The Continuum Slope of Mars: Bidirectional Reflectance Investigations and Applications to Olympus Mons
The Continuum Slope of Mars: Bidirectional Reflectance Investigations and Applications to Olympus Mons
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火星的连续坡度：双向反射研究及其在奥林匹斯山的应用
DOI：
10.1006/icar.1993.1043
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发表时间：
1993
期刊：
影响因子：
3.2
通讯作者：
C. Pieters
中科院分区：
文献类型：
--
作者：
E. M. Fischer;C. Pieters
摘要对于火星，近红外连续光谱经常被观察到对较长波长的反射率降低。这种负的连续斜率与亮区和暗区都有关，但在后者中更为明显。通过实验研究了黑色基体上细颗粒铁涂层的连续谱斜率特性。负连续斜率的几个相互关联的原因包括在深色基底上存在非常薄的铁涂层以及取决于表面纹理、观察几何形状和波长的反射行为。这种反射行为的特征在于在正向方向上较长波长的优先反射，并且对于紧密堆积的颗粒表面、具有非常小的颗粒尺寸的材料、以及对于在所测量的光的波长的量级或小于所测量的光的波长的量级上的其他光滑表面，在不同程度上观察到这种反射行为。当在后向散射几何形状下观察时，这种波长依赖的定向反射率产生负连续斜率。连续体斜率的变化是由不同的铁涂层厚度、不同的表面纹理和不同的测量几何形状引起的。奥林匹斯山地区的ISM成像光谱仪数据揭示了火山侧翼及其附近的环和弧形式的表面特征，这些特征由空间相干的连续斜率值定义。这些ISM数据提供了一个独特的机会，以评估薄铁涂层实验的背景下，火星表面特性的空间变化。光谱环和弧的空间分布是一致的风成输送颗粒和形成的硬壳或硬壳状的表面纹理。
Abstract For Mars, the near-infrared continuum is often observed to decrease in reflectance toward longer wavelengths. This negative continuum slope is associated with both bright and dark regions, but is much more pronounced in the latter. Laboratory experiments were performed to investigate the properties of the continuum slope for thin ferric coatings of fine particles on dark substrates. Several interrelated causes of the negative continuum slope include the presence of very thin ferric coatings on dark substrates and reflectance behavior that is dependent on surface texture, viewing geometry, and wavelength. This reflectance behavior is characterized by the preferential reflectance of longer wavelengths in the forward direction and is observed to various degrees for tightly packed particulate surfaces, for materials with very small grain-sizes, and for surfaces otherwise smooth on the order of or smaller than the wavelength of the measured light. This wavelength-dependent directional reflectance produces a negative continuum slope when viewed at backscattering geometries. Variations in continuum slope are caused by varying ferric coating thickness, varying surface texture, and varying geometry of the measurement. The ISM imaging spectrometer data of the Olympus Mons region reveal surface features in the form of annuli and arcs on and near the flanks of the volcano that are defined by spatially coherent continuum slope values. These ISM data provide a unique opportunity to evaluate the spatial variation of Martian surface properties in the context of the thin ferric coatings experiments. The spatial distribution of the spectral annuli and arcs is consistent with eolian transported particulates and with the formation of duricrust or duricrust-like surface texture.