Defining Surface Types of Mars using Global CRISM Summary Product Maps

For many regions on Mars, the surface composition and its geological history have been debated in the literature. Because of the limited surface coverage of in situ measurements, either new data or new processing methodologies are required to get a better understanding of the Martian geology. This paper presents the results of a multivariate, unsupervised, analysis on underutilized CRISM (Compact Reconnaissance Imaging Spectrometer) multispectral mapping mode data set for surface type analysis. The devised summary products of Pelkey et al. (2007) and Viviano-Beck et al. (2014) are averaged for the CRISM similar to 5 degrees x 5 degrees mosaic grids and used to analyze the variability in this data set. The averaged summary product values are studied using correlation coefficients calculated between summary products, as well as the correlation with dust coverage and elevation. The degree of correlation is used to interpret the summary products for the global distribution of mafic and secondary minerals and the effect of external factors such as ice, atmosphere, and dust coverage. With unsupervised clustering, all grid pixels are classified based on the spectral variability. These clusters are plotted as global maps and interpreted for geological variations in the CRISM data. Some clusters spatially correspond with previously recognized compositional distinct regions Northern Lowlands, Southern Highlands, Meridiani Planum, Syrtis Major, and Nili Fossae. Several other clusters are described here for the first time such as Solis Planum, Ophir Planum, and Hellas Basin. These regions cover known geological units, but the interpretation of the spectral variability is uncertain whether it relates to geological or external factors.