Reflections may occur in a number of wave and particle phenomena; these include [[acoustics|acoustic]] (as in common echos and underwater [[sonar]]), seismic waves in geologic structures, surface waves in bodies of water, and various electromagnetic waves, most usefully from [[Very high frequency|VHF]] and higher radar frequencies, progressing upward through centimeter to millimeter-wavelength [[radar]] and the various [[light]] frequencies and (with special "grazing" mirrors, to [[X-ray]] frequencies and beyond to [[gamma ray]]s. | Reflections may occur in a number of wave and particle phenomena; these include [[acoustics|acoustic]] (as in common echos and underwater [[sonar]]), seismic waves in geologic structures, surface waves in bodies of water, and various electromagnetic waves, most usefully from [[Very high frequency|VHF]] and higher radar frequencies, progressing upward through centimeter to millimeter-wavelength [[radar]] and the various [[light]] frequencies and (with special "grazing" mirrors, to [[X-ray]] frequencies and beyond to [[gamma ray]]s. |