Waveguide invariance structure for low frequency monostatic bottom reverberation mitigation in shallow water

The stable range-frequency interference structure （waveguide invariance） of the low frequency monostatic bottom reverberation in shallow water is derived theoretically in this pa- per by using ray-normal mode coherent reverberation model and separable bottom scattering model. And combined the concept of spectral subtraction, a reverberation forecasting and mitigating method based on the waveguide invariance is presented. According to the waveg- uide invariance, the reverberation intensity for a detecting range can be estimated from the reverberation returns scattered from some other range cells nearby the detecting range with frequency shift. Then the reverberation component for the detecting range in the echo can be canceled mostly by using the estimated reverberation intensity, so as to enhance the echo-to- reverberation ratio and improve the detection capability of the active sonar. Simulations in typical horizontal layered shallow water environment show the stability of waveguide invariance structure in the low frequency monostatic bottom reverberation and the efficiency of the reverberation forecasting and mitigating method based on the waveguide invariance.