Time reversal echo-to-reverberation enhancement with reverberation nulling constraints based on waveguide invariant

A new echo-to-reverberation enhancement method with reverberation nulling constrains based on waveguide invariant is proposed to solve the problems of direct time reversal processing and the time reversal reverberation nulling method. Firstly, a 2-dimensional signal subspace for the range containing a target potentially is obtained by decomposition of time reversal operator at central frequency. And the bottom focusing weight vector for the target range is obtained by the decomposition of time reversal operator at another range near the target with a frequency-shift, according to the waveguide invariant. Then, combined the optimal array signal processing theory, a constrained optimal excitation weight vector of source receiver array is deduced from the signal subspace and the bottom focusing weight vector, so as to focus sound energy on target while null the sound energy on the seafloor below the target, resulting in echo-to-reverberation enhancement. This method not only remedies the shortages of conventional time reversal processing and the time reversal reverberation nulling, but also obtains an improved performance for echo-to-reverberation enhancement, because of the bottom reverberation nulling constrains at the target range. Numerical simulations in typical shallow water environments illustrate the effectiveness of the proposed method.