Chang’E4 Lunar Penetrating Radar dataset now easily and fully available: new perspectives and opportunities for the moon exploration

Data processing of the Lunar Penetrating Radar dataset, validation and format conversion to improve the links between the planetary and the geophysical community.
Chang’E4 Lunar Penetrating Radar dataset now easily and fully available: new perspectives and opportunities for the moon exploration
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LPR Data processing

Chinese lunar landing mission Chang'E-4 reached the far side of the Moon in January 2019 and is the first soft landing and in-site detection mission on the far side of the Moon.  Since 2019 the two channels Lunar Penetrating Radar (LPR) onboard the landed Yutu-2 rover is recording unprecedented data investigating the lunar subsurface (Dong et al., 2021). The rover traveled for more than 1400 m on the moon surface and is still working. Data are periodically released to the scientific community in separated files by the Lunar and Planetary data release system (https://moon.bao.ac.cn/ce5web/moonGisMap.search) of the National Astronomical Observatories of China. Until January 2024, 160 separated LPR data files have been released, as well as several additional data coming from the other scientific payloads of the Mission (Jia et al., 2018).
In order to extract all the information embedded within the LPR dataset (considering here only the high frequency channel of LPR), some preliminary steps are mandatory. In particular, we addressed the peculiar problem related to duplicated traces and data file stitching. In fact, the rover makes several stops to acquire several different measurements during its movement without interrupting the acquisition of LPR data. As a consequence, most of the raw data are redundant and must be removed (Lai et al., 2021). Since the accuracy of recorded coordinates is not high enough, we have designed an algorithm capable of automatically recognizing and removing duplicated scans, minimizing the subjectivity of the procedure, saving time, and avoiding possible residual duplications. From an original LPR dataset of 634,419 A-scans (i.e. LPR traces), after duplication removal we retained 40,022 A-scans (i.e. about 6%) without losing any essential information and making data analysis faster and more straightforward.
Dataset was processed applying a typical flow including bandpass filter, zero-time correction, background removal, exponential amplitude compensation, topographic correction and depth conversion. Results are given in different formats to make it fully available for different user communities. In particular, we provide the same data in two different formats (namely: PDS4 and SEG-Y) and three different versions (namely: filtered from redundant repeated data; processed in time without topographic correction, and processed in depth with topographic correction).
As far as the format, While PDS4 is a format used primarily by NASA to store and distribute solar, lunar and planetary imagery data (https://pds.nasa.gov/datastandards/documents/), SEG-Y is the standard format developed by the Society of Exploration Geophysicists (SEG) to store reflection seismic geophysical data (http://seg.org/Publications/SEG-Technical-Standards) but can be conveniently used even for Ground Penetrating Radar datasets. In this way, both the planetology/space and geophysical communities can easily manage the data taking advantage by applying the most common processing, inversion, interpretation, integration algorithms and software.
After an accurate technical validation, including lateral continuity analysis of the reflectors and correct data opening checking on the most common commercial and readability of the and open-source programs, all the datasets have been disclosed to the public usage and made freely available to the scientific community (PDS4: https://doi.org/10.6084/m9.figshare.23723976.v1 and SEG-Y: https://doi.org/10.6084/m9.figshare.23723922.v1). Future data releases can be straightforwardly added to the present-day dataset. A similar approach and the codes downloadable can be easily directly applied or adapted for other radar datasets now available (e.g. of Chang’E3 or Chang’E5 lunar missions or to the ongoing radar missions on Mars).

Final processed CE-4 LPR dataset (split in two separate sections just for a better visualization) obtained after the application of the complete processing flow described in the article.

In the future…
Despite several interpretations of Chang’E4 LPR high frequency dataset have been already published (e.g. Lai et al., 2021; Zhang et al., 2021; Chen et al., 2022; Feng et al, 2022), some of them are limited on the first few hundred meters, while even the more recent (Feng et al., 2023; Giannakis et al., 2024) do not exceed 1 km in length.
With the new comprehensive edited dataset, provided in different processing steps and versions, we hope that the international community will have ready-to-use benchmark data (PDS4: https://doi.org/10.6084/m9.figshare.23723976.v1 and SEG-Y: https://doi.org/10.6084/m9.figshare.23723922.v1) and codes (https://github.com/Giacomo-Roncoroni/LPR_CE4) to be exploited in order to obtain more objective, constrained and comparable results.

For access to the Chang’E4 dataset, we recommend first reading the article which provides technical details and additional data links: https://doi.org/10.1038/s41597-024-02963-4

References
Chen, R. et al. Sub-surface stratification and dielectric permittivity distribution at the Chang’E-4 landing site revealed by the Lunar
Penetrating Radar. Astron. Astrophys. 664 (2022).
Dong, Z. et al. Properties of lunar regolith on the Moon’s farside unveiled by Chang’E‐4 Lunar Penetrating Radar. J. Geophys. Res.
Planets 126 (2021).
Feng, J., Siegler, Matthew. A. & White, M.N. Dielectric properties and stratigraphy of regolith in the lunar South Pole-Aitken basin: observations from the Lunar Penetrating Radar. Astron. Astrophys. 661 (2022).
Feng, J., et al. Layered structures in the upper several hundred meters of the moon along the Chang’E-4 rover’s first 1,000-m traverse. Journal of Geophysical Research: Planets, 128 (8), e2022JE007714 (2023).
Giannakis, I., et al. Evidence of shallow basaltic lava layers in Von Kármán crater from Yutu-2 Lunar Penetrating Radar. Icarus, 408, 115837 (2024).
Jia, Y. et al. The scientific objectives and payloads of Chang’E−4 mission. Planet. Space Sci. 162, 207–215 (2018).
Lai, J. et al. A complex paleo‐surface revealed by the Yutu‐2 rover at the lunar farside. Geophys. Res. Lett. 48 (2021).

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