MERTIS: identifiability of spectral mineralogical features in dependence of the signal to noise ratio

Abstract

The ESA deep-space mission BepiColombo to planet Mercury will contain the advanced infrared remote sensing instrument MERTIS (MErcury Radiometer and Thermal infrared Imaging Spectrometer). The mission has the goal to explore the planets inner and surface structure and its environment. With MERTIS, investigations of Mercury's surface layer within a spectral range of 7 μm to 14μm shall be conducted to specify and map Mercury's mineralogical composition with a spatial resolution of 500 m. Due to the limited mass and power budget, the used micro-bolometer detector array will only have a temperature-stabilization and will not be cooled. The performance of the instrument is estimated by the theoretical description of the signal to noise ratio and the optics including the Offner spectrometer. The expected signal to noise ratio will be in the order of 100 and is mainly dependent on the surface temperature and the wavelength. The derived theoretical models are used to execute simulations to compute the passage of the infrared radiation of a hypothetical mineralogical surface composition and surface temperature through the optical system of MERTIS. The resulting noisy spectra are used to determine spectral features of the minerals. So it is possible to evaluate the conditions which are necessary to achieve the scientific goals of MERTIS. The intent is to estimate the spectral positions of mineralogical features like the Christiansen feature. This will be difficult because of the low signal to noise ratio and the low contrast of real mineral spectra.