  A new method for calibrating the hadron response of a segmented calorimeter
is developed and successfully applied to beam test data. It is based on a
principal component analysis of energy deposits in the calorimeter layers,
exploiting longitudinal shower development information to improve the measured
energy resolution. Corrections for invisible hadronic energy and energy lost in
dead material in front of and between the calorimeters of the ATLAS experiment
were calculated with simulated Geant4 Monte Carlo events and used to
reconstruct the energy of pions impinging on the calorimeters during the 2004
Barrel Combined Beam Test at the CERN H8 area. For pion beams with energies
between 20 GeV and 180 GeV, the particle energy is reconstructed within 3% and
the energy resolution is improved by between 11% and 25% compared to the
resolution at the electromagnetic scale.
