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

Performance validation of the ExoMars 2018 WISDOM GPR in ice caves, Austria

International audienceThe WISDOM (Water Ice Subsurface Deposits Observations on Mars) Ground Penetrating Radar has been selected to be part of the ExoMars 2018 exobiological rover mission. A prototype has been tested during the Mars Simulation organized by the Austrian Space Forum in Alpine ice caves in Dachstein, Austria. This campaign provided the opportunity to validate methods developed to process WISDOM’s data in a well-documented environment and to retrieve geometrical and quantitative information about the 3D structure and the electromagnetic properties of the subsurface. We estimate the ice thickness in different locations inside the ice caves, and show that this ice is formed of fine strata with different properties. Data analysis allows reconstructing the bedrock in a 3D environment where a complete survey was performed

Radar Subsurface Imaging by Phase Shift Migration Algorithm

In this paper the phase shift migration based Syn- thetic Aperture Radar (SAR) is described and applied on radar imaging for dual polarized ground penetrating radar system (GPR). Conventional techniques for SAR imaging focusing use the matched filter concept and convolve the measurement data with a filter impulse response (convolution kernel) which is modified by the range. In fact, conventional techniques for SAR imaging technique can be considered as ray-tracing based SAR imaging technique. It is an efficient technique to obtain focused radar images, when the medium is homogeneous so that the rays of EM wave propagation can be treated as straight lines. However, in case of layered materials the waves are refracted on the interface between two different materials. In contrast, phase shift migration based SAR imaging technique is through EM field extrapolation by phase shift to obtain the reflected EM intensity and radar imaging of scatterers' reflectivity in the radar illumination area. Although EM wave is refracted on the interface of different materials, the EM wave phase is unchanged. Compared to conventional SAR imaging technique, phase shift migration based SAR imaging approach is more suited to obtain focused radar subsurface imaging for GPR systems. In this paper the phase shift migration approach is applied to experimental data as well as practical measurement data. Meanwhile, a background removal algorithm and a spreading and exponential correcting technique is applied to improve the achievement. The presented focused subsurface and scatters radar imaging results show that phase shift migration based SAR technique is satisfied for radar subsurface imaging and inhomogeneous medium imaging

External calibration of GPR antenna accommodated on a rover

International audienceThis paper describes an external calibration of an antenna system that is used for rover based GPR-Systems. The used antenna system consists of two identical crossed double Vivaldi structures. After the description of the radar system, the electrical properties of the antenna system are characterized. The influence of the rover chassis is shown with the help of some simulated footprints. After explanation of the calibration in detail, it is applied to outdoor measurements

Advance of WISDOM GPR Antenna for ExoMars 2018 Mission

The Experiment "Water Ice and Subsurface Deposit Observations on Mars" (WISDOM) is a Ground Penetrating Radar (GPR) selected to be part of the Pasteur payload on board the rover of European Space Agency's (ESA) ExoMars 2018 mission. The GPR antenna system described in this paper is the consequent progression of former developments [1, 2] incorporating changed requirements and further optimizations. Main constraints are the mass, the temperature range as well as the ultra-wide band demand. The antenna requirements which are to fulfill for this very specific GPR application are described here. Furthermore, it is given an overview about the lightweight design and its realization. Simulated and measured antenna performance is compared in this paper

Framework for the Generation of Large Datasets of Synthetic RADAR Soundings of the Martian Subsurface

International audienceEssential for the successful training and application of AI tools to the automated processing of planetary RADAR soundings is the availability of sufficiently labeled and annotated data for the specific instruments and solar system bodies. For data of planetary RADAR sounders, no ground truth is typically available, resulting in labels and annotations derived from models of observations. A different approach is to generate synthetic data by simulation of the RADAR sounding process, including all relevant instrument characteristics and models of the surface and subsurface of the sounded solar system body. In this context, the aim of such automated processing approaches is to annotate subsurface signatures, e.g., hyperbolas, that could indicate point-like scatterers, which are of interest for a permittivity estimation. To simplify the generation of many RADAR datasets for the WISDOM instrument, a payload of the ExoMars Rosalind Franklin rover, scheduled for 2022, we have developed a framework to efficiently create random variations of models of Oxia Planums subsurface. Using this framework, we aim to generate sufficient data for the automatic processing of the WISDOM measurements and the extraction of subsurface features. Furthermore, the framework can be applied to other missions and RADAR sounders and extended to integrate synthetic results from other instruments. In this presentation, we demonstrate initial results generated with the framework, as well as introduce the general workflow and steps necessary to parametrize the model generation

