And, when it is moving towards, the wave orthogonals can converge, or diverge which we have seen under the wave diffraction;and now, presence of obstructions like natural reefs, outcrops, for example, in India, tip of Indian peninsula you have so many outcrops; all these outcrops can lead to some kind of, will lead to some kind of diffraction; certain extent of diffraction; and, the presence of this, will also lead to some amount of refraction.