  We investigate the accuracy to which we can retrieve the solar photospheric
magnetic field vector using the Helioseismic and Magnetic Imager (HMI) that
will fly onboard of the Solar Dynamics Observatory (SDO) by inverting simulated
HMI profiles. The simulated profiles realistically take into account the
effects of the photon noise, limited spectral resolution, instrumental
polarization modulation, solar p modes and temporal averaging. The accuracy of
the determination of the magnetic field vector is studied considering the
different operational modes of the instrument.
