Submitted to: International Association of Hydrological Science
Publication Type: Proceedings
Publication Acceptance Date: 8/31/2007
Publication Date: 3/1/2008
Citation: French, A.N., Schmuggee, T.J., Ritchie, J.C., Hsu, A.Y., Jacob, F., Ogawa, K. 2008. Detecting land cover change at the Jornada Experimental Range, New Mexico with ASTER emissivities. International Union of Geodesy and Geophysics Meeting. IAHS Publ. 316, p. 27-33. Interpretive Summary: A remote sensing study was done over the USDA/ARS Jornada Experimental Range, New Mexico to determine if changes in rangeland vegetation cover could be detected using satellite-based thermal infrared data. In semi-arid regions such as Jornada the vegetation is non-green much of the year and cannot be easily detected with conventional remote sensing techniques. However, using thermal infrared images to estimate surface emissivity (a measure of thermal radiation efficiency) could help detect vegetation cover even while dormant. The technique is based on the observation that land covered with vegetation usually has a higher emissivity than land with no cover. This is likely due to differences in surface roughness. Greater roughness makes the surface a more efficient emitter and consequently increases its emissivity. The technique was applied to remote sensing data acquired between 2001 and 2003 over Jornada. Using emissivity estimates derived from the ASTER spaceborne sensor, patches of land were detected that may correspond to rangeland degradation. The patches, ~5-10 km in extent, showed significant emissivity decreases and are believed to be locations with greatly decreased vegetation cover. The outcome of this study could be important for researchers and rangeland managers who are concerned with long term land cover conditions.
Technical Abstract: Detecting land cover change over semi-arid rangeland is important for monitoring vegetation responses to drought, population expansion, and changing agricultural practices. Such change can be detected using vegetation indices, but these do not represent non-green vegetation and are dominated by seasonal changes. An alternative is to observe spatial changes in thermal emissivities, a measure that responds to soil surface composition and vegetation cover. Because soil emissivities are usually stable, temporal emissivity changes could be due to vegetation cover changes. Using ASTER thermal infrared observations, the technique is applied to observations over the Jornada Experimental Range in New Mexico between 2001 and 2003. The study showed spatially coherent regions where broadband emissivities decreased as much as 3%. These coherent regions may correspond to decreased vegetation densities, suggesting that the technique could be helpful for monitoring rangeland cover.