Ultra light-weight antenna system for full polarimetric GPR applications

International audienceThe motivation to develop an ultra light-weight antenna system was driven by a space borne radar application. The experiment ldquowater ice and subsurface deposit observations on Marsrdquo (WISDOM) is a ground penetrating radar (GPR) selected to be part of the Pasteur payload on board the rover of the ExoMars mission. Among the Pasteur panoramic instruments on the ExoMars rover, only WISDOM can provide a view of the subsurface structure. WISDOM is the first GPR on a planetary rover. It has been designed to characterize the shallow subsurface structure of Mars. WISDOM will for the first time give access to the geological structure, electromagnetic nature, and, possibly, hydrological state of the shallow subsurface by retrieving the layering and properties of the buried reflectors. It will address important scientific questions regarding the planet's present state and past evolution. The measured data will also be used to determine the most promising locations to obtain underground samples with the drilling system mounted on board the rover. The instrument's objective is to get high-resolution measurements down to 2 m depth in the Martian crust. The radar is a gated step frequency system covering a frequency range from 500 MHz to 3 GHz. The radar is fully polarimetric and makes use of an ultra wideband antenna system based on Vivaldi antenna elements. The paper describes antenna requirements to fulfil for this very specific GPR application and it gives an overview about the light-weight design and its realization. Simulated and measured antenna performance is compared in this paper. Test measurements were performed in permafrost regions on earth

Full Polarimetric GPR Antenna System Aboard the ExoMars Rover

A full polarimetric antenna system on board the ExoMars rover is part of the Experiment "Water Ice and Subsurface Deposit Observations on Mars" (WISDOM). The WISDOM-Experiment is a Ground Penetrating Radar (GPR) selected to be part of the Pasteur payload aboard the rover of the ExoMars mission. The Pasteur Panoramic Instruments (wide angle camera PANCAM, infrared spectrometer MIMA and WISDOM) will perform large-scale scientific investigations at the sites the Rover will visit. Among these instruments, WISDOM is the only that can provide a view of the subsurface structure prior to drilling. WISDOM has been designed to characterize the shallow subsurface structure of Mars. WISDOM will for the first time give access to the geologic structure, electromagnetic nature, and, possibly, hydrological state of the shallow subsurface by retrieving the layering and properties of the buried reflector

Multiple Compressive Projection Measurement for Stepped Frequency Radar

In modern communication and measurement sys- tems, signal detection and estimation play a major role. Actually, the above two terms can be considered as one issue, e.g. pure detection by densely listing all possible diversites. The penalty is however the system complexity. Up to now, a lot of work have been invested, especially the recent compressed sensing (CS) technique [1], which is a subtle mathmatic application in practice and leads to a great sucess in signal detection both for communication and measurement, e.g. radar technique. In spite of this radical progress there are still a lot of open problems. One of them is the "noise" including background noise and non- ideal signal modelling, which is not just a problem for CS but a general difficulty for signal processing. Although there are many sophisticated recovery algorithms developed to cope with noise, the performance will be usually impacted by inaccurate noise estimation or modelling error. In this paper, we will analyti- cally describe the multiple compressive projection measurement (mCPM1 or MCPM) introduced in [2]. Both theoretical analysis and numerical evaluations show that mCPM is a promising measurement system

WISDOM Antenna Pattern in the presence of Rover and Soil

International audienceThe WISDOM ground-penetrating radar aboard the 2022 ESA-Roscosmos Rosalind-Franklin ExoMars Rover will probe the shallow subsurface of Oxia Planum using electromagnetic waves. A dual-polarized broadband antenna assembly transmits the WISDOM signal into the Martian subsurface and receives the return signal. This antenna assembly has been extensively tested and characterized w.r.t. the most significant antenna parameters (gain, pattern, matching). However, during the design phase, these parameters were simulated or measured without the environment, i.e., in the absence of other objects like brackets, rover vehicle, or soil. Some measurements of the rover's influence on the WISDOM data were performed during the instrument's integration.It was shown that the rover structure and close surroundings in the near-field region of the WISDOM antenna assembly have a significant impact on the WISDOM signal and sounding performance. Hence, it is essential to include the simulations' environment, especially with varying surface and underground.With this contribution, we outline the influences of rover and ground on the antenna's pattern and particularly on the footprint. We employ a 3D field solver with a complete system model above different soil types, i.e., subsurface materials with various combinations of permittivity and conductivity