Geissler P, Thompson W R, Greenberg R, Moersch J, McEwen A, Sagan C
Lunar and Planetary Laboratory, University of Arizona, Tucson, USA.
J Geophys Res. 1995 Aug 25;100(E8):16895-906. doi: 10.1029/95je01407.
Nearly 6000 multispectral images of Earth were acquired by the Galileo spacecraft during its two flybys. The Galileo images offer a unique perspective on our home planet through the spectral capability made possible by four narrowband near-infrared filters, intended for observations of methane in Jupiter's atmosphere, which are not incorporated in any of the currently operating Earth orbital remote sensing systems. Spectral variations due to mineralogy, vegetative cover, and condensed water are effectively mapped by the visible and near-infrared multispectral imagery, showing a wide variety of biological, meteorological, and geological phenomena. Global tectonic and volcanic processes are clearly illustrated by these images, providing a useful basis for comparative planetary geology. Differences between plant species are detected through the narrowband IR filters on Galileo, allowing regional measurements of variation in the "red edge" of chlorophyll and the depth of the 1-micrometer water band, which is diagnostic of leaf moisture content. Although evidence of life is widespread in the Galileo data set, only a single image (at approximately 2 km/pixel) shows geometrization plausibly attributable to our technical civilization. Water vapor can be uniquely imaged in the Galileo 0.73-micrometer band, permitting spectral discrimination of moist and dry clouds with otherwise similar albedo. Surface snow and ice can be readily distinguished from cloud cover by narrowband imaging within the sensitivity range of Galileo's silicon CCD camera. Ice grain size variations can be mapped using the weak H2O absorption at 1 micrometer, a technique which may find important applications in the exploration of the moons of Jupiter. The Galileo images have the potential to make unique contributions to Earth science in the areas of geological, meteorological and biological remote sensing, due to the inclusion of previously untried narrowband IR filters. The vast scale and near global coverage of the Galileo data set complements the higher-resolution data from Earth orbiting systems and may provide a valuable reference point for future studies of global change.
伽利略号航天器在其两次飞越地球期间获取了近6000张地球多光谱图像。伽利略号的图像通过四个窄带近红外滤光片提供的光谱能力，为我们的家园星球提供了独特的视角，这些滤光片原本用于观测木星大气中的甲烷，目前运行的任何地球轨道遥感系统都未采用。矿物学、植被覆盖和凝结水引起的光谱变化通过可见光和近红外多光谱图像得到有效映射，展示了各种各样的生物、气象和地质现象。这些图像清晰地展示了全球构造和火山过程，为比较行星地质学提供了有用的基础。通过伽利略号上的窄带红外滤光片可以检测到植物物种之间的差异，从而能够对叶绿素“红边”的变化以及1微米水吸收带的深度进行区域测量，该吸收带可诊断叶片含水量。虽然在伽利略号数据集中生命迹象广泛存在，但只有一张图像（分辨率约为2公里/像素）显示出可能归因于我们技术文明的几何图案。在伽利略号0.73微米波段可以对水汽进行独特成像，从而能够对反照率相似的湿云和干云进行光谱区分。在伽利略号硅电荷耦合器件相机的灵敏度范围内，通过窄带成像可以很容易地将地表雪和冰与云层覆盖区分开来。利用1微米处微弱的水吸收可以绘制冰粒大小变化图，这项技术可能在木星卫星探索中找到重要应用。由于包含了以前未尝试过的窄带红外滤光片，伽利略号图像有潜力在地质、气象和生物遥感领域为地球科学做出独特贡献。伽利略号数据集的巨大规模和近乎全球覆盖范围补充了来自地球轨道系统的高分辨率数据，并可能为未来全球变化研究提供有价值的参考点。
