Correlating multispectral imaging and compositional data from the Mars Exploration Rovers and implications for Mars Science Laboratory Ryan B. Anderson a,b,⇑ , James F. Bell III c a United States Geological Survey Astrogeology Science Center, 2255 N. Gemini Drive, Flagstaff, AZ 86001, USA b Cornell University, Department of Astronomy, 406 Space Sciences Building, Ithaca, NY 14853, USA c Arizona State University, School of Earth and Space Exploration, Building INTDS-A, Room 115B, Box 871404, Tempe, AZ 85287, USA article info Article history: Received 5 March 2012 Revised 28 October 2012 Accepted 21 November 2012 Available online 5 December 2012 Keywords: Mars Image processing Spectroscopy Data reduction techniques abstract In an effort to infer compositional information about distant targets based on multispectral imaging data, we investigated methods of relating Mars Exploration Rover (MER) Pancam multispectral remote sensing observations to in situ alpha particle X-ray spectrometer (APXS)-derived elemental abundances and Mössbauer (MB)-derived abundances of Fe-bearing phases at the MER field sites in Gusev crater and Meridiani Planum. The majority of the partial correlation coefficients between these data sets were not statistically significant. Restricting the targets to those that were abraded by the rock abrasion tool (RAT) led to improved Pearson’s correlations, most notably between the red–blue ratio (673 nm/ 434 nm) and Fe 3+ -bearing phases, but partial correlations were not statistically significant. Partial Least Squares (PLS) calculations relating Pancam 11-color visible to near-IR (VNIR; 400–1000 nm) ‘‘spectra’’ to APXS and Mössbauer element or mineral abundances showed generally poor performance, although the presence of compositional outliers led to improved PLS results for data from Meridiani. When the Meridiani PLS model for pyroxene was tested by predicting the pyroxene content of Gusev targets, the results were poor, indicating that the PLS models for Meridiani are not applicable to data from other sites. Soft Independent Modeling of Class Analogy (SIMCA) classification of Gusev crater data showed mixed results. Of the 24 Gusev test regions of interest (ROIs) with known classes, 11 had >30% of the pixels in the ROI classified correctly, while others were mis-classified or unclassified. k-Means clustering of APXS and Mössbauer data was used to assign Meridiani targets to compositional classes. The cluster- ing-derived classes corresponded to meaningful geologic and/or color unit differences, and SIMCA classi- fication using these classes was somewhat successful, with >30% of pixels correctly classified in 9 of the 11 ROIs with known classes. This work shows that the relationship between SWIR multispectral imaging data and APXS- and Mössbauer-derived composition/mineralogy is often weak, a perhaps not entirely unexpected result given the different surface sampling depths of SWIR imaging (uppermost few microns) vs. APXS (tens of lm) and MB measurements (hundreds of lm). Results from the upcoming Mars Science Laboratory (MSL) rover’s ChemCam Laser Induced Breakdown Spectroscopy (LIBS) instrument may show a closer relationship to Mastcam SWIR multispectral observations, however, because the initial laser shots onto a target will analyze only the upper few micrometers of the surface. The clustering and classification methods used in this study can be applied to any data set to formalize the definition of classes and iden- tify targets that do not fit in previously defined classes. Published by Elsevier Inc. 1. Introduction Images of the surface of Mars and measurements of its elemen- tal composition provide valuable insight into the planet’s geologic history. Cameras have been included on every landed mission to Mars (e.g., Mutch et al., 1972; Evans and Adams, 1979; Smith et al., 1997; Bell et al., 2003; Lemmon et al., 2008), and these mis- sions have also been capable of in situ compositional (Clark et al., 1977; Rieder et al., 1997, 2003; Gellert et al., 2009) or mineralogic (Klingelhöfer et al., 2003a) analysis. While multispectral imaging can be used to survey the geologic and color properties of materials around a rover or lander, detailed compositional information is typically restricted to localized spots close to the spacecraft. Even in the case of the laser-induced breakdown spectroscopy (LIBS) instrument (ChemCam) on the upcoming Mars Science Laboratory 0019-1035/$ - see front matter Published by Elsevier Inc. http://dx.doi.org/10.1016/j.icarus.2012.11.029 ⇑ Corresponding author at: United States Geological Survey Astrogeology Science Center, 2255 N. Gemini Drive, Flagstaff, AZ 86001, USA. Fax: +1 (928) 556 7014. E-mail addresses: rbanderson@usgs.gov, randerson@astro.cornell.edu (R.B. An- derson), Jim.Bell@asu.edu (J.F. Bell III). Icarus 223 (2013) 157–180 Contents lists available at SciVerse ScienceDirect Icarus journal homepage: www.elsevier.com/locate/icarus