Unresolved velocity anomalies in the near-surface degrade deeper imaging. As a consequence, great care needs to be taken to ensure that all significant near-surface effects have been dealt with before attempting to build the deeper parts of a velocity depth model. In order to incorporate velocity anomalies into the model, a range of options can be used, depending on whether just the geo body geometry alone is discernible, or whether its velocity distribution as well is known. 

 Here, I’ll describe current industrial practice for building complex near-surface models, which is based on a range of approximate techniques, as well as the more complete solution offered by the emerging technology of waveform inversion. It will be shown that, although usually painstaking, a suitable near-surface velocity model can often be obtained..