  In this study, we evaluate a coronal mass ejection (CME) arrival prediction
tool that utilizes the wide-angle observations made by STEREO's heliospheric
imagers (HI). The unsurpassable advantage of these imagers is the possibility
to observe the evolution and propagation of a CME from close to the Sun out to
1 AU and beyond. We believe that by exploiting this capability, instead of
relying on coronagraph observations only, it is possible to improve today's CME
arrival time predictions. The ELlipse Evolution model based on HI observations
(ELEvoHI) assumes that the CME frontal shape within the ecliptic plane is an
ellipse, and allows the CME to adjust to the ambient solar wind speed, i.e. it
is drag-based. ELEvoHI is used to perform ensemble simulations by varying the
CME frontal shape within given boundary conditions that are consistent with the
observations made by HI. In this work, we evaluate different set-ups of the
model by performing hindcasts for 15 well-defined isolated CMEs that occurred
when STEREO was near L4/5, between the end of 2008 and the beginning of 2011.
In this way, we find a mean absolute error of between $6.2\pm7.9$ h and
$9.9\pm13$ h depending on the model set-up used. ELEvoHI is specified for using
data from future space weather missions carrying HIs located at L5 or L1. It
can also be used with near real-time STEREO-A HI beacon data to provide CME
arrival predictions during the next $\sim7$ years when STEREO-A is observing
the Sun-Earth space.
