Fig. 4: Hydrodynamic shock velocity analysis comparing simulation and experiment.
From: Multi-messenger dynamic imaging of laser-driven shocks in water using a plasma wakefield accelerator

The velocity measurement tracks the point of highest density in FLASH, and the minimum intensity feature in both synthetic and experimental phase-contrast X-ray images. The error bars of ± 4 μm in the experimental shock position reflect the spatial resolution of the imaging system, and consider the previous edge calibration with simulation density.