  The PLANCK mission is the most sensitive all-sky CMB experiment currently
planned. The High Frequency Instrument (HFI) will be especially suited for
observing clusters of galaxies by their thermal Sunyaev-Zel'dovich (SZ) effect.
In order to assess PLANCKs SZ-capabilities in the presence of spurious signals,
a simulation is presented that combines maps of the thermal and kinetic
SZ-effects with a realisation of the cosmic microwave background (CMB), in
addition to Galactic foregrounds (synchrotron emission, free-free emission,
thermal emission from dust, CO-line radiation) as well as the sub-millimetric
emission from celestial bodies of our Solar system. Additionally, observational
issues such as the finite angular resolution and spatially non-uniform
instrumental noise of PLANCKs sky maps are taken into account, yielding a set
of all-sky flux maps, the auto-correlation and cross-correlation properties of
which are examined in detail. In the second part of the paper, filtering
schemes based on scale-adaptive and matched filtering are extended to spherical
data sets, that enable the amplification of the weak SZ-signal in the presence
of all contaminations stated above. The theory of scale-adaptive and matched
filtering in the framework of spherical maps is developed, the resulting filter
kernel shapes are discussed and their functionality is verified.
