## 3 Results
### Pluto 1.5 Model: Finite Difference Data  
In the deepwater basin of the Gulf of Mexico, the main feature is the development of thick layers of salt rocks in the Neogene to Middle Jurassic [45; 46]. Beneath large salt formations lies a target for oil and gas exploration. However, imaging below salt structures introduces the challenge of multiple reflections, leading to crosstalk artifacts. In order to simulate subsurface structures beneath salt more accurately, the Pluto 1.5 model (Figure 11) was utilized to validate the imaging efficacy of the proposed method for complex models. The Pluto 1.5 model is a publicly available geological model in geophysical community. It is derived from field exploration data and used for simulating primary and multiple wave signals beneath salt targets in the deepwater environment of the Gulf of Mexico [47]. Figure 11: Pluto 1.5 model: (**a**) P-wave velocity model; (**b**) density model. Figure 10: Downward wavefield illumination analysis of the single-frequency gradient term: (**a**) first iteration; (**b**) second iteration. The model consists of a series of sedimentary layers, several normal and thrust faults, and three large salt domes. Upon analyzing the velocity and density models, several velocity and density reversals have been identified within the sedimentary layers, accompanied by strong impedance interfaces at the top and bottom of the salt domes, the seabed layer, and free surface conditions. The model exhibits significant surface-related multiples and internal multiples. The model's original grid size (1201 \(\times\) 6960) was adjusted to 1201 \(\times\) 2501, with a horizontal spacing of 15.24 m and a vertical spacing of 7.62 m. There were 251 shots with a source spacing of 152.4 m, distributed across a range of 0-38 km. The source wavelet was a Ricker wavelet with a primary frequency of 15 Hz. The total recording time was 10 s, with a time sampling interval of 4 ms and 701 traces per shot, and a trace interval of 15.24 m. The source and the receiver depths were both at 7.62 m. Figure 12 displays the reflection data of this experiment, which have been modeled by an acoustic finite difference modeling scheme. Figure 12a shows the common-shot gather, while Figure 12b shows the common-offset gather. The black arrows indicate primaries. The solid white arrows and the dashed white arrows represent some surface-related multiples and internal multiples, respectively. The migration velocity model, shown in Figure 13, was obtained by Gaussian smoothing of the true velocity model (Figure 11a). Figure 12: Full-wavefield data of Pluto model computed with the finite difference method: (**a**) common-shot gather; (**b**) common-offset gather. The black arrow is primary wave, the solid white arrow is surface-related multiple, the dashed white arrow is internal multiple. Figure 13: Migration velocity model (Gaussian smoothing of the true velocity model). Three imaging conditions were applied to the full-wavefield data, producing migration results (Figure 14a-c). These migration results consistently demonstrate that the salt dome boundaries, sedimentary layers, and inclined faults possess comparable shallow imaging potentials. For the deep structures beneath the salt domes, which serve as strong shielding layers, the multi-order wavefield normalization imaging effect outperformed the other two conditions, providing enhanced deep illumination. Subsequently, we analyzed the multiple artifacts. The original data contain multiples, and the imaging is characterized by numerous interference artifacts. Among them, a shallow event nearly parallel to the seabed, marked by a white solid arrow extending from 1 to 2.5 km, is, in fact, a first-order surface-related multiple artifact associated with the seabed. Some unreasonable events are observed within the three salt domes, which are presumed to be caused by surface or internal multiples from the overlying layers.