Presentation Information
[PPS02-P10]Numerical Analysis of Lunar Surface Roughness Effects on Terahertz Observations
*Tomohiro Takemura1, Hideaki Miyamoto1, Makito Kobayashi1 (1.The University of Tokyo)
Keywords:
Moon,Terahertz wave,TSUKIMI,water ice
The Lunar Terahertz SUrveyor for KIlometer scale MappIng (TSUKIMI) mission aims to estimate the thermophysical and dielectric properties of the shallow lunar subsurface in the terahertz frequency range and to identify regions enriched in water ice and metallic materials. TSUKIMI primarily derives apparent dielectric permittivity from observations of the polarization ratio and identifies potential enrichment regions of water ice and metallic materials by examining relative spatial variations in dielectric properties. However, the observed polarization ratio and inferred apparent dielectric permittivity are known to vary not only with the presence of water ice or metallic materials but also with regolith conditions such as bulk density and temperature (e.g., Heiken et al., 1991). In particular, surface roughness can strongly influence terahertz emission and scattering behavior, potentially causing significant variations in the observed polarization ratio and estimated dielectric permittivity (e.g., Cai and Fa, 2020; Guo et al., 2021). However, the effects of lunar surface roughness at terahertz wavelength scales, on the order of several hundred micrometers to several millimeters, have not been comprehensively quantified.
In this study, we conduct laboratory experiments that simulate lunar surface roughness and develop numerical models that reproduce the response of terahertz waves to surface topography in order to evaluate the impact of lunar surface roughness on TSUKIMI polarization observations. In particular, we perform an initial assessment of whether regions enriched in water ice or metallic materials can still be identified based on the polarization ratio and the derived apparent dielectric permittivity, even in the presence of surface roughness effects.
First, we experimentally investigate the influence of surface roughness at terahertz wavelength scales on emission and scattering behavior. Lunar regolith simulants are used to reproduce representative lunar surface roughness, and polarization ratio measurements are conducted using the breadboard model of the terahertz sensor employed in TSUKIMI observations. In parallel, we construct numerical models based on the Advanced Integral Equation Model to evaluate variations in the polarization ratio as a function of surface roughness conditions.
The laboratory experiments indicate that, even in the presence of millimeter to centimeter scale surface roughness expected for the lunar regolith, it may be possible to distinguish regions enriched in water ice or metallic resources from polarization ratio observations (Kobayashi et al., 2025). Furthermore, numerical model analyses suggest that, even under average surface roughness conditions representative of the Chang'E-4 landing site, TSUKIMI observations may be capable of resolving an apparent dielectric permittivity difference of 0.2, provided that the sensor performance is maintained within its nominal temperature range. In this presentation, we will report the details of the laboratory experiments and numerical modeling, along with perspectives for future work.
Acknowledgments
This work was supported by the Space Strategy Fund (SSF) of the Japan Aerospace Exploration Agency (JAXA) under Grant No. JPJXSSF25SS03001. It also includes results obtained from the Ministry of Internal Affairs and Communications “R&D Program on ICT Priority Technologies” (JPMI00316) under the project “Wide Area Exploration of Lunar Water and Energy Resources Using Terahertz Waves” (JPJ010777).
References:
Heiken et al. (1991), Lunar Sourcebook: A User’s Guide to the Moon, Cambridge University Press.
Cai and Fa (2020), Journal of Geophysical Research: Planets, 125(8), e2020JE006429.
Guo et al. (2021), Geophysical Research Letters, 48(19), e2021GL094931.
Kobayashi et al. (2025), The Planetary Science Journal, 6(11), 266.
In this study, we conduct laboratory experiments that simulate lunar surface roughness and develop numerical models that reproduce the response of terahertz waves to surface topography in order to evaluate the impact of lunar surface roughness on TSUKIMI polarization observations. In particular, we perform an initial assessment of whether regions enriched in water ice or metallic materials can still be identified based on the polarization ratio and the derived apparent dielectric permittivity, even in the presence of surface roughness effects.
First, we experimentally investigate the influence of surface roughness at terahertz wavelength scales on emission and scattering behavior. Lunar regolith simulants are used to reproduce representative lunar surface roughness, and polarization ratio measurements are conducted using the breadboard model of the terahertz sensor employed in TSUKIMI observations. In parallel, we construct numerical models based on the Advanced Integral Equation Model to evaluate variations in the polarization ratio as a function of surface roughness conditions.
The laboratory experiments indicate that, even in the presence of millimeter to centimeter scale surface roughness expected for the lunar regolith, it may be possible to distinguish regions enriched in water ice or metallic resources from polarization ratio observations (Kobayashi et al., 2025). Furthermore, numerical model analyses suggest that, even under average surface roughness conditions representative of the Chang'E-4 landing site, TSUKIMI observations may be capable of resolving an apparent dielectric permittivity difference of 0.2, provided that the sensor performance is maintained within its nominal temperature range. In this presentation, we will report the details of the laboratory experiments and numerical modeling, along with perspectives for future work.
Acknowledgments
This work was supported by the Space Strategy Fund (SSF) of the Japan Aerospace Exploration Agency (JAXA) under Grant No. JPJXSSF25SS03001. It also includes results obtained from the Ministry of Internal Affairs and Communications “R&D Program on ICT Priority Technologies” (JPMI00316) under the project “Wide Area Exploration of Lunar Water and Energy Resources Using Terahertz Waves” (JPJ010777).
References:
Heiken et al. (1991), Lunar Sourcebook: A User’s Guide to the Moon, Cambridge University Press.
Cai and Fa (2020), Journal of Geophysical Research: Planets, 125(8), e2020JE006429.
Guo et al. (2021), Geophysical Research Letters, 48(19), e2021GL094931.
Kobayashi et al. (2025), The Planetary Science Journal, 6(11), 266.