DESI is for dark energy spectroscopic instrument and will measure the effect of dark energy on the expansion of universe. It will obtain optical spectra for tens of millions of galaxies and quasars, constructing a 3D map spanning the nearby universe to 11 billion light years.
The DESI survey is being conducted on the mayall 4-meter telescope at kitt peak national observatory. DESI is supported by the department of energy office of science to perform this stage IV dark energy measurement using baryon acoustic oscillations and other techniques that rely on spectroscopic measurements.
DESI's scientific goal is to constrain possible models of dark energy.