The study of GeV and TeV gamma-ray emission from galactic sources such as supernova remnants (SNR) may provide key insights into their potential role as accelerators of cosmic rays up to the knee (10^15 eV). Emission from these types of sources can be spatially extended, with a complex morphology that depends on energy. It is particularly interesting to establish the degree to which colocated extended gamma-ray sources detected by Fermi and by ground-based TeV gamma-ray instruments (such as the VERITAS Observatory) share structure.

However, establishing such correlations can be quite difficult, as detections of more diffuse sources are more likely to be photon statistics-limited (particularly true for Fermi detections above 10 GeV) and the significance of any substructure marginal. We report here on preliminary studies of a likelihood-based method for establishing correlation, using simulated Fermi and VERITAS observations of spatially extended sources.