We have developed a technique to construct a spectro-polarimetrically accurate
magneto-hydrostatic model of a large-scale solar magnetic field concentration,
mimicking a sunspot. Using the developed model, we simulate observational signatures of acoustic wave propagation, conversion and absorption in the solar interior and photosphere with the sunspot embedded into it. With the 6173A magnetically sensitive photospheric absorption line of neutral iron, we have calculated observable quantities such as continuum intensities, Doppler velocities, as well as full Stokes vector for the simulation at various positions at the solar disk. We will demonstrate the influence of systematic effects induced by non-locality of radiative transport in the solar photosphere on helioseismic measurements.