Enhancing SHARAD Subsurface Imaging on Mars through a combination of Very-Large Roll (VLR) Maneuvers and Super-Resolution Techniques.

Introduction: To accommodate all the payloads onboard MRO and mitigate electromagnetic interferences with the other spacecraft payloads, the SHARAD’s antenna was installed on the zenith deck of the spacecraft bus — on the opposite side of MRO relative to the Martian surface. This configuration causes the SHARAD antenna to be affected by the conductive structure of the solar arrays, leading to a reduction of the signal strength received at the nadir [1]. Modest roll maneuvers (up to 28°) have regularly been executed to compensate for the sub-optimal antenna placement thereby enhancing the signal-to-noise ratio (SNR) of SHARAD surface returns by several decibels [2].

SHARAD Very-Large Rolls Observations: Recent EM simulations of the spacecraft effects on the antenna pattern [3] reveal larger roll angles up to 120°, which could yield SNR improvements of up to 10 dB. Following these findings, the MRO Project and SHARAD team planned a series of very-large-roll (VLR) maneuvers during eclipse periods to minimize ionospheric interference while managing energy and instrument constraints. The first test in May 2023, targeting the sedimentary deposits of Eumenides Dorsum in Medusae Fossae (ID 7858301), confirmed the modeling predictions. The radargram revealed significant improvements in SNR and penetration capabilities compared to standard roll observations (0° or 28°). The VLR technique facilitated a clearer identification of the basal interface at ~800 m depth, where sedimentary deposits typically exhibited high radar transparency (i.e., low-loss tangent). Additional tests were performed at the polar deposits and mid-latitude targets including ground ice, sediments, and volcanics in Arcadia, Amazonis, and Elysium Planitiae.

Super-Resolution Techniques Applied to VLR Observations: To further maximize the scientific value of VLR observations, we applied advanced signal processing algorithms properly designed to enhance the range resolution of sounder data [4,5]. Comparative analyses of radargrams acquired at 0° and 120° roll angles highlight the remarkable improvement in signal clarity and depth achieved when VLR maneuvers are combined with super-resolution techniques. At this conference, we will present quantitative assessments of SNR gains of VLR products versus standard products, demonstrating the superior performance of super-resolution algorithms when applied to VLR data. All these efforts aim to enhance radargram product quality and to refine the understanding of sedimentary and glacial terrains on Mars, which are of high scientific interest to the SHARAD community. While opportunities for VLR observations remain limited due to the operational complexity of these large maneuvers, planned observations over mid-latitude and polar terrains will offer further opportunities to exploit advanced signal processing algorithms [6,7] and improve clutter discrimination [8].

Acknowledgments: This work was supported by ASI contract 2023-9-HH.0 – CUP: F83C23000120005.

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