  We perform calorimetry on the bright gamma ray burst (GRB) 030329 by fitting
simultaneously the broadband radio afterglow and the observed afterglow image
size to a semi-analytic magnetohydrodynamical (MHD) and afterglow emission
model. Our semi-analytic method is valid in both the relativistic and
non-relativistic regimes, and incorporates a model of the interstellar
scintillation that substantially effects the broadband afterglow below 10 GHz.
The model is fitted to archival measurements of the afterglow flux from 1 day
to 8.3 years after the burst. Values for the initial burst parameters are
determined and the nature of the circumburst medium is explored. Additionally,
direct measurements of the lateral expansion rate of the radio afterglow image
size allow us to estimate the initial Lorentz factor of the jet.

High Energy Astrophysical Phenomena