Improved effective sound speed estimation method for fast range estimation of active sonar in bottom bounce area

In deep ocean environments,the bottom bounce mode associated with the low-frequency active sonar is often used to detect the underwater target located in the first shadow zone.However,range estimation error occurs due to the varying sound speed,which produces a bending acoustic ray path from the sonar to the target.To reduce the active ranging error,a method that uses the effective sound speed can be used.However,this method faces a heavy computation burden due to the calculation of the time delay-effective sound speed pairs at each grid position in the bottom bounce area.To reduce this computation burden,an improved effective sound speed estimation method based on the interference structure of the sound field is proposed.The sound field fluctuation in the bottom bounce area is due to the energy fluctuation of the sound rays having different grazing angles.A quantitative relationship between the detectable areas and the sound rays with high energies is established based on sound ray interference theory.The time delay-effective sound speed pairs in the boundary location of the detectable areas are calculated according to this relationship.Hence,the time delay-effective sound speed pairs at all the grid positions can be obtained by linear fitting.Simulation results show that the improved method can obtain a similar range estimation error as the conventional effective sound speed estimation method but has a much lower computation burden,which is useful for real-time applications.