HR: 1340h
AN: B43B-0271    [Abstracts]
TI: Synergistic Use of AMSR-E and MODIS Data for Understanding Land Surface Phenology: a Case Study in the Great Plains of North America
AU: * Doubková, M
EM: mdoubkova@calmit.unl.edu
AF: Marcela Doubková, Center for Advanced Land Management Information Technologies (CALMIT), 102 E Nebraska Hall, University of Nebraska-Lincoln, Lincoln, NE 68588-0517 United States
AU: Henebry, G M
EM: Geoffrey.Henebry@sdstate.edu
AF: Geoffrey M. Henebry, Geographic Information Science Center of Excellence (GIScCE), Wecota Hall, Box 506B, South Dakota State University, Brookings, SD 57007 United States
AB: Native grasslands of the Great Plains once constituted a vast biome spanning temperature and precipitation gradients and diverse edaphic conditions across the North American mid-continent. Transformations of the grasslands and their embedded wetlands to agriculture and other anthropogenic land covers over past two centuries highlight their value as a natural resource. In recent investigations into the response of native grasslands to global environmental changes, rainfall variability was offered as a key factor to explain ecosystem structure and function. In particular, changes in temporal patterns of precipitation was shown to alter the key carbon cycling processes, such as net photosynthesis and above ground productivity, and ecological patterns like community composition. To understand the impact of rainfall variability in grasslands, an understanding of soil moisture dynamics is critical. Passive microwave sensors can detect changes in moisture content at the soil surface and in vegetation canopies. Here we investigate the spatio-temporal trends and sensitivities of two Advanced Microwave Scanning Radiometer (AMSR-E) standard data products (vegetation water content and soil moisture) to (1) precipitation events, (2) growing season dry spells, and (3) land cover composition. The study area covers 1 400 000 km² and spans from southeastern Kansas to eastern Montana. AMSR-E acquisitions occur twice daily - 1:30 (descending pass) and 13:30 (ascending pass) - enabling the AMSR-E data products to respond rapidly to changes in surface conditions. The low spatial resolution of these products (25 km) calls for the synergistic use of other EOS data products with higher spatial resolution. In a previous study focused on the Nebraska Sand Hills, we found a strong correspondence between the land surface phenology captured by biweekly composites of AVHRR NDVI and the seasonal development of daily vegetation water content retrievals from AMSR-E. Here we assess the ability of MODIS (Moderate Resolution Imaging Radiometer) data products to evaluate the sensitivity of AMSR-E data products. We used MODIS data products for vegetation indices (MOD13) and land cover type (MOD12). We found significant correspondences between MODIS vegetation indices and the AMSR-E vegetation water content product in areas that were dominated by herbaceous vegetation. The sensitivities of both the vegetation water content and soil moisture products to storm events and the rapidity of drydown were modulated by land cover type, edaphic conditions, and recent weather. While these findings are preliminary, they suggest that the high temporal but low spatial resolution of canopy dynamics offered by AMSR-E data products can be complemented by the lower temporal but higher spatial resolution of MODIS vegetation indices. It is clear that the passive microwave products can provide an important window into grassland phenology.
DE: 0429 Climate dynamics (1620)
DE: 0438 Diel, seasonal, and annual cycles (4227)
DE: 0439 Ecosystems, structure and dynamics (4815)
DE: 0480 Remote sensing
SC: Biogeosciences [B]
MN: Fall Meeting 2005