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The Effect of Strong Near Surface Scattering on Seismic Imaging: Investigation Based on Resolution Analysis

. In land seismic exploration, strong near-surface heterogeneities can cause serious problems in seismic data acquisition and the quality of depth imaging. By introducing random velocity models to simulate velocity ﬂuctuations in the near-surface layer and using the point spread function to characterize image quality, we examine how the scattering generated in near-surface heterogeneities can affect the subsurface image. In addition to the commonly known scattering noises which lower the signal to noise ratio in seismic data, our results also reveal that intermediate scale heterogeneities generate forward scattering which forms phase or travel time ﬂuctuations. Due to intermediate-scale uncertainty in the shallow part of the migration velocity model, these phase changes are carried to the target by the extrapolated waveﬁelds, breaking the zero phase image condition at the image point. This is a primary reason for deteriorated image quality in regions with strong near-surface scattering. If this intermediate-scale information can be obtained and built into the migration velocity, the subsurface image quality can be largely improved. These results can be the ba-sis for further numerical investigations and ﬁeld experiments. The proposed analysis method can also be used to evaluate other potential methods for dealing with near-surface scattering. in point spread function, and the quality of depth image. Our investigation indicated that, if high resolution velocities down to 100-300 m scale can be built into the near surface migration velocity model, the phase errors can be largely removed and the image quality can be signiﬁcantly improved. It is possible using current acquisition density for imaging and the corresponding near-surface velocity inversion techniques to build velocity models with such accuracy. Most existing methods attempt to suppress scattering through stacking and ﬁltering, which should be effective for reducing the random noise. However, coherent phase errors should be compensated using high precision migration velocity mode. The current numerical simulations were conducted in a constant density acoustic media under the 2D geometry, and no free surface condition was used. Further studies may be extended to more realistic situations, e.g., elastic model, 3D scattering, and using random velocity parameters based on local near surface velocity structures.