Inversion for the sea bottom acoustic parameters by using the group time delays and amplitude of normal mode

The group time delays and amplitudes of the normal mode are derived using the normal mode filter. The sea bottom sound speed, density and attenuation are inversely deduced by matching the group time delays and the amplitude of the normal mode. A genetic algorithm (GA) is used for optimization search in the parameter space. The inverted attenuation has the nonlinear frequency relationship α=0.29f^1.9dB/m(the unit of frequency is kHz) in the frequency range 200 - 500 Hz. The theoretical transmission loss calculated using the deduced parameters matches the experiment data very well.