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Definition of an imaging spectrometer meeting the needs of UV solar physics

The study of the outer solar atmosphere requires combining imaging and spectroscopy in the UV lines formed in the high chromosphere, the transition region and the corona. We start from the science requirements and we define the instrumental specifications in terms of field-of-view (FOV), spatial, temporal and spectral resolution and bandpass. We propose two different all-reflection optical architectures based on interferometric techniques: Spatial Heterodyne Spectroscopy (SHS); and Imaging Transform Spectrometer (IFTS). We describe the different set-ups and compare the potential performances of the two types of solutions, and discuss their feasibility. We conclude that IFTS appears to be the best solution, meeting the needs of UV solar physics. However, we point out the many difficulties to be encountered, especially as far as metrology is concerned.