Bidirectional reflectance spectroscopy 8. The angular width of the opposition effect in regolith-like media
Bidirectional reflectance spectroscopy 8. The angular width of the opposition effect in regolith-like media
复制标题
双向反射光谱8.类风化介质中相反效应的角宽度
DOI：
10.1016/j.icarus.2020.114105
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发表时间：
2021
期刊：
影响因子：
3.2
通讯作者：
B. Hapke
中科院分区：
文献类型：
--
作者：
B. Hapke
反向效应是在零相位角附近的散射介质的反射率中观察到的尖锐、窄的浪涌。大量的观察和实验表明，在颗粒介质中的现象的主要原因是相干后向散射，其中在相反的方向上行进的子波沿着链的散射相长干涉，并产生峰值。一个更广泛的反对浪潮所造成的阴影隐藏和优先逃逸也存在，但纠缠与相干峰叠加的非相干连续反射，使其难以识别和隔离。独立散射体介质的理论模型预测相干后向散射峰的角宽度和形状取决于波长、孔隙率和颗粒尺寸。人们希望，对对冲效应的远程测量将提供行星风化层中后两个量的信息。然而，对相互接触的大颗粒介质的观察和实验室研究发现，这些量几乎没有依赖性。相反，这些研究意味着在风化层介质中的对抗效应来自于短链的反射，这些短链只有几个散射体长位于介质颗粒的表面上，并且这些链的长度与波长成正比。由于峰的角宽度由波长与平均散射链长度的比率控制，因此宽度与波长无关。因为子波从不进入粒子，所以低相干介质可以表现出强相干反向散射峰。在太阳系天体上，对置效应峰宽度小于一度的可能意味着未成熟的风化层，而数度宽的峰则意味着成熟的风化层。
The opposition effect is the sharp, narrow surge observed in the reflectance of a scattering medium near zero phase angle. Numerous observations and experiments have shown that the primary cause of the phenomenon in particulate media is coherent backscattering, in which wavelets traveling in opposite directions along chains of scatterers interfere constructively and generate the peak. A broader opposition surge caused by shadow hiding and preferential escape is also present, but is entangled with the incoherent continuum reflectance on which the coherent peak is superposed, making it difficult to identify and isolate. Theoretical models of media of independent scatterers predict that the angular width and shape of the coherent backscatter peak depend on the wavelength, porosity and particle size. It was hoped that remote measurements of the opposition effect would give information on the latter two quantities in planetary regoliths. However, observations and laboratory studies of media of large particles in contact with one another find little dependence on any of these quantities. Instead, these studies imply that the opposition effect in regolith-like media comes from reflection by short chains only a few scatterers long located on the surfaces of the particles of the medium, and that the lengths of these chains are proportional to the wavelength. Since the angular width of the peak is controlled by the ratio of the wavelength to the mean scattering chain length, the width is independent of wavelength. Because the wavelets never enter a particle, low albedo media can exhibit a strong coherent backscatter peak. Opposition effect peaks less than a degree wide on solar system bodies can imply an immature regolith; peaks several degrees wide imply a mature regolith.