The WISDOM Radar: Unveiling the Subsurface Beneath the ExoMars Rover and Identifying the Best Locations for Drilling

The search for evidence of past or present life on Mars is the principal objective of the 2020 ESA-Roscosmos ExoMars Rover mission. If such evidence is to be found anywhere, it will most likely be in the subsurface, where organic molecules are shielded from the destructive effects of ionizing radiation and atmospheric oxidants. For this reason, the ExoMars Rover mission has been optimized to investigate the subsurface to identify, understand, and sample those locations where conditions for the preservation of evidence of past life are most likely to be found. The Water Ice Subsurface Deposit Observation on Mars (WISDOM) ground-penetrating radar has been designed to provide information about the nature of the shallow subsurface over depth ranging from 3 to 10 m (with a vertical resolution of up to 3 cm), depending on the dielectric properties of the regolith. This depth range is critical to understanding the geologic evolution stratigraphy and distribution and state of subsurface H2O, which provide important clues in the search for life and the identification of optimal drilling sites for investigation and sampling by the Rover's 2-m drill. WISDOM will help ensure the safety and success of drilling operations by identification of potential hazards that might interfere with retrieval of subsurface samples

3D Imaging of Buried Dielectric Targets with a Tomographic Microwave Approach Applied to GPR Synthetic Data

Effective diagnostics with ground penetrating radar (GPR) is strongly dependent on the amount and quality of available data as well as on the efficiency of the adopted imaging procedure. In this frame, the aim of the present work is to investigate the capability of a typical GPR system placed at a ground interface to derive three-dimensional (3D) information on the features of buried dielectric targets (location, dimension, and shape). The scatterers can have size comparable to the resolution limits and can be placed in the shallow subsurface in the antenna near field. Referring to canonical multimonostatic configurations, the forward scattering problem is analyzed first, obtaining a variety of synthetic GPR traces and radargrams by means of a customized implementation of an electromagnetic CAD tool. By employing these numerical data, a full 3D frequency-domain microwave tomographic approach, specifically designed for the inversion problem at hand, is applied to tackle the imaging process. The method is tested here by considering various scatterers, with different shapes and dielectric contrasts. The selected tomographic results illustrate the aptitude of the proposed approach to recover the fundamental features of the targets even with critical GPR settings

Modelling of GPR Wave Propagation and Scattering in Inhomogeneous Media

Numerical modelling of GPR wave propagation is becoming more and more important. The ability to build complex models to mirror complex subsurface structures can improve our understanding of how electromagnetic waves are effected by it. The main task of this thesis was to develop a model generator which simplifies complex model building by applying statistical processes. Both, the distribution of inhomogeneities and random rough surfaces can be described statistically. The developed model builder \emph{modelGPR} uses Gaussian distribution to create rough surfaces and to embed inhomogeneities into a host medium. The potentials of the software are presented by two examples. The first is related to ground truth measurements for SAR-satellites in polar regions and the second is devoted to water detection in the Martian shallow subsurface

GPR clutter amplitude processing to detect shallow geological targets

The analysis of clutter in A-scans produced by energy randomly scattered in some specific geological structures, provides information about changes in the shallow sedimentary geology. The A-scans are composed by the coherent energy received from reflections on electromagnetic discontinuities and the incoherent waves from the scattering in small heterogeneities. The reflected waves are attenuated as consequence of absorption, geometrical spreading and losses due to reflections and scattering. Therefore, the amplitude of those waves diminishes and at certain two-way travel times becomes on the same magnitude as the background noise in the radargram, mainly produced by the scattering. The amplitude of the mean background noise is higher when the dispersion of the energy increases. Then, the mean amplitude measured in a properly selected time window is a measurement of the amount of the scattered energy and, therefore, a measurement of the increase of scatterers in the ground. This paper presents a simple processing that allows determining the Mean Amplitude of Incoherent Energy (MAEI) for each A-scan, which is represented in front of the position of the trace. This procedure is tested in a field study, in a city built on a sedimentary basin. The basin is crossed by a large number of hidden subterranean streams and paleochannels. The sedimentary structures due to alluvial deposits produce an amount of the random backscattering of the energy that is measured in a time window. The results are compared along the entire radar line, allowing the location of streams and paleochannels. Numerical models were also used in order to compare the synthetic traces with the field radargrams and to test the proposed processing methodology. The results underscore the amount of the MAEI over the streams and also the existence of a surrounding zone where the amplitude is increasing from the average value to the maximum obtained over the structure. Simulations show that this zone does not correspond to any particular geological change but is consequence of the path of the antenna that receives the scattered energy before arriving to the alluvial depositsPeer ReviewedPostprint (published version

