  As the 3D spatial properties of exoplanet atmospheres are being observed in
increasing detail by current and new generations of telescopes, the modelling
of the 3D scattering effects of cloud forming atmospheres with inhomogeneous
opacity structures becomes increasingly important to interpret observational
data. We model the scattering and emission properties of a simulated cloud
forming, inhomogeneous opacity, hot Jupiter atmosphere of HD 189733b. We
compare our results to available HST and Spitzer data and quantify the effects
of 3D multiple-scattering on observable properties of the atmosphere. We
discuss potential observational properties of HD 189733b for the upcoming TESS
and CHEOPS missions. We develop a Monte Carlo radiative transfer code and apply
it to post-process output of our 3D radiative-hydrodynamic, cloud formation
simulation of HD 189733b. We employ three variance reduction techniques; next
event estimation, survival biasing and composite emission biasing to improve
signal-to-noise of the output.For cloud particle scattering events, a
log-normal area distribution is constructed from the 3D cloud formation RHD
results and stochastically sampled in order to model the Rayleigh and Mie
scattering behaviour of a mixture of grain sizes. Stellar photon packets
incident on the eastern dayside hemisphere show predominantly Rayleigh,
single-scattering behaviour, while multiple-scattering occurs on the western
hemisphere. Combined scattered and thermal emitted light predictions are
consistent with published HST and Spitzer secondary transit observations. Our
model predictions are also consistent with geometric albedo constraints from
optical wavelength ground based polarimetry and HST B-band measurements. We
predict an apparent geometric albedo for HD 189733b of 0.205 and 0.229, in the
TESS and CHEOPS photometric bands respectively.
