  Our aim is to investigate early activity (July 2014) of 67P/CG with 3D coma
and radiative transfer modeling of MIRO measurements, accounting for nucleus
shape, illumination, and orientation of the comet. We investigate MIRO line
shape information for spatial distribution of water activity on the nucleus
during the onset of activity. During this period we show that MIRO line shape
have enough information to clearly isolate contribution from Hapi and Inhotep
independently, and compare it to the nominal case of activity from the entire
illuminated surface. We also demonstrate that spectral line shapes differ from
the 1D model for different viewing geometries and coma conditions relevant to
this study. Specifically, line shapes are somewhat sensitive to the location of
the terminator in the coma. At last, fitting the MIRO observations we show that
the Imhotep region (possible extended source of H$_{2}$O due to CO$_{2}$
activity) contributes only a small fraction of the total number of water
molecules into MIRO beam in the early activity. On the other hand, a strong
enhancement of water activity from the Hapi region seems required to fit the
MIRO line shapes. This is consistent with earlier Rosetta results.
Nevertheless, within the assumption of our coma and surface boundary
conditions, we cannot get a reasonable fit to all MIRO mapping observations in
July 2014, which may illustrate that a more sophisticated coma model or more
accurate temperature/velocity distribution is needed.
