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Reply to: Stratigraphy versus artefacts in the Chang’e-4 low-frequency radar

Nature Astronomy volume 5, pages 894–897 (2021)Cite this article

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The Original Article was published on 15 September 2021

replying to E. Pettinelli et al. Nature Astronomy https://doi.org/10.1038/s41550-021-01432-x (2021)

We agree that the ATA curves for raw low-frequency data from CE4 and CE3 have similar features, since they were dominated by the strong electromagnetic disturbances and noise that drowned out the relatively weak echoes. The similarity in the major features of the ATA plots computed from the short track (say 10 m) between CE3 and CE4 demonstrates that both LPR payloads are reproducible and almost identical. We computed the ATA curves for CE3 and CE4 using all CE3 data (up to 114 m) and days 1–4 of CE4 (Fig. 1). Our plot confirms their similar overall time-decay trends and the presence of some strong and coincident peaks and troughs between CE3 and CE4. Yet differences in the ATA curves after 1.1 μs of travel time are readily discernible (Fig. 1a). The system disturbance and noise are reproducible and recognizable; hence they can be largely reduced by subtracting the averages traced from each curve. The background-subtracted ATA curves are plotted in Fig. 1b, and the differences between CE3 and CE4 become significant. Furthermore, we compared the ATA plots between two fragments of the Yutu-2 rover track (days 1–4 and 12–16, Fig. 1c). Except for the remaining system noise, which appears as several strong and coincident peaks within the 0.6–1.1 μs travel time, clear echoes from the travel time later than 1.1 μs can be recognized in the ATA plots (Fig. 1).

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Fig. 1: Comparison of the ATA plots between the low-frequency LPR data.
Fig. 2: Comparison of the low-frequency LPR sections of CE3 and CE4 within 0–4 μs travel time.
Fig. 3: The low-frequency LPR section of CE4 acquired over lunar days 1–16 within 0–6 μs travel time.

Data availability

The data used in this work are available via the Science and Application Center for Moon and Deep Space Exploration, Chinese Academy of Sciences (http://moon.bao.ac.cn). Additional data is available from the corresponding author upon request.

Code availability

The codes that support the findings of this study are available from the corresponding author upon reasonable request.

References

  1. Pettinelli, E., Lauro, S. E., Mattei, E., Cosciotti, B. & Soldovieri, F. Stratigraphy versus artefacts in the Chang’e-4 low-frequency radar. Nat. Astron. https://doi.org/10.1038/s41550-021-01432-x (2021).

  2. Zhang, J. et al. Lunar regolith and substructure at Chang’E-4 landing site in South Pole–Aitken basin. Nat. Astron. https://doi.org/10.1038/s41550-020-1197-x (2021).

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Acknowledgements

This work was supported by Key Research Program of Frontier Sciences, Chinese Academy of Sciences (grant number QYZDJ-SSW-DQC001 to Y.L.) and the National Nature Science Foundation of China (grant numbers 41490631 to Y.L. and 41941002 to J.Z.). We thank the Supercomputing Laboratory of IGGCAS for providing computing resources.

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Authors and Affiliations

  1. Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China

    Jinhai Zhang & Yangting Lin

  2. Key Laboratory of Electromagnetic Radiation and Detection Technology, Aerospace Information Research Institute, Chinese Academy of Sciences, Beijing, China

    Bin Zhou

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  1. Jinhai Zhang
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Y.L. led the study, J.Z. and B.Z. processed and analysed the LPR data and all authors prepared the paper.

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Correspondence to Yangting Lin.

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Zhang, J., Zhou, B. & Lin, Y. Reply to: Stratigraphy versus artefacts in the Chang’e-4 low-frequency radar. Nat Astron 5, 894–897 (2021). https://doi.org/10.1038/s41550-021-01484-z

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