  Surface preparation of niobium superconducting RF cavities is a critical step
for achieving good RF performance under the superconducting state. Surface
defect, roughness, and contamination affect the accelerating gradient and
quality factor of the cavities. We report surface inspection methods used to
control the surface processing of 650 MHz cavities designated for the
pre-production and prototype cryomodules for PIP-II linac. The cavity surface
was routinely inspected visually, with an optical camera, and by microscopic
scanning of surface replicas. This article covers details on the surface
inspection methods and surface polishing process used to repair the surface.
