PARENT SESSION
Poster Session #18: Remote Sensing and GIS.
Tuesday, August 7, 2001. Presentation from 3:30 PM to 5:00 PM. Exhibition Hall
86
Spatio-temporal dynamics of vegetation and precipitation in the Nebraska Sand Hills.
Ratcliffe, Ian1, Henebry, Geoffrey1,2, Wedin, David2, 1 2
ABSTRACT- The Nebraska Sand Hills is the largest dune field (active or stabilized) in North America, ranging across a sparsely populated region of 50,000 km2. Major land cover types (dry upland prairie, subirrigated meadows, wetlands, and lakes) vary in proportion across the Sand Hills. We sought to characterize spatial structure of the region's interannual and seasonal variation in precipitation and vegetated land cover. We relied on two standard datastreams: the AVHRR maximum NDVI biweekly composites (USGS EROS Data Center) and the daily rainfall composites from National Weather Service radars (NASA Global Hydrology Resource Center). The 1 km NDVI image data covered a period from mid-March to mid-November for 1990-2000, excluding 1994. These data were cleansed to remove scenes obviously contaminated by compositing artifacts or snow cover. Principal components analysis (PCA) of the cleansed data revealed the spatio-temporal variation in NDVI could be effectively summarized with five PCs. Eigenvectors captured periodicities in NDVI, which could be related to land cover type, asynchronies in phenology, climatic gradients, soils, and dune morphology. The 2 km daily rainfall composites were available from 1996-2000. We analyzed these data at two temporal resolutions - daily and biweekly - using PCA to reveal recurrent precipitation patterns. Correlational analyses between estimated and observed rainfall revealed some biases due primarily to data binning. However, the comprehensive spatial coverage of the radar data facilitates estimation of regional water balance.
KEY WORDS: NDVI, space-time analysis, landscape ecology, grasslands