We present a method for computing the angle-domain illumination, or more generally, the angle-domain Hessian.
The method takes advantage of the relation among scattering angles, dip angles, CMP wavenumbers and subsurface-offset wavenumbers,
and uses a simple Fourier-domain mapping to transform from subsurface offset domain into angle domain.
Our method can decompose the illumination or Hessian into either scattering-angle domain suitable for point scatterers,
or dip-dependent scattering-angle domain suitable for planar reflectors. A straight forward implementation of our method, however,
can be very expensive. We show how the cost can be drastically reduced by using the phase-encoding technique.
Numerical examples demonstrate that our method can produce accurate illumination estimation for both point scatterers and
planar reflectors, and therefore, it is useful for application related to AVA analysis or robust migration velocity residual parameter estimation.