DESI (Dark Energy Spectroscopic Instrument) is a Stage IV ground-based dark
energy experiment that will study baryon acoustic oscillations (BAO) and the
growth of structure through redshift-space distortions with a wide-area galaxy
and quasar redshift survey. To trace the underlying dark matter distribution,
spectroscopic targets will be selected in four classes from imaging data. We
will measure luminous red galaxies up to $z=1.0$. To probe the Universe out to
even higher redshift, DESI will target bright [O II] emission line galaxies up
to $z=1.7$. Quasars will be targeted both as direct tracers of the underlying
dark matter distribution and, at higher redshifts ($ 2.1 < z < 3.5$), for the
Ly-$\alpha$ forest absorption features in their spectra, which will be used to
trace the distribution of neutral hydrogen. When moonlight prevents efficient
observations of the faint targets of the baseline survey, DESI will conduct a
magnitude-limited Bright Galaxy Survey comprising approximately 10 million
galaxies with a median $z\approx 0.2$. In total, more than 30 million galaxy
and quasar redshifts will be obtained to measure the BAO feature and determine
the matter power spectrum, including redshift space distortions.

DESI （暗能量光谱仪）是一项地基暗能量实验，将通过广阔的星系和类星体红移巡测研究声学波动和红移空间畸变的结构增长，以追踪基础暗物质的分布。