Default $DESI_ROOT/spectro/data

DESI_SPECTRO_DATA contains raw data as produced by the telescope. The canonical location is $DESI_ROOT/spectro/data, but one can set the environment variable DESI_SPECTRO_DATA to point anywhere. The exposures are grouped by night as a YEARMMDD string. The “night” roles over at noon local time, so all data taken between sunset and sunrise belong to the same night (i.e. the date of the sunset). Under each night, data are grouped in subdirectories by exposure ID (zero-padded 8-digit).