  Using Doppler velocity data from the SOI/MDI instrument onboard the SoHO
spacecraft, we do time-distance helioseismic inversions for sound-speed
perturbations beneath 16 sunspots observed in high-resolution mode. We clearly
detect ring-like regions of enhanced sound speed beneath most sunspot
penumbrae, extending from near the surface to depths of about 3.5 Mm. Due to
their location and dependence on frequency bands of p-modes used, we believe
these rings to be artifacts produced by a surface signal probably associated
with the sunspot magnetic field.
