shell and gravel percentage is observed. Additionally, a small positive correlation between the backscatter strength and the median grain size of the sand and mud part exists. The derived values for the backscatter strength compare well to those presented in the recent literature. From a least squares curve-fitting analysis, an empirical expression is obtained giving backscatter strength as a function of gravel percentage, shell percentage, and the median grain size of the sand and mud part.