Continuous Particle Size Mapping of Alluvial Fan Material in Mojave Crater from HiRISE Imagery

In terrestrial environments, the need to understand sediment size distributions across entire watersheds has led to the development of remote sensing methods that allow grain sizes to be automatically measured and continuously mapped from imagery. These methods use local image texture values empirically calibrated with field data or, alternatively, with direct on-screen measurements of visible particles. Crucially, some of these methods are designed to operate in patches where particles can be as small as 0.5 image pixels. This new approach to grain size measurement therefore opens up the possibility of using HiRISE imagery in order to measure and map coarse material grain sizes on the Martian surface. In this paper, we successfully transfer methods developed for terrestrial environments to HiRISE imagery in order to produce continuous maps of coarse sediment sizes in the range of 128mm to 4000mm for alluvial fan material in Mojave crater, Xanthe terra, Mars. Figure 1 shows some typical results with grain size data overlain onto the original HiRISE imagery. Grain size data is presented in logarithmic phi units which are commonly used in terrestrial sedimentology. Figure 1 demonstrates that this method can quantitatively categorize a range of sediment types from cobbles to boulders. Such an approach therefore has the potential to make an important contribution to the understanding of Martian sedimentology and to the selection of future landing sites. Figure 1. Example of particle size mapping applied to alluvial fan material in Mojave crater, Xanthe Terra,Mars.