Studies of the Linearity of the ATLAS EM Barrel Calorimeter

The ATLAS experiment uses an accordion shaped lead/liquid argon sampling calorime- ter for electromagnetic calorimetry. During beam test campaigns in summer 2002 and summer 2004 dedicated linearity scans were carried out. During the 2004 run, not only the beam energy but also the material in front of the calorimeter has been varied. This contribution discusses methods to achieve an excellent linearity and resolution even in the presence of a significant amount of upstream material. These methods were developed and tested on data obtained from the described beam tests and on a Geant4 simulation of the beam test setup.