Subcritical penetration of narrow Gaussian beams into sediments

Complete wave-theory solutions have been obtained numerically for both the reflected and the transmitted fields associated with a narrow Gaussian beam incident on a water–sediment interface near the critical grazing angle. Interesting reflectivity phenomena are observed, such as subcritical beam penetration into the sediment, nonspecular beam reflection, and lateral displacement along the interface of both the reflected and the transmitted beams. These results are in qualitative agreement with experimental observations using parametrically (nonlinearly) generated beams. It is demonstrated, however, that the fundamental reflectivity characteristics of narrow beams can be entirely explained within the framework of linear acoustics.