The coupling-ray-theory tensor Green function for electromagnetic waves or elastic S waves is frequency dependent, and is usually calculated for many frequencies. This frequency dependence represents no problem in calculating the Green function, but may pose a significant challenge in storing the Green function at the nodes of dense grids, typical for applications such as the Born approximation or non-linear source determination. Storing the Green function at the nodes of dense grids for too many frequencies may be impractical or even unrealistic. We have already proposed the approximation of the coupling-ray-theory tensor Green function, in the vicinity of a given prevailing frequency, by two coupling-ray-theory dyadic Green functions described by their coupling-ray-theory travel times and their coupling-ray-theory amplitudes. The above mentioned prevailing-frequency approximation of the coupling ray theory enables us to interpolate the coupling-ray-theory dyadic Green functions within ray cells, and to calculate them at the nodes of dense grids. For the interpolation within ray cells, we need to separate the pairs of prevailing-frequency coupling-ray-theory dyadic Green functions so that both the first Green function and the second Green function are continuous along rays and within ray cells. We describe the current progress in this field and outline the basic algorithms. The proposed method is equally applicable to both electromagnetic waves and elastic S waves. We demonstrate the preliminary numerical results using the coupling-ray-theory travel times of elastic S waves.
Wave propagation, elastic anisotropy, electromagnetic bianisotropy, heterogeneous media, wave coupling, travel time, amplitude, polarization.
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