MEASUREMENT OF ACOUSTIC ATTENUATION IN MARINE-SEDIMENTS BY IMPEDANCE TUBE

A new in situ method of measuring the attenuation constant of marine sediments is developed and described. This technique relies on the use of a submerged impedance tube that is pushed into the surface of the seabed. The acoustic impedance of the section of the tube filled with sediment is then measured in the frequency range 1-3.5 kHz using conventional impedance tube techniques and values of attenuation constant and sound speed determined. The system has been deployed on several sand sediments in shallow water. The attenuation constant of these sediments was found to be 0.01 +/- 0.002 Np/m, a value in the range expected for sand sediment at these frequencies. The sound speed determined by the method is of low precision but in agreement with the sound speed measured by the conventional pulse transit method. The technique offers the opportunity to make measurements of acoustic attenuation in an important frequency range between conventional high-frequency (50 kHz) techniques and remote low-frequency (below 500 Hz) methods.