A SCENARIO STUDY FOR IMPROVING COST-EFFECTIVENESS IN ACOUSTIC TIME-REVERSAL SOURCE RELOCATION IN AN URBAN ENVIRONMENT

Abstract

Through finite difference time domain (FDTD) numerical simulation, we have studied the possible observation settings to improve the cost effectiveness in time-reversal (TR) source relocation in a two-dimensional (2D) urban setting under a number of typical scenarios. All scenario studies were based on the FDTD computation of the acoustic wave field resulted from an impulse source, propagated through an artificial village composed of 15 buildings and a set of sources and receivers, a typical urban setting has been extensively analyzed in previous studies. The FDTD numerical modeling code can be executed on an off-the-shelf graphic processor unit (GPU) that increases the speed of the time-reversal calculations by a factor of 200. With this approach the computational results lead to some significant conclusions. In general, using only one non-line-of-sight (NLOS) single receiver is not enough to do a quality work to re-locate the source via time-reversal. This is particularly true when there are more than one path between the source and this receiver with similar wave energy travel time. However, when the single sensor is located in an acoustic channel, reverberation inside the waveguide may increase the effective aperture of the single receiver enough to give a good location. It is equivalent to say that the waveguide and the single receiver form a "virtual array". It appears that a sensor array with a minimum number of three receivers might be the most cost-effective way to carry out TR source relocation in an urban environment. The most optimal geometry of a sensor array with a minimum number of three receivers could be an equal side-length triangle. Simple analysis showed that by this setup it is possible to catch sound sources from almost all possible azimuths. Effective source relocation essentially depends on the geometry, relativity to the scatters, etc. of the sensing array. Generally, adding another single sensor relatively far away from the main array will not improve the results. It is practically useful and achievable to have a sensor array mounted on the outside of a single building, and in these cases successful source relocations were obtained. As stated by the fundamental TR theory, increasing the number of scatters, here, increasing the number of buildings will definitely be helpful to increase the effectiveness of TR source relocation.