What is the difference between time and depth when it comes to diffraction and sensitivity to velocity
?
Well you'd never normally depth convert a stacked (normal ray) section, so it doesn't really come up. Or rather, I'd be asking what your goal is when you do it(!) Mostly depth conversion is for the picked horizons rather than the seismic data when it comes to deeper seismic. The problem is that in depth, the layer depth depends on the interpretation you make - change the interpretation of a key velocity boundary and the depth changes...
"As a stacking operator for diffractions, Double Square Root operator provides an exact traveltime for a point diffractor
in a homogenous medium"
Um, its a nice model but doesn't work for real rocks??
So joking aside (real rocks tend not to be very homogeneous - they have velocity gradients from compaction and structure) its saying that the double square root operator is not too bad of an approximation if the velocities are not varying too much, and can be used to collapse a diffraction back to a point source.