Soil and atmosphere exchange: simulating evapotranspiration with GLOBE measurements and NDVI

The GLOBE program is an international partnership of K-12 students, teachers, and scientists working together to study and understand the global environment. Through its suite of data collection and extensive network, GLOBE provides a valuable resource for initializing and validating SVAT models across different ecosystems. The General Purpose Simulation Model of the Atmosphere-Plant-Soil System(GAPS), a menu-driven capacitance SVAT model with multiple soil layers, was used to simulate daily water fluxes at one GLOBE site. Soil, climate, and land cover measurements made by students from Reynolds Junior and Senior High School in Greenville, PA, USA, coupled with normalized difference vegetation index(NDVI) data, derived from SPOT4 Vegetation Imagery, were used to parameterize and validate model simulations. Simulated daily soil water within the root zone for 1998 through 2001 showed a reasonable fit with soil water field measurements collected by students for that time period. A further refinement of the evapotranspiration algorithm is being investigated for improving model simulations. This revised algorithm incorporates derived phonological metrics (e.g. start and end of season, time of maximum photosynthetic activity) from temporal NDVI data and uses those metrics as input parameters for the model.