The Smile Equation for Velocity Estimation
, by Bert Jacobs
Downward Continuation of both shots and geophones using the double square root equation is called SG migration. A proper SG migration leaves no energy at non-zero offsets. If the wrong velocity structure is used them smiles are generated. From a measurements of the curvature of these smiles (and frowns) it is possible to construct a correction to the velocity model used in the migration.
STANFORD