平面波偏移、分角度成像与AVA道集生成

Plane wave migrating,separated angle imaging and AVA gather generating.

基于波场延拓的叠前深度偏移是实现复杂构造地质体成像的可靠方法,但存在着计算量大、对观测系统适应性差等缺点。平面波偏移是利用波动方程实现精确叠前成像的另一类方法,其基本原理是:通过地表延迟放炮的方式生成平面波震源,利用下行波方程进行波场正向延拓得到下行波场;对地表采集的炮集记录,以组合延迟放炮的方式叠加,得到地表平面波记录,利用上行波方程进行波场反向延拓得到上行波场;二者互相关求和,实现平面波地下波场成像。分析表明:平面波成像技术的精度与单平方根算子的共炮点道集偏移和双平方根算子的共中心点道集偏移相当,但计算速度要快得多,且易于并行计算。二维Mamousi模型数值计算表明,射线参数的范围和间隔是影响平面波成像质量的主要因素;不同角度入射的平面波对最终成像结果的贡献是不同的,据此可以有针对性地选择射线参数进行平面波成像。

Although the wave field based pre-stack depth migration is the most reliable method for complex structure imaging,it has a high computation cost and a poor adaptation to geometry.Plane wave migration is another method using wave equation to realize an accu- rate pre-stack imaging with high efficiency and without migration aperture problem.The basic principles are as follows:plane wave source is generated by surface-delayed shooting,and the down-go- ing wave field is obtained by forward continuation on down-going wave equation;plane wave record is superimposed and composited from shot gathers at surface by array-delayed shooting,and the up- going wave field is obtained by up-going wave equation.The two cross correlations sum up to realize plane wave imaging at subsur- face.Numerical calculation indicates that the plane wave imaging is a rapid and efficient method with low computation cost.Mean- while,it is easy for parallel computation,in similarity with single square-root operator imaging for common shot gathers and double square-root operator imaging for common middle point gathers. The 2D Marmousi model calculation shows that the range and in- terval of ray parameters are the main affecting factors for imaging quality.The plane wave with different incident angles has different contribution to the final imaging result,and based on it,the ray parameters can be correctly selected for plane wave imaging.