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用有限差分法进行波场全倾角归位的关键在于波场的延拓方向。只要在上行波边界条件的约束下合理地选择波场的延拓方向,就能使来自任何方向的反射波精确归位。沿上行波波前或下行波波前进行波场延拓是确保波场全倾角归位仅能采用的两种延拓方法。差分网格的划分,直接关系到全倾角偏移剖面的质量。采用常规差分网格划分方法,在偏移后的剖面上有可能出现交叉干扰的现象,严重时可使反射波同相轴产生中断与畸变,甚至完全淹没正常反射波。采用加吸收的差分方程和阶梯型差分网格进行偏移,可消除这种交叉干扰。其中阶梯型全倾角偏移既能有效地消除交叉干扰,又能保持大倾角反射波的振幅特性。
Finite difference method for the whole tilt angle wavefield homing is the key to the continuation of the wave field direction. Reflected waves from any direction can be accurately homed as long as the reason for choosing the continuation direction of the wave field under the constraint of the boundary condition of the upgoing wave is reasonable. Wavefront continuation along the upstream or downstream of the upstream wave is the only two continuation methods that can be used to ensure the homing of the full tilt of the wavefield. The division of the differential grid is directly related to the quality of the full tilt offset profile. Conventional differential meshing method may cause crosstalk on the offset section. In severe cases, it may cause interruption and distortion of reflected wave events and may even completely submerge the normal reflected waves. Addition of absorption difference equations and ladder-type differential grid migration can eliminate this cross-interference. Including stepping full tilt offset both effectively eliminate cross-interference, but also to maintain the amplitude of the large dip angle reflection characteristics.