Analysis of Martian north polar ice cap layering with SHARAD data.

Martian polar ice caps are characterized by layered deposits, mainly composed ofwater ice and a small percentage of dust sediments. Past investigations found thatthe layering periodicities can be connected with variations of Mars orbital parameters, because of the orbital forcing phenomenon (Becerra, Sori, and Byrne2017).The periodicities quantification has already been made with the study of threedifferent types of stratigraphic observations: layer protrusion, local slope and layerbrightness versus depth (Becerra, Sori, and Byrne2017). This investigation is possible only where the layering emerges at the surface and where high resolutionDTMs are available. In order to extend this type of study inside the whole cap, inthis work we use SHARAD (Mars Reconnaissance Orbiter, NASA) radar data. Thestratification inside the cap is indeed well visible in the radargrams, thanks to thecontrast of dielectric constants of the different layers.We decided to isolate the subsurface regions of the North Polar Layered Deposits(NPLD) where the stratification is more evident and the signal is more intense,namely the ones that are nearest to the polar surface. Once isolated, we studiedtheir layering periodicities.With this purpose, we developed a semi-automated method to elaborate the radarsections. We use the Labeling of Connected Component technique, applied to radarimages, segmented through thresholding. Once isolated, we obtained the strataperiodicities inside these regions, through Time Series Analysis, and we comparedthem to the orbital parameters periodicities provided by Laskar, Correia, et al.2004simulations.From the analysis of our data, we found three main strata periodicities of approximately 70, 41 and 29m, that are partly consistent with the two values found fromthe superficial outcrops (Becerra, Sori, and Byrne2017). Most importantly, our1°and 3° periodicities appear to be in agreement with the obliquity and precessionvariations, suggesting that a possible link with the orbital forcing phenomenon canbe detected.