  SNO+ is a large-scale liquid scintillator experiment with the primary goal of
searching for neutrinoless double beta decay, and is located approximately 2 km
underground in SNOLAB, Sudbury, Canada. The detector acquired data for two
years as a pure water Cherenkov detector, starting in May 2017. During this
period, the optical properties of the detector were measured in situ using a
deployed light diffusing sphere, with the goal of improving the detector model
and the energy response systematic uncertainties. The measured parameters
included the water attenuation coefficients, effective attenuation coefficients
for the acrylic vessel, and the angular response of the photomultiplier tubes
and their surrounding light concentrators, all across different wavelengths.
The calibrated detector model was validated using a deployed tagged gamma
source, which showed a 0.6% variation in energy scale across the primary target
volume.
