These scattering source functions are^{20}^{,}^{21}Display Formula
$Fr+(\theta ,\varphi ,z)=1\theta [\u222b02\pi \u222b01Pr(\theta ,\varphi ;\theta \u2032,\varphi \u2032)Ir+(\theta \u2032,\varphi \u2032,z)d\theta \u2032d\varphi \u2032+\u222b02\pi \u222b01Pr(\theta ,\varphi ;\u2212\theta \u2032,\varphi \u2032)Ir\u2212(\u2212\theta \u2032,\varphi \u2032,z)d\theta \u2032d\varphi \u2032],$(6)
Display Formula$Fr\u2212(\u2212\theta ,\varphi ,z)=1\theta [\u222b02\pi \u222b01Pr(\u2212\theta ,\varphi ;\theta \u2032,\varphi \u2032)Ir+(\theta \u2032,\varphi \u2032,z)d\theta \u2032d\varphi \u2032+\u222b02\pi \u222b01Pr(\u2212\theta ,\varphi ;\u2212\theta \u2032,\varphi \u2032)Ir\u2212(\u2212\theta \u2032,\varphi \u2032,z)d\theta \u2032d\varphi \u2032],$(7)
where $Pr(\theta ,\varphi ;\theta \u2032,\varphi \u2032)$ is the phase matrix and describes the scattering property from direction $(\theta \u2032,\varphi \u2032)$ into direction $(\theta ,\varphi )$.