Uncertainty Quantification in SuperCam IRS Data: A Bayesian MCMC Approach

At IAS, I developed a Bayesian MCMC approach to analyze infrared spectra from NASA’s Perseverance rover. By coupling radiative transfer modeling with advanced optimization, I improved mineralogical fits and quantified uncertainties—gaining hands-on experience at the crossroads of planetary science, numerical methods, and space exploration.

image of a space exploration interface in holographic display
INTERNSHIP INSIGHT

TYPE

Research laboratory

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COMPANY

Institut d'Astrophysique Spatiale (IAS)

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YEAR

2024

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DURATION

3 months

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LOCATION

Orsay, FRANCE

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LINK

https://www.ias.u-psud.fr

INTERNSHIP DETAILS

Context and Objectives

During summer 2024 (June 3 – August 30, 2024), I completed a research internship as an assistant engineer within the Planetology team at the IAS (Institut d’Astrophysique Spatiale), under the supervision of Dr. François Poulet and Dr. Clément Royer. My work was part of the Mars 2020 mission: I focused on data from the passive infrared spectrometer IRS / SuperCam onboard the Perseverance rover, with the objective of improving the reflectance spectra fitting procedure in order to estimate mineralogy (abundances, grain sizes) and—most importantly—quantify the uncertainties associated with inferred parameters.

INTERNSHIP DETAILS

Methodological Approach

The core of the project was to couple a radiative transfer model (Shkuratov model) with a Bayesian optimization procedure (MCMC) to extract parameter distributions from Martian spectra. My tasks combined numerical optimization (improving a simplex / Nelder-Mead method), implementation and testing of MCMC samplers (affine-invariant ensemble sampler), and systematic validation on laboratory spectra before applying the approach to Martian targets.

INTERNSHIP DETAILS

Work Completed (Key Points)

  • Simplex optimization: rewrote and adapted a simplex method to handle physical constraints and bounds (abundances, grain sizes), added a penalty term to the cost function to enforce the constraint ∑ abundances = 1, and implemented a probabilistic reset to mitigate local minima.
  • Laboratory spectra testing: validated the procedure on known mixtures (magnesite / nontronite / olivine), which revealed and allowed correction of biases (notably a simple multiplicative gain factor ≈0.9 applied to the real spectrum, significantly improving RMS fits). In some laboratory cases, RMS dropped from ~1.11% to 0.47% after correction.
  • Application to Martian targets: applied the improved method to Martian sites (e.g., Hastaa — Sol106 and Chiniak — Sol565), testing different mineral lists and analyzing the robustness of MCMC-derived distributions (4000 iterations, 40 walkers in the runs presented).

INTERNSHIP DETAILS

Results and Interpretations

  • Fit quality: the procedure produced highly satisfactory fits (typical RMS ≈ 0.16–0.28% for individual targets; average RMS ≈ 0.19% for Hastaa), demonstrating the pipeline’s ability to accurately reproduce spectral signatures.
  • Average composition (Hastaa): statistical analysis of 10 Hastaa targets showed a high proportion of olivine (Olivine Fo40 + Fo70 ≈ ~47% total, dominated by Fo40 ≈ 37%), pyroxenes (Augite + Pigeonite ≈ ~35%), and ~18% aqueous alteration minerals (Nontronite + Serpentine), confirming evidence of aqueous alteration at the studied location.
  • Methodological insights: several phenomena emerged (degeneracy between grain size and abundance for certain minerals, sensitivity to local spectral offsets, need to adjust the weighting of specific bands), suggesting avenues for further improvement (tempered MCMC, alternative samplers, refined spectral calibration).

INTERNSHIP DETAILS

Skills Developed

  • Technical / Scientific: radiative transfer modeling (Shkuratov), spectral fitting methodologies, Martian spectral interpretation.
  • Computational: Python programming (scipy, implementation of optimization algorithms and MCMC), handling of numerical constraints and cost function optimization.
  • Methodological & Soft Skills: critical reading of scientific literature, autonomous project management (balancing theory and practice), communicating results to supervisors and the research team.

INTERNSHIP DETAILS

Personal Assessment and Perspectives

This internship was a valuable immersion in space research, allowing me to bridge advanced numerical methods with real scientific questions (uncertainty quantification, robustness of inferences). The experience confirmed my intention to pursue a Master’s in Astrophysics and gave me concrete ideas for extending this work (further optimization of the MCMC algorithm, extended validation, contribution to instrument calibration).

Want to Know More?

Download the full internship report for in-depth
technical documentation and detailed findings.

Project report
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image of engineers working on satellite components [team]
image of engineers working on satellite components [team]
image of engineers working on satellite components [team]
image of engineers working on satellite components [team]
image of engineers working on satellite components [team]
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