|Hunsaker, Douglas - Doug|
|Pinter, Jr., Paul|
Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/10/2007
Publication Date: 12/20/2007
Citation: French, A.N., Hunsaker, D.J., Clarke, T.R., Fitzgerald, G.J., Luckett, W.E., Pinter, Jr., P.J. 2007. Energy balance estimation of evapotranspiration for wheat grown under variable management practices in central arizona. Transactions of the ASABE. 50(6):2059-2071 Interpretive Summary: Knowing how much water is consumed by a crop or is lost through evaporation from the soil, is important for helping farmers decide when and how much to irrigate. These processes, collectively called evapotranspiration (ET), can be estimated using remote sensing. Using high spatial resolution (0.5 m) data, a field experiment estimated ET over a wheat crop planted in Maricopa, Arizona in 2005. Plant cover and temperature were used as inputs to a simulation model that estimated ET over plots with different plant densities, irrigation schedules, and amounts of fertilizer. The modeled ET values agreed well with independent measurements of soil moisture. These positive good experimental results will help current researchers develop operational techniques that can potentially assist growers in their efforts to find more effective ways to schedule irrigation events.
Technical Abstract: Estimation and monitoring the spatial distribution of evapotranspiration (ET) over irrigated crops is becoming increasingly important for managing crop water requirements under water scarce conditions. The usual approaches for estimating ET, however, do not provide plot-specific data but instead produce spatially-averaged ET estimates. The only practical way to provide spatially-specific ET estimates is through remote sensing, which can observe ET-related surface properties such as vegetation density and surface temperature. A remote sensing approach that models ET including both of these observations involves using the surface energy balance, with water vapor transport as a key component. Using a two source energy balance model, ground control data, and sub-meter, airborne observations over a wheat irrigation experiment in Maricopa, Arizona in 2005 we showed that daily ET values could be accurately estimated over a wheat crop. Agreement with ET estimates based on soil moisture depletion observations was within 0.4 mm/d for most of the growing season, with exceptions for late-season senescent stages. These results suggest that spatially-distributed energy balance modeling can provide accurate daily ET estimates that are potentially useful to irrigation scheduling routines. They also indicate that optimal benefits from remote sensing will be achieved only when the estimates are integrated with nearly continuous observations from ground-based stations.