Imaging spectroscopy measures desertification in United States and Argentina

TitleImaging spectroscopy measures desertification in United States and Argentina
Publication TypeJournal Article
Year of Publication2001
AuthorsAsner GP, Green RO
JournalEos, Transactions, American Geophysical Union
Date Published2001
Accession NumberJRN00333
Call Number00785
Keywordsarticle, articles, desertification, biogeochemistry, desertification, grassland, desertification, organic carbon, desertification, remote sensing, desertification, shrubland, desertification, soil nutrients, desertification, vegetation, journal, journals, remote sensing, AVIRIS, remote sensing, desertification, remote sensing, ecosystem health, remote sensing, EOS, remote sensing, grassland, remote sensing, ground reflectance, remote sensing, Hyperion, remote sensing, hyperspectral imaging, remote sensing, imaging spectroscopy, remote sensing, plant biomass, remote sensing, plant communities, remote sensing, shrub cover, remote sensing, soils, remote sensing, vegetation

Remote sensing-based monitoring of land degradation and desertification requires measurements of both live and senescent vegetation extent and condition, as well as bare soil areas, over large regions. Imaging spectroscopy (hyperspectral imaging) with full solar-reflected spectral signatures is now making these measurements from airborne and space-based observations. Using recent AVIRIS data sets, studies of dryland ecosystems, land degradation, and desertification are underway in the southwestern United States and central Argentina. The goals of this effort are to improve understanding of the physical and biogeochemical impacts of human activities as well as the role of climate variability in these regions. An essential element of these studies is determination of the spatial pattern and aboveground biomass distribution of live and senescent vegetation and bare soils from imaging spectroscopy data. One of the regions studied includes the Jornada Long-term Ecological Research (LTER) site, located in southern New Mexico. Images provide the observations required for quantitative studies of land degradation in these spatially complex dryland ecosystems. (1) Observations in the visible, near-infrared, and shortwave-infrared (0.4-2.5 ìm) provide a means to identify the presence of live and senescent vegetation canopies. Properties of these canopies derived from the spectroscopic measurements include leaf area index, water content, and aboveground live and senescent biomass. (2) Spectroscopic observations allow accurate measurement of vegetation and bare soil extent at the sub-pixel scale, resulting in continuous spatial fields of these surface properties. This information opens the door for new quantitative studies of ecosystem responses to land use and climate variability dryland regions. In addition to the quantification of biomass in the transition between grassland and shrubland, imaging spectroscopy also depicts varying surface conditions that represent important biogeochemical changes occurring in the region. These studies indicate that nutrient and carbon stocks are aggregated spatially in the transition zone, more so than in the grassland areas but less to than in the shrubland systems. Thus, the spatial patterning of live vegetation and surface litter is correlated with sub-surface processing of biologically important nutrients. A second region studied is a dryland region of central Argentina, where heavy grazing has resulted in another form of desertification. Spectroscopic analysis of AVIRIS data indicates areas of land degradation characterized by patterns of vegetation change previously described in Australian rangelands.

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