What type of reflection occurs at a large, smooth boundary?

Specular reflection occurs at large, smooth boundaries, such as a calm body of water or a well-polished surface. In specular reflection, the angle of incidence is equal to the angle of reflection, which means that when the ultrasound waves strike a smooth surface, they reflect back in a well-defined, predictable direction. This quality of specular reflection is crucial in ultrasound imaging, as it enables clear and distinct images of structures.

In contrast, other types of reflection do not provide the same clarity or directionality for imaging purposes. For example, diffuse reflection happens when light strikes a rough or uneven surface, causing the light rays to scatter in many directions. This leads to a loss of image resolution. Scattered reflection also results from irregularities in a boundary but can involve multiple angles and directions. Random reflection refers to any reflection that is not organized, contributing further to blurred or indistinct imaging. Thus, the characteristics of specular reflection are essential for achieving optimal results in sonographic imaging, making it the correct choice for this question.