Matched-field inversion in the time-domain for seabed conductivity

Authors:

  • Berg David

Publish date: 2004-01-01

Report number: FOI-R--1201--SE

Pages: 42

Written in: English

Abstract

In this thesis the feasibility of probing marine sediments by emission of transient pulses with center frequencies in the range 2.5-10 kHz is studied. The main task was to determine the conductivity profile of the different sediment layers below the seafloor. This was accomplished by solving an inverse problem, making use of matched-field techniques. A field trial was conducted in the Stockholm archipelago, where experimental data was gathered. The design of the experiment was to maximize pulse propagation in the sediments. This was accomplished by locating both the receiver and the transmitter close to the sea bottom at a separation distance sufficient to reduce the energy propagating directly through seawater. Ricker pulses of four different center frequencies were transmitted and recorded. The matched-field inversion was carried through using a propagation code and a genetic algorithm. The pulse with frequency 5 kHz was used for the inversion, while the others were used for validation purposes. The inverted profile was used to predict the fields for the measured control set. A good agreement was found supporting the credibility of the modeled conductivity profile.