  Scalar features in time-dependent fluid flow are traditionally visualized
using 3D representation, and their topology changes over time are often
conveyed with abstract graphs. Using such techniques, however, the structural
details of feature separation and the temporal evolution of features undergoing
topological changes are difficult to analyze. In this paper, we propose a novel
approach for the spatio-temporal visualization of feature separation that
segments feature volumes into regions with respect to their contribution to
distinct features after separation. To this end, we employ particle-based
feature tracking to find volumetric correspondences between features at two
different instants of time. We visualize this segmentation by constructing mesh
boundaries around each volume segment of a feature at the initial time that
correspond to the separated features at the later time. To convey temporal
evolution of the partitioning within the investigated time interval, we
complement our approach with spatio-temporal separation surfaces. For the
application of our approach to multiphase flow, we additionally present a
feature-based corrector method to ensure phase-consistent particle
trajectories. The utility of our technique is demonstrated by application to
two-phase (liquid-gas) and multi-component (liquid-liquid) flows where the
scalar field represents the fraction of one of the phases.
