## 4 Results and Analysis
### Field Measurement Results and Analysis
#### 4.2.4 Migration Parameter Selection  
**a.** **Offset aperture**  
The selection of migration parameters directly affects the migration running time and the resolution and signal-to-noise ratio of migration imaging. In migration, the migration aperture can be said to be the parameter that has the greatest impact on pre-stack depth migration imaging in addition to the depth domain velocity model. If the offset aperture is too small, the steep dip phase axis will be destroyed, the amplitude will change dramatically, and a large amount of random noise will be generated, which may lead to a false horizontal phase axis. When the migration aperture is too large, it will not only waste a lot of computing time and reduce the processing efficiency but also reduce the signal-to-noise ratio of the data. Deep noise affects shallow data, resulting in a decrease in the quality of migration imaging.  
For the same work area, it is best to use a unified migration aperture for the migration imaging of all survey lines so that the migration profile can maintain a unified amplitude characteristic. In practical applications, considering factors such as noise and target horizon, the selection of the migration aperture needs to be determined by experiments. The test  
Figure 11: Updating process of velocity model based on stretching correction. (**a-1**) azimuth attribute; (**a-2**) dip attribute; (**a-3**) event continuity attribute; (**b**) pencil database construction via model-based tomography; (**c-1**) flattening performance of CRP gather #185; (**c-2**) flattening performance of CRP gather #225; (**c-3**) flattening performance of CRP gather #337.  
results are shown in Figure 12. Taking the Inline80 line as an example, in the Inline direction, when the migration aperture is increased to 3000 m, the imaging quality of the steeply dipping formation is obviously improved, and the signal-to-noise ratio is relatively low. When it is increased to 3500 m, it has no effect on the imaging of inclined strata, but it brings more migration noise to shallow migration imaging. Therefore, it is determined that 3000 m is the best migration aperture in the Inline direction. In the Crossline direction, when the aperture increases to 2000 m, the imaging quality of the inclined formation is better, and the signal-to-noise ratio is relatively low. Therefore, 2000 m is the best migration aperture in the Crossline direction (see Figure 12).  
Anti-aliasing operatorThe Kirchoff integral method involves summing the discrete input data in time and space, without considering the frequency component of the data. Therefore, when the operator inclination angle of the offset summation trajectory is too steep or contains high frequency energy or the data space sampling is sparse, it is very easy for aliasing to appear, so it is necessary to carry out anti-aliasing filtering processing. The Inline80 line is still selected as an example, and the triangle accurate anti-aliasing method [33] is used. The anti-aliasing operators are 0.25, 1, and 2. The test results are shown in Figure 13. The imaging profiles of the three anti-aliasing factors show that the imaging results of the inclined strata are basically the same, and the signal-to-noise ratio of the shallow layer is relatively low. Because this processing uses a square grid of 10 m \(\times\) 10 m, and the sampling rate is high, the possibility of generating spatial aliasing is small, and a smaller anti-aliasing operator should be used. Therefore, the anti-aliasing operator is 0.25.