National ASTER Map Ferrous iron content in MgOH/carbonate

1. Band ratio: B5/B4 Blue is low ferrous iron content in carbonate and MgOH minerals like talc and tremolite. Red is high ferrous iron content in carbonate and MgOH minerals like chlorite and actinolite.Useful for mapping: (1) un-oxidised "parent rocks" - i.e. mapping exposed parent rock materials (warm colours) in transported cover; (2) talc/tremolite (Mg-rich - cool colours) versus actinolite (Fe-rich - warm colours); (3) ferrous-bearing carbonates (warm colours) potentially associated with metasomatic "alteration"; (4) calcite/dolomite which are ferrous iron-poor (cool colours); and (5) epidote, which is ferrous iron poor (cool colours) - in combination with FeOH content product (high).

1. 波段比值：B5/B4。蓝光波段对应碳酸盐及氢氧化镁（MgOH）类矿物（如滑石(talc)、透闪石(tremolite)）中的低亚铁含量，红光波段则对应碳酸盐及氢氧化镁类矿物（如绿泥石(chlorite)、阳起石(actinolite)）中的高亚铁含量。该波段比值可应用于以下五类制图工作：
(1) 未氧化“母岩”制图：即圈定运积覆盖层中裸露的母岩物质（呈现暖色调）；
(2) 矿物类型区分：区分富镁的滑石/透闪石（冷色调）与富铁的阳起石（暖色调）；
(3) 蚀变相关矿物识别：识别可能与交代蚀变伴生的含亚铁碳酸盐（暖色调）；
(4) 低亚铁碳酸盐矿物识别：识别低亚铁的方解石/白云石（冷色调）；
(5) 结合高羟基铁（FeOH）含量特征，圈定低亚铁的绿帘石(epidote)（冷色调）。