GRAIN-SIZE ANALYSIS AT GALE CRATER, MARS: TESTING THE APPLICABILITY OF AUTOMATIC GRAIN DETECTION SOFTWARE

On Earth, grain-size analysis is able to provide quantitative morphological characteristics of sedimentary particles that can be used to reconstruct the transport and depositional history of sediments. In order to overcome some of the difficulties and limitations encountered when applying the same techniques to Mars, we here report on the application of an automatic method. We have developed best practice techniques for using the automatic object detection software BASEGRAIN [Detert & Weitbrecht, 2012] with images taken on the surface of Mars by the MARDI camera on the Curiosity rover. MARDI images were chosen for this preliminary study because of the fixed surface scale, but given suitable scale information, this technique could be applied to different Curiosity camera images to expand the capability of the mission. We first tested and calibrated the software via comparison with previous results with manual methods [e.g. Yingst et al., 2013], producing similar results albeit with a factor of 2-3 increase in the number of analysed grains. We then applied the automated method to two separate sections of the traverse made by Curiosity, using Planetary Data System (PDS) MARDI images that met our criteria for use with BASEGRAIN: Sol 0 to 318 (8 images), and Sol 328 to 566 (83 images). To quantify grain size, we determined D50 and D84 values from calculated cumulative frequency plots for grain sizes between 3 and 64 mm, for correlation with surface features and units. This method correctly identifies the effect of the Sky Crane landing method on the grain size of surface clasts, and also suggests a correlation with geological units.

References

Detert, M., V. Weitbrecht (2012), Automatic object detection to analyze the geometry of gravel grains – a free stand-alone tool. River Flow 2012, R.M. Muños (Ed.), Taylor & Francis Group, London, ISBN 978-0-415-62129-8, pp. 595-600.

Yingst, R.A. et al. (2013), Characteristics of pebble- and cobble-sized clasts along the Curiosity rover traverse from Bradbury Landing to Rocknest, J. Geophys. Res., 118, 2361–2380.