The combination images of polarized intensity (above left) and polarization electric vector position angle (above right) are even more problematic to determine the expected noise statistics and diagnose problems for, as they involve ratios of Stokes images in the former and arc-tangents in the latter!

The quality of the polarization images will depend critically on the accuracy of the polarization calibration, where the instrumental cross-polarization terms (the so-called D-terms) are determined by observing a calibrator through a range of parallactic angles. For the VLA antennas and receiver systems, the polarization leakage (for example from RR to RL) is a few percent, on the order of the true polarized intensity fraction of most target objects.