  We experimentally investigate the influence of the orientation of optically
pumped magnetometers in Earth's magnetic field. We focus our analysis to an
operational mode that promises femtotesla field resolu-tions at such field
strengths. For this so-called light-shift dispersed Mz(LSD-Mz) regime, we focus
on the key parameters defining its performance. That are the reconstructed
Larmor frequency, the transfer function between output signal and magnetic
field amplitude as well as the shot noise limited field resolution. We
demonstrate that due to the use of two well balanced laser beams for optical
pumping with different helicities the heading error as well as the field
sensitivity of a detector both are only weakly influenced by the heading in a
large orientation angle range.
