Assessment of the method used to construct clearness index maps for the new european solar radiation atlas (ESRA).

We present an assessement of the methods used to construct maps for a new Solar Radiation Atlas for Europe. For this atlas station data and satellite derived data are used in an interpolation/merging process to derive maps of the long term monthly global radiation that cover an area ranging from 30\degre W to 70\degre E and from 25\degre to 75\degre N. Our focus is on the discussion of the accuracy of the method applied - a co-kriging technique. Special emphasis is put on the discussion whether the use of satellite derived radiation maps with a low spatial resolution brings benefits.