作为相位函数的B、V、R和I波段地照偏振的测量
Measurement of the earthshine polarization in the B, V, R, and I band as function of phase
摘要：
描述行星地球的偏振特性对于解释预期的观测结果和规划未来的仪器都很重要。我们提出了一个多波长和多相位的基准值的偏振信号的综合光从行星地球来自新的偏振观测的地球反射回散射从月球的黑暗面。使用一种新的，专门设计的宽场偏振计，我们测量了地球相位角α在30°和110°之间的B，V，R和I过滤器中的地照的部分偏振。地照光偏振的相位依赖关系可以用函数p x sin（alpha）^[2]拟合。为了确定地球的偏振，我们校正我们的地球反射测量的偏振效率函数的月球表面来自月球样品的测量文献。地照光的偏振度随着波长的增加而减小，在海拔较高的阿雷格里多高地，偏振度大约是原来的1.3倍。对于海区，在B波段正交处测得的最大偏振度约为13%.由此产生的地球的分数极化为B波段24.6%，V波段19.1%，R波段13.5%，I波段8.3%。结合地球光谱反射率的文献值，我们得到了地球偏振通量和太阳（总）通量之间的对比，不确定度小于20%，我们发现探测地球孪生子的最佳相位是在地球相位α =65°附近。Stam（2008）的类地行星的偏振模型与我们的结果定性一致，但也存在显着差异，可能会指导更详细的计算。
英文摘要：
The characterization of the polarimetric properties of the planet Earth is important for the interpretation of expected observations and the planning of future instruments. We present a multi-wavelengths and multi-phase set of benchmark values for the polarization signal of the integrated light from the planet Earth derived from new polarimetric observations of the earthshine back-scattered from the Moon's dark side. Using a new, specially designed wide field polarimeter we measured the fractional polarization of the earthshine in the B, V, R and I filters for Earth phase angles alpha between 30° and 110°. The phase dependence of the earthshine polarization is fitted by a function p x sin(alpha)^2. To determine the polarization of the planet Earth we correct our earthshine measurements by a polarization efficiency function for the lunar surface derived from measurements of lunar samples from the literature. The polarization of the earthshine decreases towards longer wavelengths and is about a factor 1.3 lower for the higher albedo highlands. For mare regions the measured maximum polarization is about 13 % at quadrature in the B band. The resulting fractional polarizations for Earth are 24.6 % for the B band, 19.1 % for the V band, 13.5 % for the R band, and 8.3 % for the I band. Together with literature values for the spectral reflectivity of Earth we obtain a contrast between the polarized flux of the Earth and the (total) flux of the Sun with an uncertainty of less than 20 % and we find that the best phase to detect an Earth twin is around an Earth phase alpha=65°. The polarimetric models of Earth-like planets from Stam (2008) are in qualitative agreement with our results but there are also significant differences which might guide more detailed computations.
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