“…Note that (25) equation, as we saw earlier, is an equation for the specific intensity, which is a 'phase-space' quantity. Wigner transforms serve as a bridge to link these two quantities (Yoshimori, 1998;Friberg, 1986;Marchand & Wolf, 1974;Pederson & Stamnes, 2000). We introduce the Wigner transforms of waves and Green's functions as…”