The origin of spectral features, speckle effects, is explained, followed by a discussion on many aspects of spectral
features generation. The next part gives an overview of means to limit the amplitude of the spectral features. This paper
gives a discussion of all means to reduce the spectral features amplitude (SFA), i.e. inner pixel averaging, coherence
effects, and angular averaging, and to a lesser extend coherence effects and polarization. A new approach to model
spectral features is presented, that is based on the averaging mechanisms, in a similar way as is used for speckle patterns.
Formulae for all averaging methods are given and the use is discussed. The paper starts off with a short description on
Spectral Features as observed in earth observation spectrometers, followed by speckle effects and averaging
mechanisms. Next the origin of the averaging mechanisms in a spectrometer are given and a method to calculate them.