THE CHARACTERIZATION OF GROUND ICE DEPOSITS USING GROUND-PENETRATING RADAR TECHNIQUES

This study explores the capabilities of ground-penetrating radar (GPR) in the task of characterizing ground ice and the role this instrument can play in understanding the geomorphology of the cryosphere. The first article investigates the dielectric permittivity of ground ice using on-ice common-midpoint (CMP) GPR surveys conducted over massive stratified segregation ice, non-stratified segregation ice, and polygon ice wedges located on Ellesmere and Devon Islands, Nunavut. In comparison with ice cores, it was found that the dielectric permittivity of ground ice is most influenced by the volumetric ice content. This relationship appears to follow a modified complex refractive index (CRIM) dielectric mixing model. The second study applies the Brewster angle of incidence method to determine the dielectric permittivity of ground ice using endfire CMP surveys conducted atop the active layer. This method was able to predict dielectric permittivities within one dielectric unit of those established in the first article

In-Situ Radar Observation of Shallow Lunar Regolith at the Chang’E-5 Landing Site : Research Progress and Perspectives

Funding Information: This work is supported by the National Natural Science Foundation of China (Grant No. 42241139 and 42004099), the Opening Fund of the Key Laboratory of Lunar and Deep Space Exploration, Chinese Academy of Sciences (No. LDSE202005), the National Innovation and Entrepreneurship Training Program for College Students (No. 202310590016), the Fund of Shanghai Institute of Aerospace System Engineering (No. PZ_YY_SYF_JY200275), and the Shenzhen Municipal Government Investment Project (No. 2106_440300_04_03_901272).Peer reviewedPublisher PD

The influence of environmental conditions on volcanic processes on the terrestrial planets

This thesis aims to identify what environmental conditions are most influential on volcanic processes on the terrestrial planets. The research primarily focuses on intermediate-sized volcanoes on Venus and Mars; complete surveys of these planets have been performed in order to compile a new catalogue of all such features that lists morphological and locational information for each one. This has yielded three key findings: evolutionary precursors of large volcanoes and several morphologies of steep-sided domes have been identified on Venus, and low-relief shields with very similar morphologies have been identified on Venus and Mars. In each case, morphological differences and similarities are interpreted with respect to the changing configuration of magma within the edifices, differences in surface environment, and magma properties and supply rate. The research topic is also approached from two other aspects. Data obtained by the MARSIS radar sounder have been scrutinized in order to identify aquifers in the shallow Martian crust, and from this gauge the potential for crustal water to have influenced past volcanic activity. However, MARSIS has not succeeded in resolving Martian aquifers, leading to an independent estimate of its aquifer detection depth, and the conclusion that this instrument is insufficient to significantly constrain estimates of the crustal water budget. In addition, ground-penetrating radar surveys have been performed on Icelandic rootless cones, a category of small volcanic feature, in order to determine how their environments have affected their morphologies and interior structures during formation and subsequent modification. Five Icelandic cones have been surveyed, and three classes of cone morphology have been identified. Analogous cone morphologies are observed on Mars, and have been correlated to their interpreted modification environments using the results of the Icelandic surveys as a basis

Subsurface Mapping of Deserts and Polar Regions Using Radar Data on Earth and Mars

There are abundant resources buried underground that are difficult to be investigated remotely. This thesis is concerned with the development and utility of various novel processing methods for different radar instruments in the field of subsurface mapping on Earth and Mars. Firstly, advanced Synthetic Aperture Radar (SAR) imaging and Interferometric SAR (InSAR) techniques are applied to assess their potential for revealing subsurface features in the eastern Sahara Desert. The radar penetration depth at L-band (1.25 GHz) is estimated to be 1-2 m over paleochannels in the Sahara Desert, given an initial assumption that radar penetration occurs in the sand accumulation areas. The L-band frequency of previous and existing spaceborne SAR mission is shown to limit the penetration depth to a few metres below the surface. However, over the terrestrial ice-sheets, a radar instrument, the Multi-Coherent Radar Depth Sounder (MCoRDS) from the NASA Operation Ice Bridge (OIB) mission, can penetrate the ice sheet down to 3 km, revealing extensive englacial layers. An automated layer tracing method based on the Continuous Wavelet Transform (CWT) and Hough Transform (HT) is proposed to detect and digitise these englacial layers in Greenland. The results show that this proposed method can restore at least 72% of the isochrones when compared with previous results. Given the research interests of the department and inspired by the similarity of the layering phenomenon between the Earth and Martian polar regions, the layer tracing method is adjusted and applied to SHAllow RADar (SHARAD) radargrams from the Mars Reconnaissance Orbiter. This method is demonstrated on the SHARAD data in Promethei Lingula as this 6 is the only region with coherent subsurface echo returns near the south pole, resulting in the extraction of six distinct subsurface interfaces, which record past depositional and erosional history and may be associated with past climate change on Mars