tracking the sky, spectroscopically

At group meeting today, Blanton spoke at length about telluric corrections and sky subtraction in the various spectroscopic surveys that make up SDSS-IV. His feeling is that the number of sky and telluric-standard fibers assigned in the surveys might not be optimal given the variability of the relevant systematics. He enlisted our help in analyzing that situation. In particular, what model complexity does the data support? And, given that model complexity, what is the best sampling of the focal plane with telluric standards (and sky fibers)? I agreed to write down some ideas for the SDSS-IV mailing lists.