  The physical structures of the outer atmospheres of red giants are not known.
They are certainly complex and a range of recent observations are showing that
we need to embrace to non-classical atmosphere models to interpret these
regions. This region's properties is of importance, not the least, for the
understanding of the mass-loss mechanism for these stars, which is not still
understood. Here, we present observational constraints of the outer regions of
red giants, based on mid-IR, high spectral resolution spectra. We also discuss
possible non-LTE effects and highlight a new non-LTE code that will be used to
analyse the spectra of these atmospheric layers. We conclude by mentioning our
new SOFIA/EXES observations of red giants at 6 microns, where the
vibration-rotation lines of water vapour can be detected and spectrally
resolved for the first time.
