  We numerically calculate the reliability with which one can optically
determine the presence or absence of an individual scatterer in a randomly
occupied 3D array of well-localized, coherently radiating scatterers. The
reliability depends in a complicated way on the ratio of lattice spacing to
wavelength and the numerical aperture of the imaging system. The behavior can
be qualitatively understood by considering the dependence of Bragg scattering
modes on lattice spacing. These results are of interest for atomic
implementations of quantum information processing.
