Site-dependent bulk permittivities of the lunar uppermost media with thicknesses of tens to hundreds meters were estimated based on the data from Lunar Radar Sounder onboard the Selenological and Engineering Explorer (SELENE). It succeeded in sounding almost all over the Moon’s surface in a frequency range around 5 MHz to detect subsurface reflectors beneath several lunar maria. However, it is necessary to estimate the permittivity of the surface regolith of the Moon in order to determine the actual depths to those reflectors instead of apparent depths assuming a speed of light in the vacuum. In this study, we determined site-dependent bulk permittivities by two-layer models consisting of a surface regolith layer over a half-space with uniform, but different physical properties from the layer above. Those models consider the electrical conductivity as well as the permittivity, whose trade-off was resolved by utilizing the correlation between iron–titanium content and measured physical properties of lunar rock samples. Distribution of the iron–titanium content on the Moon’s surface had already been derived by spectroscopic observation from SELENE as well. Four lunar maria, Mare Serenitatis, Oceanus Procellarum, Mare Imbrium, and Mare Crisium, were selected as regions of evident reflectors, where we estimated the following four physical properties of each layer, i.e., bulk permittivity, porosity, loss tangent and electrical conductivity to conclude the actual depths of the reflectors are approximately 200 m on average. The bulk permittivity ranges from 2.96 at Mare Imbrium to 6.37 at Oceanus Procellarum, whereas the porosity takes the values between 1.8 and 41.1% in the respective maria. It was found that although the bulk permittivity of the four lunar maria differs from a mare to a mare, it shows a good correlation with their composition, viz., their iron–titanium content.

中文翻译：

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使用月球雷达测深仪车载硒学和工程探索器估算月球表面的体介电常数

厚度为数十至数百米的月球最上层介质的与场地相关的体积介电常数是根据来自硒学和工程探索者 (SELENE) 上的月球雷达测深仪的数据估算的。它成功地在大约 5 MHz 的频率范围内探测了几乎整个月球表面，以探测到几个月海下的地下反射体。然而，有必要估计月球表面风化层的介电常数，以确定这些反射器的实际深度，而不是假设真空中光速的表观深度。在这项研究中，我们通过两层模型确定了与位置相关的体介电常数，该模型由半空间上的表面风化层组成，具有均匀但与上层不同的物理特性。这些模型考虑了电导率和介电常数，通过利用铁钛含量与月球岩石样品的测量物理特性之间的相关性来解决其权衡问题。月球表面铁钛含量的分布也已经通过 SELENE 的光谱观察得出。选择了四个月海，即 Mare Serenitatis、Oceanus Procellarum、Mare Imbrium 和 Mare Crisium 作为明显反射体的区域，我们估计了每一层的以下四个物理特性，即体介电常数、孔隙率、损耗角正切和电导率以得出结论，反射器的实际深度平均约为 200 m。大容量介电常数范围从雨海的 2.96 到 Oceanus Procellarum 的 6.37，而孔隙率在相应的玛丽亚中取值介于 1.8% 和 41.1% 之间。研究发现，虽然四个月海的体积介电常数因母马而异，但与它们的成分（即铁钛含量）显示出良好的相关性。