The effect of changing scatterer positions on acoustic time-reversal refocusing in a 2D urban environment at low frequencies

Abstract

In a previous work, we considered time-reversal refocusing for localizing a sound source in a highly reverberant urban environment with non-line-of-sight (NLOS) receivers. The approach involved a virtual (computer-based) time-reversal propagation calculation using a priori knowledge of the receiver and scatterer positions. Among the errors that affect the quality of refocusing is the imperfect accuracy of the assumed scatterer locations. Some practical analogues of changing scatterer positions are (a) the building coordinate errors (or mistakes) and (b) the random movement of vehicles on the street of an urban setting. We address these issues by conducting a time-reversal analysis of a set of numerically generated synthetic acoustic pressure recordings after intentionally introducing errors by altering the position of the scatterers. The numerical experiment results indicate that, for a realistically complicated urban setting, coordinate errors in the position of only a few scatterers have little detrimental effect. The effect of coordinate errors in one or a few scatterers is suppressed by the constraints imposed by correct propagation features (both kinematic and dynamic) generated by multiple reflections and diffractions from other precisely located scatterers. The dependence of source localization accuracy on the relative error in scatterer coordinates, the relative number of scatterers with coordinate errors and the number of receivers is quantitatively assessed in this paper. In general, time-reversal refocusing with a large number of receivers can compensate for more severe errors. Even for only three non-line-of-sight receivers, building location errors in the order of 3 m still give good results. Adding small scatterers (like vehicles) close to a receiver is more critical than adding scatterers relatively far from the receivers.

Multiple-array passive acoustic source localization in urban environments

“…While many studies have been done on the consequences of imperfect models 23 and it is almost always assured that model uncertainty will degrade beamformer performance, the extent of the degradation is both model specific and highly dependent on the array-source geometry as shown previously. To quantify the impact of mismatch on performance, it is necessary to search a large domain.…”

“…Some of the effects of model uncertainty have been studied in the context of time reversal refocusing. Liu et al 23 found that localization was generally tolerant of minor changes in scatterer position, although the addition of an obstacle close to a receiver caused substantial degradations. Yon et al 15 reported similar robustness to perturbations such as moving persons within a room.…”

Localizing Perturbed Objects in a Room with Reflective Boundaries Using Dispersed Acoustic Measurements

“…It has previously been shown that time-reversal is a self-averaging process and can focus a signal back to its source in a multiple scattering environment and that source localization is successful when a broadband impulse is transmitted rather than a single frequency signal [1]. Time-reversal was also shown to be effective in locating a perturbation in a 2D urban environment [2]. This is important because an urban environment presents the challenge of large objects obscuring acoustic receivers and sources as there is no direct line-of-sight path from an acoustic source to any receivers.…”

A Scenario Study for Improving Cost-Effectiveness in Acoustic Time-Reversal Source Relocation in an Urban Environment

“…1. 12,14,15 This flat area has 15 closely spaced concrete buildings arranged in a 200 m by 140 m area. The impulsive sound source was placed at the center of the main street Locations of the buildings, the acoustic source (the asterisk, the location is referred as S1 hereinafter), and receivers for the numerical experiments.…”