Estimation of Ice-Depth and Thickness Using Shallow Radar (SHARAD) in Phlegra Montes, Mars

Mars’s cryosphere contains an abundance of water ice at, near and under the surface. Radar and geomorphological studies to date have substantiated the existence of shallow ground ice and surface ice confirming the presence of debris covered glaciers, polygonal terrain, scalloped topography and other glacial-periglacial landforms on Mars. This research uses the Mars Reconnaissance Orbiter’s Shallow Radar (SHARAD) dataset with imagery from the Context Camera (CTX; 6 m/px) and High-Resolution Imaging Science Experiment (HiRISE; 25 cm/px) to measure the depth of subsurface ice at the study site, Phlegra Montes, Mars (30°N-52°N). Phlegra Montes is a 1400 km long massif region along a dichotomy boundary of Mars’ southern highlands and northern plains in the mid-latitudes. It has been proposed as a candidate human landing site on Mars and as a high-value target for cryospheric science and its potential for in-situ resources (ie. water ice). The goal of this study is to characterize and better understand Mars’ cryosphere in terms of the current water budget and recent evolutions in its subsurface water-ice content. Using 2D SHARAD power radargrams, clutter simulations and grid-maps of radar surface power return, ice consistency, and geomorphology derived from the Subsurface Water Ice Mapping (SWIM) team, 1543 SHARAD tracks intersecting the study region were analyzed and correlated using ArcMap 10.8, JMARS, SeisWare 10.1 and image editing software (Fig 1). In these analyses, ice-rich subsurface reflectors were identified in 72 radargrams with high confidence, 67 with medium confidence and 43 with low confidence. Two-way time delay radargrams were also converted to depth using the dielectric permittivity values in a two-layer model of free space (ɛ’=1.0) and water-ice (ɛ’=3.15), which is useful for detecting basal interfaces of ice-rich bodies such as lobate debris aprons (LDAs). As SHARAD data acquisition and coverage over Phlegra Montes continues to increase overtime, the total ice volume within the region is still difficult to calculate due to clutter (ie. low signal to noise ratio) from local topography. Moreover, instruments such as Polarimetric Synthetic Aperture Radar (PolSAR) and Ground Penetrating Radar (GPR) are necessary to map the distribution of ice within the first ten meters where ice is abundant on Mars but SHARAD is blind. This research will contribute to the future International Mars Ice Mapper (I-MIM) Mission in collaboration with the Italian Space Agency (ASI), Canadian Space Agency (CSA), Japan Aerospace Exploration Agency (JAXA) and National Aeronautics and Space Administration (NASA).