The classical Kirchhoff migration method assumes an asymptotic ray theory form of the Green's function. To be consistent with ray theory assumptions, the ray slowness model that produces this function must be a smooth version of the true slowness model. However, the implied wavefield extrapolation through the smooth model introduces diffraction errors. These diffraction errors are predicted via a first order Born approximation that includes a surface and volume integral term. The surface integral represents the wavefield extrapolation through the smooth slowness model and the volume integral is the slowness perturbation contribution to the wavefield propagator.