  Time delay and velocity estimation has been a widely studied subject in the
context of signal processing, with applications in many different fields of
physics. The velocity of fluctuation structures is typically estimated as the
distance between two measurement points divided by the time lag that maximizes
the cross-correlation function between the measured signals. In this
contribution, we demonstrate that this technique is not suitable in two spatial
dimensions unless the velocity is aligned with the separation between the
measurement points. We present an improved method to accurately estimate both
components of the velocity vector relying on three non-aligned measurement
points. The cross-correlation based three-point time delay method is shown to
give exact results for the velocity components in the case of a super-position
of uncorrelated Gaussian pulses. The new technique is tested on synthetic data
generated from realizations of such processes for which the underlying velocity
components are known. The results are compared with and found vastly superior
to those obtained using the standard two-point technique. Finally, we
demonstrate the applicability of the three-point method on gas puff imaging
data of strongly intermittent plasma fluctuations at the boundary of the
Alcator C-Mod tokamak.
