Environment assessment for underwater sensors in the Stockholm archipelago. Part 1 - Inversion of hydroacoustic sub-bottom parameters

This report contains an inversion analysis of data recordings from a field trial in August 2002 in the Stockholm archipelago. The purpose of the experiment was to determine density, velocity and absorption of the seabed. Both the transmitter and the receiver were deployed on the seabottom with a separation distance of 13.2, 23.1 and 45.0 m. The emitted signals were Ricker pulses centered at the frequencies 0.5, 1, 2 and 4 kHz. The inversion is based on travel time analysis of echoes from the sediment interfaces. This analysis gave the following results. The depth to the bedrock is 17.3 m from the seabottom. It is covered by two sediments with the mean velocities 1425 and 1664 m/s and thicknesses 6.6 and 10.7 m. The density and absorption of the top sediment was estimated to 1500 kg/m3 and 0.15 dB/? and in the deep one to 1700 kg/m3 and 0.1 dB/?.