- 1.
__Downward continuation__The first step of migration consists of downward continuation of the wavefield measured at the surface (a.k.a. the data), which is done by the recursive application of the equation

*u*_{0}^{z+1}=*T*_{0}^{z}*u*_{0}^{z}(1) (2) - is the wavefield at depth
*z*, - is the wavefield at the surface (
*z*=0), - is the downward continuation operator at depth
*z*, - is the data, i.e., the wavefield at the surface, and
- is a frequency-dependent scale factor for the data.

- is the wavefield at depth
- 2.
__Imaging__The second step of the migration by downward continuation is imaging. According to the exploding reflector concept, the image is found by selecting the wavefield at time

*t*=0, or equivalently, by summing over the frequencies :(3) - is the image (reflectivity) corresponding to a given
depth level
*z*.

- is the image (reflectivity) corresponding to a given
depth level

6/1/1999