  The Solar TErrestrial RElations Observatory (STEREO) and its heliospheric
imagers (HI) have provided us the possibility to enhance our understanding of
the interplanetary propagation of coronal mass ejections (CMEs). HI-based
methods are able to forecast arrival times and speeds at any target and use the
advantage of tracing a CME's path of propagation up to 1 AU. In our study we
use the ELEvoHI model for CME arrival prediction together with an ensemble
approach to derive uncertainties in the modeled arrival time and impact speed.
The CME from 3 November 2010 is analyzed by performing 339 model runs that are
compared to in situ measurements from lined-up spacecraft MESSENGER and
STEREO-B. Remote data from STEREO-B showed the CME as halo event, which is
comparable to an HI observer situated at L1 and observing an Earth-directed
CME. A promising and easy approach is found by using the frequency
distributions of four ELEvoHI output parameters, drag parameter, background
solar wind speed, initial distance and speed. In this case study, the most
frequent values of these outputs lead to the predictions with the smallest
errors. Restricting the ensemble to those runs, we are able to reduce the mean
absolute arrival time error from $3.5 \pm 2.6$ h to $1.6 \pm 1.1$ h at 1 AU.
Our study suggests that L1 may provide a sufficient vantage point for an
Earth-directed CME, when observed by HI, and that ensemble modeling could be a
feasible approach to use ELEvoHI operationally.
