1. A metrology method, comprising the steps of: measuring, with an overlay scatterometry metrology tool, a signal from each of a plurality of targets across a range of at least one measurement parameter; identifying, with one or more processors, an inaccuracy contribution of at least one process variation source to the measured scatterometry signal; and extracting, with the one or more processors, a measurement variability over a range indicative of the inaccuracy contribution by modeling, with the one or more processors, a per-pixel measured overlay response to target imperfections based on per-pixel measured overlay deviations and measurement of multiple overlay targets.