Submitted to: Remote Sensing of Environment
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/31/2007
Publication Date: 4/15/2008
Citation: French, A.N., Schmugge, T.J., Ritchie, J.C., Hsu, A., Jacob, F., Ogawa, K. Detecting land cover change at the Jornada Experiment Range, New Mexico, with aster emissivities. Remote Sensing of Environment 112 (2008) 1730-1748. Interpretive Summary: A three-year remote sensing study was done over the USDA/ARS Jornada Experimental Range, New Mexico to investigate long-term changes in vegetation densities. The objective was to determine if the changing patterns in rangeland vegetation could be observed from satellites using thermal infrared data. Usually the patterns can be observed using vegetation indices based on reflected red and near infrared light. But when plants are senescent or dormant, these indices do not readily distinguish the plants from background soils. On the other hand plants and soils can sometimes be distinguished, at any time of year and regardless of plant color, using a multispectral thermal emissivity technique. The technique, only feasible with a few satellite sensors such as ASTER and MODIS, revealed coherently changing vegetation patterns over Jornada between 2001 and 2003. Patches of emissivity change, approximately 5-10 km in extent, appear to correspond to decreased plant density. The causes for the changes are possibly due to different rangeland management practices. The outcome of this study is important for researchers and rangeland managers concerned with monitoring land cover degradation in arid environments.
Technical Abstract: Multispectral thermal infrared remote sensing of surface emissivities can detect and monitor long term land cover changes over arid regions. The technique is based on the association between broadband emissivity and density of sparsely covered terrains. The association exists regardless of plant color, which means that it is possible to distinguish bare soils from senescent and non-green vegetation. This capability is typically not feasible with conventional vegetation indices. The method is demonstrated and verified using ASTER remote sensing observations between 2001 and 2003 over the Jornada Experimental Range, a semi-arid site in southern New Mexico, USA. A compilation of 21 cloud-free, multispectral thermal infrared scenes revealed spatially coherent patterns of broadband emissivities decreasing at rates on the order of 3% per decade with R2 values of approximately 0.82. These patterns are interpreted as regions of decreased vegetation densities, a view supported by ground-based leaf area index transect data. The multi-year trend revealed by ASTER's 90 m resolution data are independently confirmed by 1 km data from Terra MODIS. Comparable NDVI images are dominated by short-term seasonal patterns and do not detect the long-term, spatially-coherent changes in vegetation. These results show that NDVI data can be a poor substitute for actual thermal infrared data, that multispectral thermal infrared data are particularly valuable for land cover characterization, and that routine monitoring of emissivities is achievable using remote sensing instruments such as ASTER.