 Scattering phase function

A scattering phase function describes the angular distribution of single-scattered power. One common convention is $\int Pd\Omega =4\pi$, so that $P/(4\pi )$ is a probability density over outgoing solid angle. For unpolarized Rayleigh scattering, $P=3(1+{\cos }^2\Theta )/4$. It is distinct from the oscillatory-integral meaning of phase function.