Imaging changes in scattering media from Time Reversal of the Coda wave Difference (TRECOD)

Abstract

We propose a new method for monitoring temporal changes in a complex scattering environment. It is referred to as Time Reversal of the Coda wave Difference (TRECOD). The impulse responses of the probed medium are recorded between all the emitter/receiver pairs of a transceiver array. A Fourier transform of these responses then produces the so-called backscattering transfer matrix at each frequency of the transceiver bandwidth. The matrix acquisition is repeated and the image of the temporal changes occurring between two matrix acquisitions is formed by propagating numerically the significant singular vectors of the matrix difference. Small-scale experiments with ultrasound are used to validate the method and demonstrate its interest for the monitoring of a fluid injection in a porous medium behind a strongly scattering obstacle.

Acknowledgements

This work is part of the project EMSAP co ₂ funded by the French research national agency ANR. We thank our colleagues Matthieu Davy and Frank Philippe David for useful discussions and advice.

Notes

Notes

1. French acronym for “Décompostion de l'Opérateur de Retournement Temporel”.

2. In our experimental conditions, the lateral resolution given by the Rayleigh criterion is ℛ = λ F/ d∼ 2.3 mm, where F is the distance between the transducer array and targets, and d is the array aperture.