One of the instruments onboard Sunrise III is the Sunrise UV Spectropolarimeter and Imager (SUSI), which covers the wavelength range from 309 nm to 417 nm, thus extending the observational capabilities of Sunrise III into the NUV. The spectrum across most of SUSI’s wavelength range has largely remained underutilized in solar physics so far. It includes thousands of spectral lines among which are more than 100 chromospheric lines, covering a height range of more than 1300 km in the solar atmosphere, seamlessly from deep photospheric to mid-upper chromospheric layers. Although the solar NUV intensity spectrum has been well observed, albeit at low spatial resolution, the polarized spectrum is poorly known.

from Feller et al. (2025)

The three SUSI cameras operate at a framerate of 47.040 fps in synchronization with the PMU. This implies that each modulation cycle (half PMU rotation lasting 256 ms) is sampled by 12 frames of the spectrograph cameras. During pre-flight tests, the synchronization error between cameras and PMU was measured to be below 0.36 ms, and the residual image motion due to PMU misalignment (beam wobbling) was below the required 0.1 pixels rms.
The SUSI spectrograph is equipped with two cameras in a dual-beam polarimetric configuration which allows suppressing measurement errors originating from residual jitter. The cameras, developed at MPS, meet the harsh environmental requirements of a stratospheric balloon flight and are based on UV optimized image sensors with very low noise (2 e− rms) to allow for efficient measurements in the deep, heavily photon-starved UV spectral lines. The data are recorded at a high frame rate of 47 frames per second (fps) to make them insensitive to residual large amplitude slow jitter of the system. All individual frames are stored on-board. This greatly enhances our flexibility in the later data reduction, in particular in terms of trading spatial and temporal resolution against signal-to-noise, depending on the actual science question.
High spatial resolution context images are obtained by re-imaging the 2D solar scene around the linear spectrograph entrance slit onto a separate camera. This setup is known as slit-jaw imaging. The slit-jaw imager, which is strictly synchronized to the two spectrograph cameras, detects residual jitter and optical wavefront errors. It allows for a post-facto numerical image restoration of the spectrograph scans following the technique developed by van Noort (2017) that has impressively stood the test in recent ground-based observations.

from Korpi-Lagg et al. (2025)