Simulating Enfys: End-to-End Surface Reflectance Spectroscopy Simulations of the Infrared Spectrometer for the ExoMars Rosalind Franklin Rover

The Enfys infrared spectrometer for the ExoMars Rosalind Franklin rover mission will perform high-resolution (Δ𝜆/𝜆 > 100) reflectance spectroscopy over 0.9 – 2.5 μm to constrain the surface mineralogy and geological context of the rover landing site, traverse, and subsurface investigations [1, 2]. Enfys has a novel dual-photodiode and scanning linear-variable filter design. We present a component level model of Enfys, describing the spectroradiometric and thermal response of the photodiodes and optics. This model, or instrument transfer function, describes the conversion of scene radiance to noisy arbitrary digital numbers, accounting for component dependencies on thermal conditions across the nominal mission lifetime. We have implemented the model into an end-to-end software simulation, capable of physically modelling mission observation scenarios, to produce predictions of spectral signature signal-to-noise ratio across the environment and instrument observation parameter spaces.

Here we present results validating the model against Enfys calibration measurements, and illustrate the breadth of simulations that can be accomplished through the instrument and environment coupled simulation. We show results between sunrise and sunset at Oxia Planum for a variety of Solar Longitudes, for a variety of surface orientations relative to the rover pointing and mast height of 2 m. We’ve modelled the reflectance of materials representative of the iron oxides, mafic and clay mineralogy we can expect to encounter as well as calibration standards, by deriving single scattering albedos from laboratory measurements and Hapke modelling the bidirectional reflectance distribution functions [3]. We report results of expected photo-generated current and signal-to-noise ratios for these varying observation scenarios across the Enfys spectral range and operational thermal range, and discuss implications on the sensitivity limits of Enfys for spectral and photometric classification tasks.

[1] Vago, J. L et al, 2017, Astrobiology, 17(6-7), 471–510; [2] Grindrod, P. M. et al, 2025. EPSC-DPS2025-154; [3] Hapke, B., 2012. Theory of Reflectance and Emittance Spectroscopy, Cambridge University Press