An assessment of AVHRR/NDVI-ecoclimatological relations in Nebraska,U.S.A.

Research designed to better define relations between 1-km multitemporal AVHRR-derived NDVI data and selected climatological parameters, soil hydrological properties and land cover characteristics is summarized. Bi-weekly maximum value composite NDVI data and concurrently measured meteorological data acquired in 1990 and 1991 for Nebraska were utilized to study relations between NDVI and accumulated growing degree days,soil temperature, precipitation and potential evapotranspiration. Temporal change in NDVI was found to be closely linked with the temperature regime. NDVI-precipitation and NDVI-potential evapotranspiration relations exhibited time lags, although the length of lag varied with land cover type, precipitation, and soil hydrologic properties. NDVI response to precipitation was stronger in natural grasslands and grassland/wet meadows than in areas of irrigated cropland and mixed crop/ grass. NDVI-climate relations were strongest where vegetation was developed on soils with low root zone available water capacity and high permeability. Relations derived by using NDVI values over 3 pixel by 3 pixel windows showed little difference from those using single 1 km pixel. This may reflect both the relatively homogeneous land cover characteristics of the study area and the effect of off-nadir viewing geometry on AVHRR data acquisition.