  We describe the implementation of a robotic SLODAR instrument at the Cerro
Paranal observatory. The instrument measures the vertical profile of the
optical atmospheric turbulence strength, in 8 resolution elements, to a maximum
altitude ranging between 100 m and 500 m. We present statistical results of
measurements of the turbulence profile on a total of 875 nights between 2014
and 2018. The vertical profile of the ground layer of turbulence is very
varied, but in the median case most of the turbulence strength in the ground
layer is concentrated within the first 50 m altitude, with relatively weak
turbulence at higher altitudes up to 500 m. We find good agreement between
measurements of the seeing angle from the SLODAR and from the Paranal DIMM
seeing monitor, and also for seeing values extracted from the Shack-Hartmann
active optics sensor of VLT UT1, adjusting for the height of each instrument
above ground level. The SLODAR data suggest that a median improvement in the
seeing angle from 0.689 arcsec to 0.481 arcsec at wavelength 500 nm would be
obtained by fully correcting the ground-layer turbulence between the height of
the UTs (taken as 10 m) and altitude 500 m.
