  We investigate the observability of higher harmonics in gravitational wave
signals emitted during the coalescence of binary black holes. We decompose each
mode into an overall amplitude, dependent upon the masses and spins of the
system, and an orientation-dependent term, dependent upon the inclination and
polarization of the source. Using this decomposition, we investigate the
significance of higher modes over the parameter space and show that the $\ell =
3$, $m = 3$ mode is most significant across much of the sensitive band of
ground-based interferometric detectors, with the $\ell = 4$, $m = 4$ having a
significant contribution at high masses. We introduce the higher mode
signal-to-noise ratio (SNR), and show that a simple threshold on this SNR can
be used as a criterion for observation of higher harmonics. Finally, we
investigate observability in a population of binaries and observe that higher
harmonics will only be observable in a few percent of binaries, typically those
with unequal masses and viewed close to edge-on.
