Our galaxy absorption could significantly decrease the signal of a distant source depending mostly on the galactic latitude.
Generally the transmission of our galaxy is define as function of wavelength as
trans_gal = 10**(-0.4*A(lambda, alpha,delta))
where A is the absorption and depend on the wavelength and the source coordinate on the sky.
See Schlegel 1998, Jouvel 2011 and Zoubian in prep for more details.
A very convenient way to implement that is to ask to the user to provide the spectra A(lambda) or directly trans_gal(lambda) for a given (alpha,delta).
Then you have just apply the transmission on the signal.
Note that the sky background like zodiacal light is not affect by this absorption.