Data levels

A data level labels how far a file has been processed through the reduction pipeline. It is the first argument to almost every query method (e.g. query_datetime('l2', ...)) and it picks which underlying table you search, so getting it right is the first decision you make.

Frame it as one question: how processed do you need the data to be?

Level	What it contains	Who wants it
L0	Raw 2D detector frames, straight off the CCD	Only if you run your own reduction
L1	Calibrated, wavelength-solved 1D extracted spectra	Custom spectral / line / activity analysis
L2	RV-ready products: the CCF and the radial velocity	Most science users
eng (engineering level)	Engineering / calibration frames	Instrument debugging only

Levels map to tables

Each archive maps its data_level strings to its own server tables (for example, NEID’s 'l2' is the table neidl2). You pass the level string, never the table name; the package translates for you, and archive.data_levels lists the levels an archive offers.

The solar variants

Archives with a solar feed mirror the same hierarchy for Sun-as-a-star data, with levels named solarl0, solarl1, solarl2, and so on. An archive may offer only some levels; each archive’s page has its table of levels.

Practical default

Start with the level that holds the radial velocities — 'l2', or 'solarl2' for solar data — since that is what most users came for. Drop to 'l1' only when you want the spectra themselves, and to 'l0' only when you intend to reduce raw frames yourself.

Once you have picked a level, see Choosing a query for picking the query method.