Imaging in shotgeophone space 
Let the geophones descend a distance into the earth.
The change of the travel time of the observed upcoming wave will be
Simultaneously downward project both the shots and
geophones by an identical vertical amount
.
The traveltime change is the sum
of (9.8) and (9.9), namely,
Threedimensional Fourier transformation converts
upcoming wave data to
.
Expressing equation (9.12) in Fourier space gives

Equation (9.14) is known as the doublesquareroot (DSR) equation in shotgeophone space. It might be more descriptive to call it the surveysinking equation since it pushes geophones and shots downward together. Recalling the section on splitting and full separation we realize that the two squareroot operators are commutative ( commutes with ), so it is completely equivalent to downward continue shots and geophones separately or together. This equation will produce waves for the rays that are found on zerooffset sections but are absent from the explodingreflector model.
Imaging in shotgeophone space 