The reflection trajectory time from the source S to the specular reflection point s r and back via the reflector is calculated from the diffraction trajectory time from the source s to the image point x and back to the reflector r. The rate of coverage of illumination relative to the pair is incremented as a function of the difference between the diffraction and reflection trajectory times : The rates (x, p) of coverage of seismic illumination are estimated with at least one point image x for at least one vector weighting p. For each pair (source s, receiver r) of the seismic picture, the rates I(x, p, s, r) of coverage of illumination relative to the pair is evaluated by determining the time of reflection trajectory t r(x r (p); s, r) between the source S to the specular reflection point s r on the reflection plane containing the image point x and perpendicular to the weighting vector p, and back via the reflector. The diffraction trajectory time t d(x; s, r) is from the source s to the image point x and back to the reflector r. An additional summation stage for each rate relative to a pair determined the total illumination coverage rate I(x, p) = Ss, r (I(x, p, s, r). During the incrementation, the rate is incremented using an incrementation function i(td, t r; s, r) so that I(x, p) = I(x, p) + i(td, t r; s, r) taking into account the difference between the diffraction and reflection trajectory times. The incrementation function is a function of the seismic wavelet s(t) expressed as i(td, t r; s, r) = s(t d(x, s, r) - t r(x r(p); s, r). Alternatively, the incrementation function is a function of the derivative of the seismic wavelet. The migration puts into play a, a priori correction w(x, s, r) for the illumination coverage rate, where the rate relative to a pair is incremented by i(td, t r; s, r).w(x, s, r). The diffraction trajectory time is developed as a second order Taylor series around the image point x. The specular reflection point is defined along the reflector so that the diffraction trajectory time to the specular reflection point is stationary. Independent claims are include for (i) a method of correcting the amplitudes of seismic data recorded during a 3D seismic survey to compensate for the effect of a non uniform illumination from the underground reflectors. This is done by estimating the illumination coverage time as above and using the inverse of this rate as a weighting factor to apply to each amplitude of the data, and (ii) a method of selecting an acquisition geometry for the target of a seismic survey by estimating the illumination coverage rate as above and selecting the acquisition geometry giving the optimum illumination coverage rate as a function of the target.
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