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SALINITY MAPPING WITH HYPERSPECTRAL IMAGERY
SPECTRAL PROPERTIES OF IMAGE-DERIVED ENDMEMBERS
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The spectra of image-derived endmembers can be extracted and used as input for subsequent unmixing operations
Saline soil endmembers have a pronounced reflectance high, or shoulder, at around 800 nm, a shallow and wide hydroxyl feature at 2200 nm and broad absorption ramps at 1450 nm and 1900 nm. Wet, saline, soils have barely distinguishable hydroxyl features at 2200nm.
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Endmember 31 has hydrate absorption features at 980nm and 1165nm that resemble those of Bassanite, 2CaSO4.H2O
Saline endmember Class 1 shows some features in common with those of Polyhalite, K2Ca2Mg(SO4)4.2H2O, notably the reflectance high at 800nm.
XRD analysis of salt scald material shows the presence of Polyhalite, Halite, Bloedite, Gypsum and Hydroglauberite, Na2Ca(SO4)2.H2O, for which no spectra is available.
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MAPPING THE IMAGE-DERIVED ENDMEMBERS
The mixture-tuned, matched filter, methods found within the image processing system ENVI, allow the user to map the abundance within each pixel of the image-derived endmembers. This system ensures that false positives are eliminated.
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Saline soil endmember 1 matches the occurrence of the field-derived salt scald endmember very well. An area of high abundance of this endmember, just north of the eastern boundary of the R&D Block, coincides with a pit in which salt precipitates had formed at the time of image acquisition.
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Class 31 accords with bare salt scalds on well drained, dry, surfaces. The hydrate absorption features of the spectra of this class resemble those of bassanite, a waterpoor polymorph of gypsum.
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