Paper Summary
To produce a reliable image of the subsurface, we must use a depth-migration scheme that requires a detailed model of the parameter fields for use by migration. Obtaining reliable values of all parameters for the full 3D volume to be imaged is perhaps impractical, so we make various simplifying assumptions. Even with such assumptions, inverting for a wide range of parameters given a limited and inconsistent data set is challenging. Ray-based tomography supplemented with waveform inversion can yield a suitable model. However, we often still need to fall back on various techniques that require manual intervention to incorporate detailed velocity anomalies into the migration model.