  Highly-multiplexed, robotic, fiber-fed spectroscopic surveys are observing
tens of millions of stars and galaxies. For many systems, accurate positioning
relies on imaging the fibers in the focal plane and feeding that information
back to the robotic positioners to correct their positions. Inhomogeneities and
turbulence in the air between the focal plane and the imaging camera can affect
the measured positions of fibers, limiting the accuracy with which fibers can
be placed on targets. For the Dark Energy Spectroscopic Instrument, we
dramatically reduced the effect of turbulence on measurements of positioner
locations in the focal plane by taking advantage of stationary positioners and
the correlation function of the turbulence. We were able to reduce positioning
errors from 7.3 microns to 3.5 microns, speeding the survey by 1.6% under
typical conditions.
