  We analyze the detection capability of Coronal Mass Ejections (CMEs) for all
currently operating coronagraphs in space. We define as CMEs events that
propagate beyond 10 solar radii with morphologies broadly consistent with a
magnetic flux rope presence. We take advantage of multi-viewpoint observations
over five month-long intervals, corresponding to special orbital configurations
of the coronagraphs aboard the STEREO and SOHO missions. This allows us to sort
out CMEs from other outward-propagating features (e.g. waves or outflows), and
thus to identify the total number of unique CMEs ejected during those periods.
We determine the CME visibility functions of the STEREO COR2-A/B and LASCO
C2/C3 coronagraphs directly as the ratio of observed to unique CMEs. The
visibility functions range from 0.71 to 0.92 for a 95% confidence interval. By
comparing detections between coronagraphs on the same spacecraft and from
multiple spacecraft, we assess the influence of field of view, instrument
performance, and projection effects on the CME detection ability without
resorting to proxies, such as flares or radio bursts. We find that no major
CMEs are missed by any of the coronagraphs, that a few slow halo-like events
may be missed in synoptic cadence movies and, that narrow field of view
coronagraphs have difficulties discriminating between CMEs and other ejections
leading to false detection rates. We conclude that CME detection can only be
validated with multi-viewpoint imaging-- two coronagraphs in quadrature offer
adequate detection capability. Finally, we apply the visibility functions to
observed CME rates resulting in upward corrections of 40%.
