Endmember spectra and classified maps derived from CRISM targeted data at the south pole of Mars

Overview

Current maps of compositional variation across south polar ice exposures on Mars do not resolve the meter-scales at which erosional processes are most active, ultimately limiting our understanding of how the deposits form and evolve and how they can be used to interpret long-term climate records. In this study, we use k-means clustering and random forest classification to identify and map a set of universal spectral endmembers across 167 high-resolution observations acquired during southern summer by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM). The 21 endmembers show distinct combinations and strengths of key infrared absorption features reflecting diverse mixtures of CO₂ ice, H₂O ice, and dust. The resulting compositional framework can be used to characterize the nature of both seasonal CO₂ frost and the residual ices it overlies across a variety of terrains. 

Contents

The repository contains three .zip files, which can be expanded to access the files described below:

• classified_maps.zip
  • lookup_files
    • SP_CRISM_RF_ColorMap.clr : An ESRI-formatted color map file that can be used to apply the endmember color scheme to random forest-classified maps in ArcGIS (see Symbology settings).
    • SP_CRISM_RF_ColorMap.txt : A text file that can be loaded into Python as a numpy array and used to generate a matplotlib color ramp. Row indices correspond to endmember numbers (see below) and columns are red, green, and blue values scaled from 0 to 1.
    • SP_CRISM_RF_Endmember_Lookup.csv : A lookup table that can be used to cross-reference between endmember numbers (as stored in GeoTiffs or the indices of the colormaps above) and corresponding endmember names (C1, Dc2, etc.).
  • morphologic_reference
    • Contains GeoTiffs of the R1330 spectral parameter (reflectance at 1330 nm) for each processed CRISM observation. Filenames indicate the observation ID, Mars Year, and solar longitude (Ls) of acquisition ("Ls314-07" = Ls 314.07º). These images can be used as a reference for the surface morphology and albedo of each scene. Tie points used to georeference these images to other datasets can be applied to the random forest classification maps to properly align endmember mapping results.
  • random_forest_classification
    • Contains GeoTiffs of the random forest classification results for each processed CRISM observation. Filenames indicate the observation ID, Mars Year, and solar longitude (Ls) of acquisition ("Ls314-07" = Ls 314.07º). These images are not rendered to display colors consistent with the publication figures, but instead store the endmember classification for each pixel as a number from 0 to 21; use the contents of lookup_files to find the corresponding endmember name or render the image with the color scheme from the publication. To view rendered summary plots of each observation, see the contents of observation_info. To georeference these images to other datasets, use the corresponding morphologic reference (see above) to set tie points.
• observation_info.zip
  • footprint_shapefile
    • Contains the components of an ESRI shapefile that outlines the surface footprint/coverage of each processed CRISM observation. The attributes associated with each observation are the same as those in observation_lookup below. Note that the polygons extend slightly beyond the area shown in maps in random_forest_classification due to the inclusion of border pixels.
  • observation_lookup
    • SP_CRISM_Classified_Obs_Info.csv : Information on each processed CRISM observation; this is the same file as Table S1 in the publication. Includes the MY and Ls of acquisition and (where applicable) the figure panel where the observation appears in the publication. The location of each observation is indicated with Center Latitude/Longitude and the assigned Spatial Domain (see Figure 1 in the publication). The Observation ID can be used to locate the source Targeted Reduced Data Record (TRDRs, Version 3) on the Geosciences Node of the Planetary Data System. The spatial extent of each observation is provided in the footprint_shapefile described above. 
  • summary_plots
    • Contains summary plots of the endmember map generated for each processed CRISM observation. Each plot notes the observation ID, Mars Year, and Ls and displays the morphologic reference map, random forest classification map, and a breakdown of the endmembers that are present. To access the maps rendered here, see the contents of classified_maps.zip.
    • Also contains the full-resolution version of Figure S3 from the publication (All_Obs_Unprojected.png), which can be used to lookup observations of interest via small labels above each map. 
• spectral_library.zip
  • Contains spectral libraries with the median spectrum of each endmember as presented in Figure 3 in the publication. A basic text file listing the wavelength (WVL) and normalized reflectance values for each endmember is included (SP_CRISM_EndmemberMedians.txt) as well as an ENVI-formatted spectral library (SP_CRISM_EndmemberMedians_ENVI.sli). Note that a subset of the 438 wavelengths sampled in the source CRISM data were removed around the longest and shortest wavelengths and the filter boundary to avoid error-prone bands, leaving these spectral libraries with 404 bands.