QUANTIFICATION OF LAYERING PERIODICITIES WITHIN MARTIAN NORTH POLARICE CAP THROUGH TIME SERIES ANALYSIS OF SHARAD RADAR SIGNAL

Martian polar ice caps are characterized by layered deposits, mainly composed of water ice and a small percentage of dust sediments. Past investigations found that the layering periodicities can be connected with variations of Mars orbital parameters, because of the orbital forcing phenomenon (Becerra, Sori, and Byrne 2017).

The periodicities quantification has already been made with the study of three different types of stratigraphic profiles: layer protrusion, local slope and layer brightness versus depth (Becerra, Sori, and Byrne 2017). This investigation is possible only where the layering emerges at the surface and where high resolution DTMs are available. In order to extend this type of study inside the whole cap, in this work we use SHARAD (Mars Reconnaissance Orbiter, NASA) radar data. In fact, the stratification inside the cap is well visible in the radargrams, thanks to the contrast of dielectric constants of 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 studied their layering periodicities.

With this purpose, we developed a semi-automated method to elaborate the radar sections. We use the Labeling of Connected Component technique, applied to radar images, segmented through thresholding. Once isolated, we obtained the strata periodicities inside these regions, through Time Series Analysis, and we compared them to the orbital parameters periodicities provided by Laskar et al. 2004 simulations.

From a preliminary analysis of our data, we found two main strata periodicities of approximately 44 and 26 m, that are consistent with the values found from the superficial outcrops (Becerra, Sori, and Byrne 2017), demonstrating that these peiodicities are well recorded throughout the whole cap.

Decoding the information contained into these strata will help us to deepen the climatic evolution and the entity of the orbital forcing phenomenon on Mars.