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Communication Dans Un Congrès Année : 2021

Assessment of the Polarimetric Bandwidth Extrapolation to enhance the resolution of the WISDOM/ExoMars 2022 radar soundings

Nicolas Oudart
  • Fonction : Auteur
Valérie Ciarletti
Alice Le Gall

Résumé

The WISDOM (CNES/DLR) Ground Penetrating Radar (GPR), onboard the ExoMars 2022 Rosalind Franklin rover (ESA/ROSCOSMOS), is designed to study the structure and provide clues on the composition of the shallow Martian subsurface prior to drilling operations (down to a 2 m depth), acquiring key information on the geological context of the samples to be collected, and potential hazards for the drill [1]. To precisely guide this sample collection, the WISDOM instrument was designed with a large bandwidth of 2.5 GHz, allowing soundings with a range resolution of a few cm only in the Martian subsurface, with usual processing (~11 cm in vacuum, the worst case). The use of the Bandwidth Extrapolation (BWE) recently enhanced the vertical resolution of WISDOM radargrams by a factor of 3 [2], reaching a new resolution limit ~3.75 cm, to be compared with the 3 cm length of the samples to be collected. The satisfying performances of the BWE in the reconstruction of radar echoes in time delays and amplitudes have been quantified [3]. The BWE relies on a simple signal model, and its performances could be improved with a more sophisticated one. Thus we studied different modified versions of the BWE, among which the promising Polarimetric Bandwidth Extrapolation (PBWE) [4]. WISDOM having the capacity to transmit and receive signals in 2 orthogonal polarizations, 4 polarimetric channels (2 co-polar and 2 cross-polar) are available when sounding the subsurface. Depending on its geometry and orientation with respect to the antenna system, one echo from a subsurface reflector may appear in different polar channels, but with different complex scattering coefficients. The idea behind the PBWE is to use data from echoes in the different polar channels to more accurately model the signals from each channel. The PBWE was previously applied with success to SAR images on Earth, with improved performances compared to the BWE [5]. We propose here the first application of the PBWE to a planetary GPR, WISDOM, assessing its performances on synthetic soundings (analytical and FDTD simulations, see the Figure) and experimental acquisitions performed in laboratory. [1] Ciarletti et al., Astrobiology, 2017 [2] Cuomo, Lincoln Lab. Report, 1992 [3] Oudart et al., Planetary and Space Science, 2021 [4] Suwa and Iwamoto., IEEE, 2003 [5] Suwa and Iwamoto., IEEE, 2007
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Dates et versions

insu-04425084 , version 1 (29-01-2024)

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Nicolas Oudart, Valérie Ciarletti, Alice Le Gall. Assessment of the Polarimetric Bandwidth Extrapolation to enhance the resolution of the WISDOM/ExoMars 2022 radar soundings. AGU Fall Meeting 2021, Dec 2021, New Orleans, United States. pp.id. P25G-2233. ⟨insu-04425084⟩
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