DeSIRer: a new, fast and flexible non local thermodynamic equilibrium inversion code

The solar surface is permeated by magnetic fields. In the photosphere, they can be measured with reasonable precision using spectral lines well described in local thermodynamic conditions (LTE) and analysed using well-known and fast inversion codes. In the chromosphere, however, the situation is more complex. In the one hand, the magnetic fields are weaker and associated with more dynamic plasmas than in the photosphere. This calls for faster measurements and better polarimetric precisions. On the other hand, the target spectral lines suffer from non-LTE effects, what hinders their analisys and interpretation. Presently, there exist inversion codes able to deal with non-LTE spectral lines (e.g., Nicole, Hazel, Stic, or Snapi). Here, I present DeSIRer (Departure Coeficients Inversor Code): a software able to simultaneously invert photospheric and chromospheric spectral lines form under both, LTE and non-LTE conditions. The code is being developed under the framework of the upcoming third flight of the SUNRISE balloon-borne solar mission. The instrument suite of SUNRISE will provide unprecedented co-spatial and co-temporal polarimetric observations in different spectral lines located in the near ultraviolet, visible, and near infrared spectral ranges and covering both, the photosphere and the chromosphere. Desire is tailored in such a way that it is very fast, easily parallelizable, and user friendly. It is based on the well known SIR (Stokes Inversion based on Response Functions; Ruiz Cobo & del Toro Iniesta 1992) and RH (Uitenbroek 2001) codes. Moreover, it uses (if chosen) a model initialization based on convolutional neural networks, which speeds up the inversion process significantly. Basic operation and several examples using synthetic and real observations will be presented.