High circular polarization ratios in radar scattering from geologic targets
High circular polarization ratios in radar scattering from geologic targets
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DOI：
10.1029/2012je004061
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发表时间：
2012-06
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通讯作者：
B. Campbell
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文献类型：
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作者：
B. Campbell
[1]我们研究并模拟了在陆地和行星雷达观测中圆偏振比（CPR或μc）值大于1的情况，作为相关表面形态范围的指导。月球陨石坑沉积物在波长2 ~ 3的12.6和70 cm处μc值最大。金星上麦克斯韦蒙特斯的CPR值在12.6厘米波长下可达1.5左右。亚利桑那州SP Flow的回波在24cm波长处表现出高达2 μc。来自岩石边缘和裂纹（偶极子类）的散射对单次散射产生1 μc，对多次反射产生约2 μc。由成对岩石切面形成的自然角反射面（二面体）散射产生的平均μc为3-4，但可能需要非随机或尺度有限的表面粗糙度才能控制观测到的回波。为了满足最高的月球μc观测，需要二面体机制，而SP Flow和Maxwell Montes的回波可以只用偶极子机制来解释。二面体场景需要岩石表面的尺度是雷达波长的许多倍，而SP Flow的区块（以及麦克斯韦的未知表面纹理）可能无法提供这些。随机偶极子模型在结构和尺度方面要求较低，并且可能通过从岩石和岩石之间散射来增加月球或小行星风化层的CPR。
[1] We examine and model the occurrence of circular polarization ratio (CPR or μc) values greater than unity in terrestrial and planetary radar observations as a guide to the range of associated surface morphology. Lunar crater deposits exhibit maximum μc values at 12.6 and 70-cm wavelength of 2 to 3. CPR values for Maxwell Montes on Venus range up to about 1.5 at 12.6-cm wavelength. Echoes from SP Flow in Arizona exhibit μc up to 2 at 24-cm wavelength. Scattering from rock edges and cracks (dipole-like) produces μc of unity for single scattering and up to about 2 for multiple reflections. Scattering from natural corner reflectors (dihedrals) formed by pairs of rock facets can yield an average μc of 3–4, but likely requires non-random or scale-limited surface roughness properties in order to dominate the observed echo. The dihedral mechanism is required to satisfy the highest lunar μc observations, while echoes from SP Flow and Maxwell Montes could be explained by just the dipole mechanism. The dihedral scenario requires rocky facets on scales many times the radar wavelength, which the blocks at SP Flow (and the unknown surface texture of Maxwell) may not provide. The random dipole model is less demanding in terms of structures and scales, and likely increases the CPR of lunar or asteroid regoliths through scattering from and between rocks.