Space-time-frequency moment densities
David H. Hughes, Bruce W. Suter · Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 2002
The frequency operator, Ω equivalent to i (partial derivative) δ/δt, is not necessarily Hermitian when acting on nonstationary signals. Central moment densities of Ω and its conjugate, temporal operator Τ, are proportional to the real parts of local central moments derived from the Wigner distribution. A nonrelativistic space-time-frequency Wigner distribution forms the backdrop and motivation for the present investigation.