The capability of Sentinel-2 image and FieldSpec3 for detecting lithium-containing minerals in central Iran

To date,there are very few studies about the spectroscopy of lithium-containing minerals(LCMs)in the scientific community.The main objective of this study is to investigate the capability of Sentinel-2 image and FieldSpec3 spectro-radiometer in terms of mapping five important LCMs,including spodumene,lepidolite,amblygonite,petalite,and eucryptite.Therefore,first the FieldSpec3 spectro-radiometer was used to create the spectral curves of the LCMs.Then,accurate spectral analysis and comparison of the studied LCMs were performed using The Spectral Geologist(TSG)and the Prism software.These two software can show even slight difference in absorption features of different LCMs,which can discriminate and identify these minerals.Lithium-bearing rocks show absorption features at~365,~2200,and~2350 nm and reflective features at~550-770 nm.These features are consistent with Sentinel-2 bands.Therefore,the created spectral curves were utilized for calibration of Sentinel-2 optical image to detect and map the potential zones of the rock units containing minerals mentioned above in a part of the central Iranian terrane.By using the Spectral Angle Mapper(SAM)classifier module,the potential areas were demarcated.Out of the five LCMs,petalite and spodumene showed more extensive coverage in the study area.Generally speaking,the largest concentration of those LCMs can be seen in southern and centraleastern parts of the study area.The comparison between spectral curves of reference and classified minerals confirmed the high capability of Sentinel-2 image for LCMs mapping.ASTER image classification results also confirmed the presence of the LCMs,but it cannot distinguish the LCMs type successfully.

Calibration of ASTER and ETM + Imagery Using Empirical Line Method——A Case Study of North-East of Hajjah, Yemen

This study is aimed at using the Empirical Line Method （ELM） to eliminate atmospheric effects with respect to visible and near infrared bands of advanced spaceborne thermal emission and reflection radiometer （ASTER） and enhanced thematic mapper plus （ETM＋） data. Two targets （Amran limestone as light target and quartz-biotite-sericite-graphite schists as dark target）, which were widely exposed and easy to identify in the imagery were selected. The accuracy of the atmospheric correction method was evaluated from three targets （vegetation cover, Amran limestone and Akbra shale） of the surface reflectance. Analytical spectral devices （ASD） FieldSpec3 was used to measure the spectra of target samples. ETM＋ data were less influenced by the atmospheric effect when compared to ASTER data. Normalized differences vegetation indices （NDVI） displayed good results with reflectance data when compared with digital number （DN） data because it is highly sensitive to ground truth reflectance （GTR）. Most of the differences observed before and after calibration of satellite images （ASTER and ETM＋） were absorbed in the SWlR region.