Calculating the Waveguide Invariant by the 2-D Fourier Transform Ridges of Lofargram Image
利用LOFAR谱图的二维傅里叶变换脊计算波导不变量

A new method is presented in this paper for the calculation of waveguide invariant (β) with passive sonar lofargram image. The distributions of β in two waveguides are studied with normal mode model. Concise formula for calculating β is then derived by finding the 2-D Fourier transforms ridges of the lofargrams. The algorithm is exercised for a Pekeris waveguide and a simulated shallow water waveguide containing thermoclines with source depth varying from 10m to 90m. It then is applied to a lofargram collected during an experiment at the South China Sea. The result of experimental data is well matched to the simulations. The approach differs from normal mode algorithm by virtue of its avoidance of potentially prohibitive computation and accurate estimation of environmental parameters and is more suitable for real-time signal processing.