Full Vector Velocity Reconstruction Using Solar Orbiter Doppler Map Observations.

The Solar Orbiter mission opens up opportunities forthe combined analysis of measurements obtained by solar imagers and spectrometers. For the first time, different space spectrometerswill be located at wide angles to each other, allowing three-dimensional (3D) spectroscopy of the solar atmosphere.The aim of this work is to prepare the methodology to facilitate the reconstruction of 3D vector velocities from two stereoscopicLOS Doppler velocity measurements using the Spectral Imaging of the Coronal Environment (SPICE) on board the Solar Orbiter andthe near-Earth spectrometers, while widely separated in space. We develop the methodology using the libraries designed earlier for the STEREO mission but applied to spectroscopicdata from the Hinode mission and the Solar Dynamics Observatory. We use well-known methods of static and dynamic solar rotationstereoscopy and the methods of EUV stereoscopic triangulation for optically-thin coronal EUV plasma emissions. We develop new algorithms using analytical geometry in space to determine the 3D velocity in coronal loops. We demonstrate our approach with the reconstruction of 3D velocity vectors in plasma flows along "open" and "closed"magnetic loops. This technique will be applied first to an actual situation of two spacecraft at different separations with spectrometers onboard (SPICE versus the Interface Region Imaging Spectrograph (IRIS) and Hinode imaging spectrometer) during the Solar Orbiternominal phase. We summarise how these observations can be coordinated.