Compute the Rayleigh scattering coefficient of air.

When default values are used, this provides the Rayleigh scattering coefficient for air at 550 nm in standard temperature and pressure conditions.

The scattering coefficient is computed by considering the air as a pure gas with associated effective optical properties (refractive index, King factor) and according to the expression provided by [Ebe10] (eq. 60):

$k_{\mathrm s \, \lambda} (n) = \frac{8 \pi^3}{3 \lambda^4} \frac{1}{n} \left( \eta_{\lambda}^2(n) - 1 \right)^2 F_{\lambda}$

where $$\lambda$$ is the wavelength (subscript indicates spectral dependence), $$n$$ is the air number density, $$\eta$$ is the air refractive index and $$F$$ is the air King factor.

The King correction factor is computed by linearly interpolating the data from [Bat84].

Parameters
Returns

quantity – Scattering coefficient.