The Dark Energy Spectroscopic Instrument (DESI) is under construction to measure the
expansion history of the Universe using the Baryon Acoustic Oscillation technique.
The spectra of 35 million galaxies and quasars over 14000 sq deg will be measured
during the life of the experiment. A new prime focus corrector for the KPNO Mayall
telescope will deliver light to 5000 fiber optic positioners. The fibers in turn feed
ten broad-band spectrographs. We report progress on a predictive sky background model
for DESI, built on the spectra from the 5-year Baryon Acoustic Oscillation Spectroscopic
Survey (BOSS). This dataset consists of 1 million unique sky spectra covering 360
- 1040 nm collected in a variety of observational conditions. Using a fitted profile
of the line spread function from the BOSS spectrograph, we separate the background
continuum flux from the airglow lines, allowing us to study the behavior of both distinct
emission sources across a large parameter space. Including both dark and bright sky
conditions and covering the majority of the 24th solar cycle, our analysis provides
new measurements of the inter-line sky continuum. The analysis of this paper is limited
to the continuum flux in dark sky conditions at several wavelengths. This improved
spectroscopic sky background model can be used in simulations and forecasting for
DESI and other surveys.
