Abstract
With several bands covering iron-bearing mineral spectral features, Sentinel-2 has advantages for iron mapping. However, due to the inconsistent spatial resolution, the sensitivity of Sentinel-2 data to detect iron-bearing minerals may be decreased by excluding the 60 m bands and neglecting the 20 m vegetation red-edge bands. Hence, the capability of Sentinel-2 for iron-bearing minerals mapping were assessed by applying a multivariate (MV) method to pansharpen Sentinel-2 data. Firstly, the Sentinel-2 bands with spatial resolution 20 m and 60 m (except band 10) were pansharpened to 10 m. Then, extraction of iron-bearing minerals from the MV-fused image was explored in the Cuprite area, Nevada, USA. With the complete set of 12 bands with a fine spatial resolution, three band ratios (6/1, 6/8A and (6 + 7)/8A) of the fused image were proposed for the extraction of hematite + goethite, hematite + jarosite and the mixture of iron-bearing minerals, respectively. Additionally, band ratios of Sentinel-2 data for iron-bearing minerals in previous studies were modified with substitution of narrow near infrared band 8A for band 8. Results demonstrated that the capability for detection of iron-bearing minerals using Sentinel-2 data was improved by consideration of two extra bands and the unified fine spatial resolution.
Highlights
As an important data support for European Union’s Earth observation program, named the Copernicus Programme or Global Monitoring for Environment and Security (GMES), the Sentinel-2 mission was primarily designed for data enhancement of SPOT and Landsat missions
The four 10 m and six 20 m bands of Sentinel-2 imagery are used for environment monitoring [2,6,15], whereas the other three 60 m bands were primarily designed for atmospheric correction and cloud detection [14], which were eliminated in most studies
With the unified spatial resolution of Sentinel-2 MS20 and MS60 bands with MS10 bands, the iron-bearing minerals including goethite + hematite and hematite + jarosite in the Cuprite area were extracted by band ratios 6/1 and 6/8A, respectively, showing high consistency with the reference map
Summary
As an important data support for European Union’s Earth observation program, named the Copernicus Programme or Global Monitoring for Environment and Security (GMES), the Sentinel-2 mission was primarily designed for data enhancement of SPOT and Landsat missions. Sentinel-2 multispectral imagery (MSI) contains 13 spectral bands in the visible and near-infrared (VNIR), and short-wave infrared (SWIR) regions, with four bands at 10 m, six bands at 20 m and three atmospheric correction bands at 60 m spatial resolution [14]. Since the Sentinel-2 bands with 20 m spatial resolution in VNIR were originally designed for leaf area index, chlorophyll, water vapor absorption and atmospheric corrections [12], there were few studies on the potential of these bands for geological information extraction. Fused Sentinel-2 imagery with 10 m cell size is widely applied in land-cover/land-use mapping and change detection [26,27]. It is rarely employed in geological surveys. The capability of fused Sentinel-2 image for iron-bearing minerals were explored by proposing new band ratios and modified original band ratios for iron minerals
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