Why do refracted waves not give us good accuracy? What is the technique of refraction method realization?
As the angle of incidence increases, more wave energy is converted into refracted waves. So, refraction represents waves that are approaching obliquely to an interface, and then travelling along the interface. Of course, some energy is transmitted into the layer below, too (perhaps at various small anaomalies along the layer interface?). Some of that energy can then reflect off the base of the layer, and return towards shallower depths. The drawing shows some of the raypaths in such a system. The key issue is that there are many possible raypaths. These can lead to the reception of the initial seismic pulse at a wide range of times in each long-offset receiver. It can be very difficult, or impossible, to decipher which raypath was taken (we only have time of reception, not history). The places wehere refraction is most useful are those with a major velocity difference, and where the geometry of the layers is fairly simple. Refraction can be useful in evaluating the near-surface soil la
