Prestack migration

If $v_{m}=v({\bf r})$ (when $v({\bf r})$ is true velocity), then for each s the position of reflectors is correct. It is not difficult to show that in this situation the operator $\sum_{s}$ supplies the order of touching $r=\infty$ then, with accordance to equation (140),

q^'_I=q.

If $v_{m}\neq v({\bf r})$ then each reflector's image will be distorted and, in a general case, we shall have r=1, so

$$q\leq q_{I} \leq q+{1\over 2}.$$