The SUNRISE UV spectropolarimeter and imager for SUNRISE III

Sunrise is a balloon-borne solar observatory dedicated to the investigation of key processes of the magnetic field and the plasma flows in the lower solar atmosphere. The observatory operates in the stratosphere at an altitude of around 37 km in order to avoid image degradation due to turbulence in the Earth's atmosphere and to access the UV range. The third science flight of Sunrise will carry new instrumentation which samples the solar spectrum over a broad wavelength domain from the UV to the near IR and covers an extended height range in the solar atmosphere. A key feature of the Sunrise UV Spectropolarimeter and Imager (SUSI) operating between 309 nm and 417 nm, is its capability to simultaneously record a large number of spectral lines. By combining the spectral and polarization information of many individual lines with different formation heights and sensitivities, the accuracy and the height resolution of the inferred atmospheric parameters can be significantly increased. The spectral bands of SUSI are selected one at a time by rotating a diffraction grating with respect to a fixed polarimetry unit. The spatial and spectral field of view on the 2k x 2k cameras is 59” and 2.0 - 2.3 nm, respectively. A further innovation is the numerical restoration of the spectrograph scans by means of synchronized 2D context imaging, a technique that has recently produced impressive results at ground-based solar observatories.