Calculating the waveguide invariant by passive sonar lofargram image

An image processing method for the calculation of waveguide invariant (β) with passive sonar lofargram image is presented in this paper. Concise formula for calculating β was then derived by finding the twodimensional Fourier transform ridges of the lofargrams. The algorithm was exercised for a Pekeris waveguide and a simulated shallow water waveguide containing thermoclines with source depth varying from 10m to 90m. It then was applied to a lofargram collected during an experiment at the South China Sea. The result of experimental data matched well to the simulations. The approach in this paper differs from normal mode model algorithm by virtue of its incorporation of image processing methods. It thus avoids the potentially prohibitive computation and accurate estimation of environmental parameters .