3D imaging of Mars' polar ice caps using orbital radar data

Abstract

Since its arrival in early 2006, various instruments aboard NASA's Mars Reconnaissance Orbiter (MRO) have been collecting a variety of scientific and engineering data from orbit around Mars. Among these is the SHAllow RADar (SHARAD) instrument, supplied by Agenzia Spaziale Italiana (ASI) and designed for subsurface sounding in the 15-25 MHz frequency band. As of this writing, MRO has completed over 46,000 nearly polar orbits of Mars, 30% of which have included active SHARAD data collection. By 2009, a sufficient density of SHARAD coverage had been obtained over the polar regions to support 3-D processing and analysis of the data. Using tools and techniques commonly employed in terrestrial seismic data processing, we have processed subsets of the resulting collection of SHARAD observations covering the north and south polar regions as SHARAD 3-D volumes, imaging the interiors of the north and south polar ice caps known, respectively, as Planum Boreum and Planum Australe. After overcoming a series of challenges revealed during the 3-D processing and analysis, a completed Planum Boreum 3-D volume is currently being used for scientific research. Lessons learned in the northern work fed forward into our 3-D processing and analysis of the Planum Australe 3-D volume, currently under way. We discuss our experiences with these projects and present results and scientific insights stemming from these efforts.

A Migration Model for the Polar Spiral Troughs of Mars

“…The TMPs are bounding surfaces within the NPLD that map the preexisting trough surfaces. For both of our modeled troughs, we map their TMPs (Figure ) in the 3‐D SHARAD volume (Foss et al, ) using the depth‐corrected data set which converts radar delay times to depths by assuming the real component of the dielectric constant is that of pure ice (ε′ ~ 3.15), consistent with bulk measurements of the NPLD (e.g., Grima et al, ). We take an approximately trough‐perpendicular transect of the TMP from a point currently on the surface to a point of initiation in the subsurface.…”

Automated reconstruction of subsurface interfaces in Promethei Lingula near the Martian south pole by using SHARAD data

“…Foss et al (2017) found the radargrams are misaligned with each other due to residual, along-track-variable delays introduced by the Martian ionosphere. Therefore, there may be a resultant slight offset between the surfaces of the radargram and cluttergram even when there are no occurrences of clutter reflections.…”

“…There is a dense data coverage in the polar regions due to the polar orbit. Extraction and analysis of subsurface layers from these data has recently expanded from traditional manual investigations to the use of 3-D imaged volumes (Foss et al, 2017). These semi-automated or automated, 2-D or 3-D methods allow the extraction of relevant information from these data in a more and more rapid and effective manner, thus facilitating the study of subsurface features in relation with the geological and climate history.…”

“…Furthermore, considering the SHARAD radargrams only show a 2-D profile of the probed region, it is necessary to combine radargrams from multiple orbits to reconstruct a 3-D subsurface structure. Foss et al (2017) first demonstrated the retrieval of 3-D volumes for both polar regions of Mars. Their 3-D volume imaging is built from 2-D interpolated images at every time delay position.…”

The Holy Grail: A road map for unlocking the climate record stored within Mars’ polar layered deposits

“…When radar data coverage is dense enough, various radar units can be mapped throughout the whole PLD, resulting in thickness measurements of prominent units and, in essence, a radar-based stratigraphy (Putzig et al, 2009;Smith and Holt, 2015;Nerozzi and Holt 2017). Additionally, a three-dimensional radar volume has been developed for observing in geometries not permitted with only two-dimensional, orbit parallel profiles (Foss et al, 2017;Putzig et al, 2018).…”