Automatic mapping and spatial analysis of high spatial resolution closed terrain depressions and mounds on martian landscapes

Abstract

The purpose of this paper is to illustrate a methodology for the automatic mapping and spatial analysis of high spatial resolution (metric scale) closed depressions and mounds on Mars landscapes. The proposed automatic procedure requires only a digital elevation model, a sink-filling algorithm and a basic map algebra operation all of which are available in the most commonly used Geographical Information Systems. Six high spatial resolution (1 m to 2 m) digital elevation models obtained from images of the High-Resolution Imaging Science Experiment (HiRISE) were selected as representatives of various Martian landscapes representing hypothesized aeolian, volcanic, hydrated, cratered, reticulate and sublimated terrains. This is not an exhaustive list of landscapes but it is representative of the variety of Martian landscapes. Metric spatial-scale closed depressions and mounds are commonly distributed in all the landscapes selected for this study and closed terrain depressions cover, on average, 25% of the Martian surface. Most closed depressions are small and shallow and have a complex shape. The area covered by mounds is more variable and is up to 36% in reticulate terrain and 43% in volcanic terrain. Again, most mounds are small, low and have complex shapes. For sublimated terrains the percentage covered by depressions, in the form of radiating araneiform channels, is equal to the percentage of mounds (material accumulated between the channels). Size distribution analysis reveals the fractal character of both closed depressions and mounds with the emergence of two main groups of landscapes. One group characterizes a detached geomorphology (aeolian and sublimated terrains), and the other group characterizes a connected geomorphology (volcanic, impact craters and reticulate terrain). The hydrated terrain is intermediate between the two main groups perhaps because of its plastic rheology. The proposed methodology is completely general and can be applied to any digital elevation model. The mapping and morphometric analysis of closed terrain depressions and mounds can assist planetary geologists in the mapping and interpretation of geological and geomorphological units and in the inference of geological processes.