f 3D Tomographic Inversion of Travel Times in Irregular Grids

In the travel time inversion, the model space is usually discretized by regular grids. This choice simplifies the ray tracing algorithm, but brings several major drawbacks. Some pixels are not crossed by any ray, and others by linearly dependent rays. These facts originate the null space in the tomographic system, and the consequent non-uniqueness and instabilities in its solutions. Irregular grids allow to reduce the null space dimension, adapting the local resolution to the acquisition geometry and to the desired reliability at the target.