Study of endmember spectra suggests that iron oxidation state and hydrate mineralogy are important contributory factors in the ability to map saline soil endmembers. This was tested by unmixing endmember spectra, using Spectral Feature Fitting (SFF) methods, using image data covering only the restricted spectral VISNIR range 605 nm to 1250 nm (bands 12-55). Spectral features were maximised using continuum-removal methods.   Almost identical endmember maps to those created by applying the mixture-tuned methods to full range data were created, showing that the slope of the spectral curve and the hydrate (combined) water absorption features are, by themselves, sufficient to discriminate saline soils. This further indicates that the hydrate absorption features observed are associated with evaporite minerals and not with the normal soil clay minerals.   A colour composite of saline soil classes 1, 2 and 7 obtained from Spectral Feature Fitting the 605 nm to 1250 nm part of the endmember spectra. High abundance of all three saline endmembers, as shown by the brightest areas, coincides with the areas of greatest salinity as determined by ground geophysics (described elsewhere).   CONCLUSIONS Saline soils have distinctive spectra. Spectral features in the Visible and Near Infrared (VNIR) parts of the spectrum, related to combined water in hydrated evaporite minerals, allow saline soils to be mapped by the HyMap scanner. Image endmembers can efficiently illustrate the distribution of salinity, however, they are likely to have different compositions within multi-temporal data takes. Maps of field-derived endmembers are likely to be more useful as a tool for monitoring changes in salinity. The latter may be due to seasonal and remedial measures.

Bennett B. A.,1998. Airborne remote sensing and field spectroscopy for soil salinity mapping at Pyramid Hill, Victoria. Unpublished Masters Thesis, School of Geology, UNSW. 65p

 

Boardman J. W., 1993. Automating spectral unmixing of AVIRIS data using convex geometry concepts. In Summaries of the Fourth Annual JPL Airborne Geosciences Workshop, JPL Publication 93-26, 1, 11-14

 

Boardman J. W., Kruse F. A. and Green R. O., 1995. Mapping target signatures via partial unmixing of AVIRIS data: In Summaries Fifth JPL Airborne Earth Science Workshop, JPL Publication 95-1, 1, 23-26.

 

Environment for Visualizing Images (ENVI) , Better Solutions Consulting, 1993 - 1999.

 

Green A. A., Beramn M., Switzer P. and Craig M. D., 1988. A transformation for ordering multispectral data in terms of image quality and implications for noise removal. IEEE Trans. Geosc. and Rem. Sens., 26, 1, 65-74

 

Taylor G. R., Reston M. and Cocks T., 1998. Spectral Endmembers determined from the Hymap Imaging Spectrometry. 9th Australasian Remote Sensing and Photogrammetry Conference, Sydney. Paper published in full on CD.

 

Taylor G. R., Bennett B. A., Mah A. H. and Hewson R. D., 1994. Spectral properties of salinised land and implications for interpretation of 24 channel imaging spectrometry. Proceedings of the First International Remote Sensing Conference and Exhibition, Strasbourg, France, Volume 3, 504-513.