Sub bottom imaging. A technique using multi-beam, low frequency sonars combined with synthetic aperture sonar software to generate a fully three-dimensional view of the layers of sediment or rock under the seabed. SBI can be used for detecting and classifying buried objects (such as unexploded ordinance, underwater explosive mines, buried pipelines or buried cables). SBI provides superior resolution and a full 3D image compared to the lower-resolution and 2D profile of an SBP