  If stationary, the spectrum of vacuum field noise (VFN) is an important
ingredient to get information about the curvature invariants of classical
worldlines (relativistic classical trajectories). For scalar quantum field
vacua there are six stationary cases as shown by Letaw some time ago, these are
reviewed here. However, the non-stationary vacuum noises are not out of reach
and can be processed by a few mathematical methods which I briefly comment on.
Since the information about the kinematical curvature invariants of the
worldlines is of radiometric origin, hints are given on a more useful
application to radiation and beam radiometric standards at relativistic
energies
