  Velocity measurements made from multiple-epoch astronomical images of
evolving objects with optically thin continuum emission (e.g. as relativistic
jets or expanding supernova shells) may be confused as a result of the overlap
of semi-transparent features moving at different speeds. Multi-scale wavelet
decomposition can be effectively applied to identify and track such overlapping
features, provided that their respective structural responses can be separated
over the spatial scales used for the decomposition. We developed a new method
that combines the stacked cross-correlation with the wavelet-based image
segmentation and evaluation (WISE) technique of decomposition of
two-dimensional structures, to separate and track dominant spatial responses of
overlapping evolving features. The method is tested on a set of simulated
images of a stratified relativistic jet, demonstrating the robust detection of
both the faster spine and the slower sheath speeds. The method is applied to
mutliple-epoch images from the MOJAVE survey, revealing two different
superluminal streams inside the jet in 3C 273 and the acceleration of the flow
in 3C 120. The method can be applied to densely monitored objects with
composite structural evolution such as the parsec-scale jet in M87 or heavily
resolved expanding supernova shells.
