Non-Uniqueness Of Atmospheric Modeling

                             Philip Judge
                      High Altitude Observatory,
               National Center for Atmospheric Research

I re-examine on the simple question: How can we use the emitted
photons to extract meaningful information on the (chromosphere,)
transition region and corona?  Using examples, I will conclude that
the only safe way to proceed is through forward models, especially
when the plasmas are unresolved. In this way, inherent non-uniqueness
is handled by adding information through explicit physical assumptions
and restrictions made in the modeling procedure. The alternative,
"inverse" approaches rely (often implicitly) on more subjective
choices that have little theoretical support.  Although focussed on
the transition region, there are implications for more general
problems concerning the use of photons to diagnose conditions
in astrophysical plasmas.