Knott's equations

In geophysics, Knott's equations were the first equations to describe the amplitudes of reflected and refracted waves generated at non-normal incidence upon an interface.^[1] They were derived in 1899 by the British geophysicist Cargill Gilston Knott using displacement potential functions^[2] and describe the same phenomenon that the Zoeppritz equations describe in terms of amplitude displacements.

Diagram showing the mode conversions that occur when a P-wave reflects off an interface at non-normal incidence