研究目的
To develop and validate a method to estimate the wavelength position of F900 from reflectance data acquired in the SWIR and which contain only the long-wave slope of the absorption feature (1002–1355 nm).
研究成果
The wavelength position of F900—an indicator of ferric iron mineralogy—can be estimated from data acquired at SWIR wavelengths (1002–1355 nm). This opens up possibilities for using a single (SWIR) sensor to acquire information on ferric iron mineralogy (using F900) and other minerals with diagnostic absorptions between 1000 and 2500 nm.
研究不足
The study was conducted under laboratory conditions with artificial light. The method's applicability under natural sunlight and field conditions is yet to be fully validated.
1:Experimental Design and Method Selection
The method based on Gaussian processes (GPs) contains a covariance function—the observation angle-dependent (OAD) covariance function. The OAD uses only information related to the shape of the spectral curve to determine the wavelength position while remaining insensitive to any variations in spectral brightness. GP estimates were compared to results from estimates made from a multiple linear regression (MLR) of wavelength position on reflectance (1002–1355 nm).
2:Sample Selection and Data Sources
Mixtures of crushed rock with various proportions of goethite were prepared. The proportion of goethite is calculated from the quantitative XRD data as wt% goethite/(wt% goethite + wt% hematite).
3:List of Experimental Equipment and Materials
FieldSpec 3, Analytical Spectral Devices, Boulder, CO, USA; ASD spectrometer, Specim, Finland imaging sensors.
4:Experimental Procedures and Operational Workflow
Two experiments were done. The first compared the performances of GPs and MLR to estimate the wavelength position from data acquired from mixtures of crushed rock by a high-resolution nonimaging field spectrometer. The second applies the GP and MLR methods to hyperspectral imagery.
5:Data Analysis Methods
GP estimates of wavelength position were converted to the proportion of goethite using coefficients from a regression of the proportion of goethite determined from X-ray diffraction (XRD) on wavelength position measured directly from spectra.
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