热液蚀变岩类是在含矿热液作用下引起原岩化学成分和物理性质发生变化的结果,因此蚀变岩类往往与内生矿产伴生,有时其本身就是含矿体。不同蚀变矿物组合具有独特的光谱响应,但是光谱的反射和吸收特征较弱称为遥感找矿弱信息标志。应用遥感技术手段和计算机数字图象处理方法探测、识别和提取这种弱信息标志指导找矿是遥感地质工作的重要任务之一。该文介绍了利用TM多光谱数据提取含矿蚀变带的方法。实际工作证实此方法具有简单、快速、实效的特点,有一定的推广价值。

TM imagery uses 0-255 grey levels to represent different spectrum of the ground truth. In the ease of using TM data to enhance and map mineral bearing alterations, Amos (1989) and Zhao Yuanhong (1991) applied TM ratio+ PCA to enhance alterations with eliminating the influencial factor of vegetation; Crosta (1991) and loughlin (1991) used PCA+ negative+ PCA to successfully identify alterations. However, those methods have unsatisfactory results in the areas where dominanted with forestry、grass、glacial ice、loess、water bodies、and clouds. The new methodology to eliminate those environment factors which have strong spectral reflectance comparing with relative weak spectral reflectance of alterations, and which have impact on spectral signatures of the TM data in terms of differentiating alterations from surrounding rocks is developed mainly by TM data masking-PCA-supervised and unsupervised classification in the testing areas selected both in Canada and China. The results are proved vary effective.