The overall version number of the throughputs repo is tied to the
version number of lsst-pst/syseng_throughputs which is the
source of the Rubin/LSST throughput curves. Major/minor updates match
the version number there.
Patch updates here indicate changes in throughputs curves other than the
LSST curves, such as adding more reference bandpasses from other surveys.
This repository contains reference throughput curves from various surveys (Megacam, WISE, SDSS, Johnson UBV and various other telescopes), together with the expected performance throughput curves for LSST.
The LSST throughput curves are in baseline, with more information on the curves available there in that README.md. If you are only concerned with calculating expected magnitudes for LSST in various bandpasses, then you should use the 'baseline' throughputs.
The files in 'phosim' are related to the throughputs used in the phosim simulations. The 'goal' directory holds the throughputs used as goals for phosim development at the time of tagging (of this SVN directory), and the 'actual' directory holds the phosim actual throughputs, at the time of the simulations. These have not been updated since 2010, but are preserved for historical purposes.
The directory 'atmos' contains various airmass atmospheres, both without and with (the files ending with _aerosol.dat) aerosols.
More information is available in README files within each directory.