Modelling the UV/optical - infrared/submm SEDs of spiral galaxies
observed with Herschel will be an essential tool to quantitatively
interpret these observations in terms of the present and past
star-formation activity of these systems.
In this lecture we describe the SED modelling technique we have
developed, its applications and tests of its predictions. We show
that both the panchromatic SED modelling of individual galaxies and the
B-band attenuation-inclination relation of
large statistical samples suggest that spiral galaxies in the nearby Universe
behave as optically thick systems in their global properties and large-scale
distribution of light (central face-on B-band opacity of τBf~4).
However disk galaxies are very
inhomogeneous systems, having both optically thick components (e.g. spiral
arms), and optically thin components (e.g. the interarm regions), the latter
making galaxies transparent to background galaxies.