|dc.description.abstract||The main goal of project RUMBLE has been to enhance our capability to predict active sonar detection ranges in
shallow water. The idea is to measure ‘through-the-sensor’ the seabed characteristics that affects long-range acoustic
propagation in shallow water. The work has included the development of an inversion method for determining bottom
parameters from reverberation received by a Low frequency Active Sonar (LFAS). Two sea trials have also been
performed, in order to provide data for evaluating the performance of the method. The first sea trial took place in a
relatively simple area in Vestfjorden, while for the second sea trial a more difficult area in the Norwegian Trench, west
of Stavanger, was chosen.
The purpose of the present report is to make an assessment of the inversion results; to validate the results against ground
truth, and to estimate the expected improvement of the RUMBLE method over predictions using standard databases.
It was found that reliable measurements could be made of the changes in backscattering strength, but not of sound speed
or reflection loss. Ground truth collected during the trial, grab samples and 38 kHz echosounder, were found to be only
weakly correlated with the LFAS measurements. This shows that near surface properties are of little use as an indicator
of the effect of the seabed on LFAS.||en_GB