Horváth Gábor, Hegedüs Ramón, Barta András, Farkas Alexandra, Åkesson Susanne
Environmental Optics Laboratory, Department of Biological Physics, Physical Institute, Eötvös University, Budapest, Hungary.
Appl Opt. 2011 Oct 1;50(28):F64-71. doi: 10.1364/AO.50.000F64.
The knowledge on the optics of fogbows is scarce, and their polarization characteristics have never been measured to our knowledge. To fill this gap we measured the polarization features of 16 fogbows during the Beringia 2005 Arctic polar research expedition by imaging polarimetry in the red, green and blue spectral ranges. We present here the first polarization patterns of the fogbow. In the patterns of the degree of linear polarization p, fogbows and their supernumerary bows are best visible in the red spectral range due to the least dilution of fogbow light by light scattered in air. In the patterns of the angle of polarization α fogbows are practically not discernible because their α-pattern is the same as that of the sky: the direction of polarization is perpendicular to the plane of scattering and is parallel to the arc of the bow, independently of the wavelength. Fogbows and their supernumeraries were best seen in the patterns of the polarized radiance. In these patterns the angular distance δ between the peaks of the primary and the first supernumerary and the angular width σ of the primary bow were determined along different radii from the center of the bow. δ ranged between 6.08° and 13.41°, while σ changed from 5.25° to 19.47°. Certain fogbows were relatively homogeneous, meaning small variations of δ and σ along their bows. Other fogbows were heterogeneous, possessing quite variable δ- and σ-values along their bows. This variability could be a consequence of the characteristics of the high Arctic with open waters within the ice shield resulting in the spatiotemporal change of the droplet size within the fog.
关于雾虹光学的知识匮乏，就我们所知，其偏振特性从未被测量过。为填补这一空白，我们在2005年白令海北极极地研究考察期间，通过在红、绿、蓝光谱范围内进行成像偏振测量，测量了16条雾虹的偏振特征。我们在此展示雾虹的首张偏振图样。在线性偏振度p的图样中，由于雾虹光在空气中散射光的稀释作用最小，雾虹及其附属虹在红光谱范围内最为清晰可见。在偏振角α的图样中，雾虹实际上难以辨别，因为它们的α图样与天空的相同：偏振方向垂直于散射平面且平行于虹弧，与波长无关。雾虹及其附属虹在偏振辐射图样中最为清晰可见。在这些图样中，沿着从虹中心出发的不同半径，确定了主虹和第一附属虹峰值之间的角距离δ以及主虹的角宽度σ。δ在6.08°至13.41°之间，而σ从5.25°变化到19.47°。某些雾虹相对均匀，意味着沿着虹的δ和σ变化较小。其他雾虹则不均匀，沿着虹具有相当可变的δ值和σ值。这种变化可能是由于北极高纬度地区冰盖内有开阔水域，导致雾中液滴大小的时空变化所致。
