11:00 〜 13:00
[PPS06-P07] Numerical Study on Terahertz Emission from the Lunar Surface
キーワード：Lunar exploration, terahertz, scattering and emission
In a collaborative effort to bridge the gap in both lunar exploration and electromagnetic spectrum, our research group is initiating a terahertz lunar exploration mission, named as Lunar Terahertz SUrveyor for KIlometer-scale MappIng (TSUKIMI), led by the National Institute of Information and Communications Technology (NICT) and collaborated with the University of Tokyo, Japan Aerospace Exploration Agency (JAXA), Osaka Prefecture University, and the SpaceBD company. One of the key milestones of this main mission is to develop a micro-satellite terahertz radiometer with the agilities of dual-frequency, dual-polarization, and multi-angle observation for lunar exploration. It attempts to monitor the lunar brightness temperature spatiotemporally on the global scale and retrieve the physical parameters of the lunar surface and subsurface, including dielectric constant, water distribution map, mineralogy resource, and topographic roughness others.
In support of the TSUKIMI mission, we investigate the terahertz emission model with the consideration of the rough surface scattering effect from the lunar surface, which is characterized by a power-law roughness spectrum and inhomogeneous dielectric profile. To better understand the physical mechanism of the terahertz emission from the lunar surface, the effects of root-mean-square (RMS) height, correlation length, dielectric constant, and probing frequency, polarization, and observation angle were investigated, covering a wide range of lunar dielectric properties and lunar rough surface conditions. Numerical results indicate that the diffuse scattering is enhanced when the RMS height increases, particularly in backscattering. As the correlation length increases, the scattering coefficients decrease with the incident angle and increase to a larger value at small angles of incidence, manifests a strong incidence dependence. Furthermore, we found that the lunar surface emissivity has dependence on its dielectric constant, under which the identical surface roughness condition, the emissivity decreases accordingly as the dielectric constant increases, for both H and V polarizations. Meanwhile, the H-polarized emissivity is more sensitive to the dielectric change than the V-polarized emissivity in the simulation range of the observation angle, namely, 10 degree to 60 degree, in particular at large observation angle ranging from 40 degree to 60 degree, V-polarized emissivity eventually shows less sensitivity to the surface roughness and dielectric property. It signifies that the V-polarized brightness temperature at the large observation angle offers a promising potential to accurately estimate the surface temperature since it shows less dependence on the surface emissivity, which is mainly determined by the dielectric constant and surface roughness. Thus, in turn, it demonstrates a reliable forward model can help in optimizing the observation configuration, understanding the scattering and emission mechanisms and developing retrieval algorithms for the parameters of interest.
In support of the TSUKIMI mission, we investigate the terahertz emission model with the consideration of the rough surface scattering effect from the lunar surface, which is characterized by a power-law roughness spectrum and inhomogeneous dielectric profile. To better understand the physical mechanism of the terahertz emission from the lunar surface, the effects of root-mean-square (RMS) height, correlation length, dielectric constant, and probing frequency, polarization, and observation angle were investigated, covering a wide range of lunar dielectric properties and lunar rough surface conditions. Numerical results indicate that the diffuse scattering is enhanced when the RMS height increases, particularly in backscattering. As the correlation length increases, the scattering coefficients decrease with the incident angle and increase to a larger value at small angles of incidence, manifests a strong incidence dependence. Furthermore, we found that the lunar surface emissivity has dependence on its dielectric constant, under which the identical surface roughness condition, the emissivity decreases accordingly as the dielectric constant increases, for both H and V polarizations. Meanwhile, the H-polarized emissivity is more sensitive to the dielectric change than the V-polarized emissivity in the simulation range of the observation angle, namely, 10 degree to 60 degree, in particular at large observation angle ranging from 40 degree to 60 degree, V-polarized emissivity eventually shows less sensitivity to the surface roughness and dielectric property. It signifies that the V-polarized brightness temperature at the large observation angle offers a promising potential to accurately estimate the surface temperature since it shows less dependence on the surface emissivity, which is mainly determined by the dielectric constant and surface roughness. Thus, in turn, it demonstrates a reliable forward model can help in optimizing the observation configuration, understanding the scattering and emission mechanisms and developing retrieval algorithms for the parameters of interest.