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

Constraining spatial pattern of early activity of comet 67P/C-G with 3D modeling of the MIRO observations