Selecting the geology filter wavelengths for the ExoMars Panoramic Camera instrument

Claire R Cousins,Matthew Gunn,Bryan J Prosser,Dave P Barnes,Ian A Crawford,Andrew D Griffiths,Lottie E Davis,Andrew J Coates

doi:10.1016/j.pss.2012.07.009

Abstract

The Panoramic Camera (PanCam) instrument will provide surface remote sensing data for the ExoMars mission. A combination of wide-angle stereo, multispectral, and high resolution imagery will generate contextual geological information to help inform which scientific targets should be selected for drilling and analysis. One component of the PanCam dataset is narrowband multispectral imaging in the visible to near infrared, which utilises a dedicated set of 12 “geology” filters of predetermined wavelength and bandwidth to view the terrain, and provide information on composition and putative mineralogy. The centre wavelengths and bandwidths of these filters were optimised to account for the highly diverse mineralogical terrains the ExoMars rover will hopefully encounter. Six new alternative test filter sets were created, each optimised for the detection of either: sulfates, phyllosilicates, ferric oxides, mafic silicates, iron absorptions, and minor hydration absorptions. These six filter sets were cross-tested using database mineral reflectance spectra and Mars analogue rock multispectral data to find the best performing filter set. Once selected, the bandwidths of this filter set were also optimised. The filter set optimised to ferric oxide minerals was able to most accurately represent rock multispectral data, as well as capture subtle spectral features of hydrated minerals, including sulfates, phyllosilicates, and carbonates. These filters differ from those used on past missions (e.g., Pathfinder, Mars Exploration Rover) and represent the next evolutionary stage in PanCam instrument development. When compared to past filter sets, the updated ExoMars filters capture rock and mineral spectral data more effectively, enhancing the ability of the ExoMars PanCam to detect lithological and compositional variation within an outcrop.

Highlights

IntroductionThe ExoMars Panoramic Camera (MER) Pancam (e.g., Bell et al, 2004; Farrand et al, 2006, 2008; Johnson et al, 2007; Schmidt et al, 2009; Rice et al, 2010)
The correct identification of putative Martian palaeoenvironments using in situ Panoramic Camera (PanCam) data, including multispectral data, will be imperative to site selection and identification of drilling targets
Testing of the alternative filter sets on both mineral and rock spectral data has shown an improved performance of the new filter sets FERRIC, PHYL, and ALLFe, and of the earlier devised filter set F2-12

Summary

Introduction

The ExoMars Panoramic Camera (MER) Pancam (e.g., Bell et al, 2004; Farrand et al, 2006, 2008; Johnson et al, 2007; Schmidt et al, 2009; Rice et al, 2010). The PanCam for ExoMars will consist of 2 wide angle cameras (WACs) with a 341 field of view (FoV), separated by a distance of 50 cm; and a single High Resolution Camera with a narrow FoV of 41. The WACs each have a filter wheel to allow both narrowband multispectral imaging and broadband colour imaging. PanCam science for ExoMars will be achieved with a combination of wide-angle stereo colour panoramas and 3D digital elevation models (DEM), high resolution colour images/mosaics, reflectance spectra of Regions of Interest (ROI) and 2D mapping of spectral features (e.g., band depth)

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Conclusion