Estimation of surface iron oxide abundance with suppression of grain size and topography effects
Estimation of surface iron oxide abundance with suppression of grain size and topography effects
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DOI：
10.1016/j.oregeorev.2016.12.019
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发表时间：
2017-04
影响因子：
3.3
通讯作者：
S. Noda;Y. Yamaguchi
中科院分区：
文献类型：
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作者：
S. Noda;Y. Yamaguchi
氧化铁的矿物形式，如赤铁矿、针铁矿和黄钾铁铁矿，是重要的，因为它们广泛分布在地球表面，因为它们被用作矿产勘探的指示物。含有这些矿物的岩石中的氧化铁丰度可以从反射光谱中约900 nm波长的吸收深度来估计，但这一深度也受到颗粒大小和地形等外部因素的影响。本文研究了粒度对反射光谱的影响，提出了一种利用遥感数据估算地表岩石氧化铁丰度的方法，抑制了粒度和地形的影响。在实验室测量了含有氧化铁矿物的不同粒度岩粉样品的反射光谱。虽然反射率随着颗粒尺寸的减小而增加，但铁的存在使吸收深度在900 nm左右几乎不变，与样品的化学成分无关。此外，550 nm和760 nm(斜率)处的反射率之差是颗粒尺寸的函数。MCR-900D能准确地估计氧化铁丰度，这是分别用SLOPE和连续谱去除法抑制粒度和地形的影响后，吸收中心的最大吸收深度，取原始光谱和连续谱之比。MCR-900D结果与实验室实际光谱和化学氧化铁测量数据集的相关性表明，矿物形态也需要考虑。MCR-900D的结果与被归类为含有不同形式的氧化铁矿物(赤铁矿、针铁矿和黄钾铁矿)的岩石样品显著相关。最后，将MCR-900D应用于美国内华达州铜矿遗址的AVIRIS数据集。这些结果代表了热液蚀变区内氧化铁的富集带。
Mineral forms of iron oxide, such as hematite, goethite and jarosite, are important because they are widely distributed at the Earth’s surface and because they are used as indicators for mineral exploration. Iron oxide abundance in rocks containing these minerals can be estimated from the absorption depth at wavelengths of around 900 nm in a reflectance spectrum, but this depth is also affected by extraneous factors such as grain size and topography. This paper investigated the effect of grain size on reflectance spectra and proposed a method for estimating iron oxide abundance in surface rocks by using remotely sensed data with suppression of the effects of grain size and topography. Reflectance spectra were measured in a laboratory from rock powder samples of different grain sizes containing iron oxide minerals. While the reflectance increased with decreasing grain size, the presence of ferric iron caused the absorption depth to be almost constant at around 900 nm, irrespective of the chemical composition of the sample. In addition, the difference between the reflectance at 550 nm and 760 nm (Slope) was a function of grain size. Iron oxide abundance can be estimated accurately by MCR-900D, which is the maximum absorption depth at the absorption center after the effect of grain size and topography was suppressed by Slope and the continuum-removal method, which takes the ratio between the original spectrum and its continuum, respectively. Correlation of MCR-900D results with datasets of actual spectral and chemical iron oxide laboratory measurements revealed that the mineral forms also need to be considered. MCR-900D results were significantly correlated with rock samples classified as containing different forms of iron oxide minerals (hematite, goethite and jarosite). Finally, MCR-900D was applied to an AVIRIS dataset for the Cuprite site in Nevada, USA. The results represented the enrichment zones of iron oxide within hydrothermally altered areas.