A potential application of the focusing eikonal that we intend to investigate further is reflection tomography. Our preliminary analysis of the linearization errors for domain tomography and domain tomography shows that, when reflectors' movements interfere with velocity perturbations, tomography behaves more linearly than tomography. However, we feel that our analysis is only preliminary. A natural next step is to analyze the back-projection operators, and compare their properties. Further on we should perform full non-linear tomographic tests.
The first time that the first author (BB) heard about ``tracing rays in time'' was from Francis Muir few years ago. He heard about -rays again this summer while visiting Elf's Geophysical Research Center in London.