利用局部谐和基小波束的高精度叠前深度域偏移成像方法研究

小波束域利用局部余弦基(local cosine bases)的偏移成像方法具有很高的计算效率和成像质量.然而局部余弦基小波束通常沿垂直方向具有两个对称波瓣.由于缺乏单一定义的方向性,在某些强变速介质中利用局部余弦基的波传播方法会产生一定的误差,同时也使得一些在局部角度域的操作变得非常不便.于是我们提出了利用局部谐和基进行波场外推的方法.局部谐和基(local harmonic base)是由局部余弦基和局部正弦基线性组合而成,具有单一定义的方向性,同时具备快速算法.局部谐和基与Gabor-Daubechies标架类似,都具有单一定义的方向性,但比Gabor-Daubechies标架效率更高.局部谐和基保持了与局部余弦基的偏移成像方法相同的计算效率,但在成像精度上有了显著的提高.通过二维SEG/EAGE模型和BP模型的叠前深度域偏移成像说明了该方法的有效性.

High-accuracy prestack depth migration and imaging using local harmonic basis beamlet

Beamlet migration using local cosine bases (LCB) has good image quality and high computational efficiency. However, local cosine beamlets have two symmetric lobes with respect to the vertical axis. This lack of uniquely defined direction-localization leads to inaccurate modeling of wave propagation in high contrast heterogeneous media, and is inconvenient for many operations in local angle domain. We proposed a new wavefield decomposition scheme using local harmonic bases (LHB), which is implemented by linear combinations of local cosine and local sine bases. Compared to Gabor-Daubechies frame (GDF) beamlet, LHB beamlet is much more efficient because LHB is still orthogonal and has fast algorithm, but it has directional localization which is similar with GDF. On the other hand, beamlet migration using LHB propagators has the same efficiency as LCB propagator but improves the accuracy due to the directional localization built in the propagators. The results of prestack depth migration using the synthetic data of the 2D SEG/EAGE salt model and 2D BP benchmark model demonstrate the good imaging quality and the ability of direction localization.