Refinements of a classical technique of airglow spectroscopy

We have performed ground-based airglow observations with a tilting filter spectrometer to determine ro-tational temperatures in the mesopause region since 1984. Although quite simple in principle, the success of the technique depends on a number of non-trivial details, including corrections for measurements under less favorable conditions, as, for instance, full moon nights. Successive improvements have finally led to nearly continuous observations, since August 1997, with more than 200 nights of useful data per year. The technique is described in some detail and recent results are discussed