This description is a copy of in [3]. The following definitions are used:

- , where is the wavelength at which the LSF is to be evaluated
- is the r.m.s. surface roughness for two scatter
models; is either
*small*or*large*for small angle scatter, and large angle scatter, respectively. This is available from CCF`LineSpreadFunc`. Note that the surface roughness for the large angle scatter is parameterized as a function of wavelength and its value is obtained with

`CAL_rgsGetLAScatterRoughness`(section 3.4.18) - is the correlation length of the scatter components;
is either
*small*or*large*for small angle scatter, and large angle scatter, respectively. This is available from CCF`LineSpreadFunc`. - is the center angle of the unscattered light distribution

The fraction of scattered light for small/large angle scatter is

with a correction factor of the LSF probability density for
large angle scattering of

where & are stored in CCF `LineSpreadFunc`, and
is defined by

The power spectral densities are defined with respect to , with

and finally the density functions for small and large angle scatter
are

The intensity of the LSF for one bin in that has a range from
to is then given by

where the total fraction of non-scattered light is given by
. The function
that is implemented in the CAL does not include the last term (the
-function), as is only the unscattered light and its
contribution is taken care of by the calling task (`rgsrmfgen`).

In order to obtain the LSF, this needs to be convolved with the PSF of the mirror, which acts as a perturbation of . This is not performed by this function.