We presented a new surface boundary condition for downward continuation using the one-way wave equation which improves the amplitude distribution along the wavefronts. This new surface boundary condition is the Green function of the Helmholtz equation for a constant velocity medium at z=0. The results, in both the constant velocity and VOZ models, show that the new surface boundary condition produces wavefront amplitudes that match better the theoretical curve than the traditional and Zhang's.
Both Zhang's surface boundary condition and the Green function surface boundary condition behave similarly in the Marmousi velocity model, resulting in better imaging of steep dips than those obtained with the traditional surface boundary condition.
More research needs to be done to study the AVA amplitude responses and phase differences due to the use of different surface boundary conditions.