T. L. Duvall Jr., A. G. Kosovichev, and P. H. Scherrer 

Sunspots: Frontside and Backside Measurements with Time-Distance Helioseismology

In time-distance helioseismology, travel times measured between 
different surface locations are used to infer subsurface flows,
temperature inhomogeneities and magnetic fields.  
It has been suggested that most of the 
travel time reduction near sunspots may be due to the lowered
reflection layer associated with the Wilson depression.  This will
be examined by looking at rays that travel below the sunspot 
but do not begin or end in the spot.  A time-distance method
of imaging sunspots on the backside will be compared with that
of Lindsey and Braun.