  The effects of acoustic wave absorption, mode conversion and transmission by
a sunspot on the helioseismic inferences are widely discussed, but yet
accounting for them has proved difficult for lack of a consistent framework
within helioseismic modelling. Here, following a discussion of problems and
issues that the near-surface magnetohydrodynamics hosts through a complex
interplay of radiative transfer, measurement issues, and MHD wave processes, I
present some possibilities entirely from observational analyses based on
imaging spectropolarimetry. In particular, I present some results on wave
evolution as a function of observation height and inclination of magnetic field
to the vertical, derived from a high-cadence imaging spectropolarimetric
observation of a sunspot and its surroundings using the instrument IBIS
(NSO/Sac Peak, USA). These observations were made in magnetically sensitive (Fe
I 6173 A) and insensitive (Fe I 7090 A) upper photospheric absorption lines.
Wave travel time contributions from within the photospheric layers of a sunspot
estimated here would then need to be removed from the inversion modelling
procedure, that does not have the provision to account for them.
