The variable RAA defines the Relative solar Azimuth Angle (in [deg] East of North), i.e., the angle between two vertical planes at the reference point, one containing the line-of-sight and the second containing the solar illumination path. Its value varies between 0 deg to 360 deg, with a default value of 45 deg.
This variable defines the geometry of the sun-target-sensor optical path, which increases/decreases the effects of scattering caused by aerosols.