Semi-automated crater depth measurements

Impact cratering is a major process driving planetary landscape evolution. Statistics of craters spatial density is extensively used to date planetary surfaces. Their degradation state and morphometry are also key parameters to understand surface processes.

To exploit the increasing coverage of digital terrain models (DEM) on Mars at high spatial resolution, we propose a semi-automated pipeline for crater depth measurement based on coupled optical images and DEM. From a craters map shapefile coupled with a co-registered DEM, we propose to measure crater depth as the difference between the 60^th percentile of elevation values on the edge of the crater and the 3^rd percentile value of the elevations within the crater. We present here this method and its calibration.

•

Aside to this paper, we provide a simple python code of this pipeline.

•

This method can rapidly produce crater depth dataset big enough to be interpreted statistically.

•

We provide solid tests on the precision of measured crater depth. Especially, we show that minimal elevation value within a crater, sometime used as crater floor elevation, is a far less precise approximation than a low percentile of elevation.

The Fractal Nature of Planetary Landforms and Implications to Geologic Mapping

The primary product of planetary geologic and geomorphologic mapping is a group of lines and polygons that parameterize planetary surfaces and landforms. Many different research fields use those shapes to conduct their own analyses, and some of those analyses require measurement of the shape's perimeter or line length, sometimes relative to a surface area. There is a general lack of discussion in the relevant literature of the fact that perimeters of many planetary landforms are not easily parameterized by a simple aggregation of lines or even curves, but they instead display complexity across a large range of scale lengths; in fewer words, many planetary landforms are fractals. Because of their fractal nature, instead of morphometric properties converging on a single value, those properties will change based on the scale used to measure them. Therefore, derived properties can change-in some cases, by an order of magnitude or more-just when the measuring length scale is altered. This can result in significantly different interpretations of the features. Conversely, instead of a problem, analysis of the fractal properties of some landforms has led to diagnostic criteria that other remote sensing data cannot easily provide. This paper outlines the basic issue of the fractal nature of planetary landforms, gives case studies where the effects become important, and provides the recommendation that geologic mappers consider characterizing the fractal dimension of their mapped units via a relatively simple, straightforward calculation.

Morphology and composition of the surface of Mars: Mars Odyssey THEMIS results

The Thermal Emission Imaging System (THEMIS) on Mars Odyssey has produced infrared to visible wavelength images of the martian surface that show lithologically distinct layers with variable thickness, implying temporal changes in the processes or environments during or after their formation. Kilometer-scale exposures of bedrock are observed; elsewhere airfall dust completely mantles the surface over thousands of square kilometers. Mars has compositional variations at 100-meter scales, for example, an exposure of olivine-rich basalt in the walls of Ganges Chasma. Thermally distinct ejecta facies occur around some craters with variations associated with crater age. Polar observations have identified temporal patches of water frost in the north polar cap. No thermal signatures associated with endogenic heat sources have been identified.