Optimal array multimode signal processing in the presence of modal mismatch

Modal mismatch effects on the output SNR of linear and quadratic array processors under the conditions of multimode propagation in a waveguide are presented. The modal mismatch is modelled by the distortion in the sound speed profile, which leads to inaccurate estimation of modal shapes at the array input. Numerical results are presented for the case of 16-element vertical array receiving the multimode signal in the background of spatially-white and modal noise. The channel of signal propagation is simulated for typical shallow-water environments from the Barents Sea and the source frequency of 300 Hz. The scenarios when modal mismatch induces considerable array SNR loss are demonstrated. It is shown that the key factors of mismatch effects are the spatial modal resolution of the signal-carrying modes and intermodal phase shifts.