Tutorial: Time conversion of depth migrated data

Abstract

Many data processing and interpretation procedures are performed on time domain data. If such procedures are to be applied after a depth imaging project has been conducted, it is necessary to convert the data to the time domain from the depth domain. Although there will be a velocity-depth model available that was used for the depth migration, in this tutorial note I show why it is inappropriate to use the depth migration velocity model for depth-to-time conversion if additional processing is to be performed on the prestack data in the time domain. The situation is less clear-cut if the objective is to compare the time-converted depth image to checkshot or interval times. It should be noted that time conversion of depth migrated data is subtly different from depth conversion of time migrated data. For time migration, the velocity field is inherently smooth: this is not the case for depth migrated data, and as I show in this tutorial, this lack of smoothness is the issue.