LEFT:  Carrington map of UVCS H I Lyman alpha intensity, observed
in October and November 1999 when an equatorial coronal hole was
rotating by the east solar limb.  The dark patch in the center of
the image represents the equatorial coronal hole.

RIGHT:  An empirical reconstruction of the same time period and
spectral line as plotted on the left.  A three-dimensional empirical
model of the plasma properties in the equatorial coronal hole (and
in the brighter surrounding plasma) was used as input to a 
spectral line synthesis code that integrated along the optically
thin line of sight through the corona, as the coronal hole rotated
by the east solar limb.

(see, e.g., Miralles et al. 2001, Astrophys. J., 549, L257)