Mishchenko Michael I
NASA Goddard Institute for Space Studies, New York, New York 10025, USA.
Opt Express. 2010 Sep 13;18(19):19770-91. doi: 10.1364/OE.18.019770.
This paper solves the long-standing problem of establishing the fundamental physical link between the radiative transfer theory and macroscopic electromagnetics in the case of elastic scattering by a sparse discrete random medium. The radiative transfer equation (RTE) is derived directly from the macroscopic Maxwell equations by computing theoretically the appropriately defined so-called Poynting-Stokes tensor carrying information on both the direction, magnitude, and polarization characteristics of local electromagnetic energy flow. Our derivation from first principles shows that to compute the local Poynting vector averaged over a sufficiently long period of time, one can solve the RTE for the direction-dependent specific intensity column vector and then integrate the direction-weighted specific intensity over all directions. Furthermore, we demonstrate that the specific intensity (or specific intensity column vector) can be measured with a well-collimated radiometer (photopolarimeter), which provides the ultimate physical justification for the use of such instruments in radiation-budget and particle-characterization applications. However, the specific intensity cannot be interpreted in phenomenological terms as signifying the amount of electromagnetic energy transported in a given direction per unit area normal to this direction per unit time per unit solid angle. Also, in the case of a densely packed scattering medium the relation of the measurement with a well-collimated radiometer to the time-averaged local Poynting vector remains uncertain, and the theoretical modeling of this measurement is likely to require a much more complicated approach than solving an RTE.
本文解决了一个长期存在的问题，即在稀疏离散随机介质弹性散射的情况下，建立辐射传输理论与宏观电磁学之间的基本物理联系。通过理论计算适当定义的所谓坡印廷 - 斯托克斯张量，该张量携带有关局部电磁能流的方向、大小和极化特性的信息，直接从宏观麦克斯韦方程组推导出辐射传输方程（RTE）。我们从第一原理出发的推导表明，为了计算在足够长的时间内平均的局部坡印廷矢量，人们可以求解与方向相关的比强度列矢量的RTE，然后在所有方向上对方向加权的比强度进行积分。此外，我们证明比强度（或比强度列矢量）可以用准直良好的辐射计（光偏振计）测量，这为在辐射预算和粒子表征应用中使用此类仪器提供了最终的物理依据。然而，比强度不能从现象学角度解释为表示在给定方向上垂直于该方向的单位面积、单位时间、单位立体角内传输的电磁能量。而且，在密集堆积的散射介质的情况下，用准直良好的辐射计进行的测量与时间平均局部坡印廷矢量之间的关系仍然不确定，并且这种测量的理论建模可能需要比求解RTE复杂得多的方法。
