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Title: Mapping evapotranspiration with high resolution aircraft imagery over vineyards using one and two source modeling schemes

Author
item XIA, TING - Tsinghua University
item Kustas, William - Bill
item Anderson, Martha
item Alfieri, Joseph
item Gao, Feng
item McKee, Lynn
item Prueger, John
item GELI, H. - Utah State University
item NEALE, C. - University Of Nebraska
item SANCHEZ, L. - E & J Gallo Winery
item ALSINA, MIMAR - E & J Gallo Winery
item WANG, Z. - Tsinghua University

Submitted to: Hydrology and Earth System Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/1/2016
Publication Date: 4/20/2016
Citation: Xia, T., Kustas, W.P., Anderson, M.C., Alfieri, J.G., Gao, F.N., Mckee, L.G., Prueger, J.H., Geli, H., Neale, C., Sanchez, L., Alsina, M., Wang, Z. 2016. Mapping evapotranspiration with high resolution aircraft imagery over vineyards using one and two source modeling schemes. Hydrology and Earth System Sciences. 20:1523-1545.

Interpretive Summary: Detailed knowledge of spatial evapotranspiration (ET) distributions (especially in near-real time) at field or finer scale is particularly useful in precision agricultural water management. In this study, high resolution aircraft thermal infrared and multispectral shortwave data are used to map ET over vineyards in central California with the Two Source Energy Balance (TSEB) model and with a simple model called DATTUTDUT (Deriving Atmosphere Turbulent Transport Useful To Dummies Using Temperature) which uses contextual information within the image to scale between radiometric land surface temperature (LST) values representing hydrologic limits of a wet surface where ET is maximum and a non-evaporative surface where ET=0. Imagery from five days throughout the growing season is used for mapping ET at the sub-field scale. Results from the two models indicate that TSEB provides more reliable ET estimates than DATTUTDUT compared to ground-based measurements. A sensitivity analysis indicates that TSEB is more sensitive to errors in LST while study domain and spatial resolution significantly influence the ET estimation from the DATTUTDUT model. Plans are underway to develop a hybrid approach that leverages the strengths of both modeling schemes and is simple enough to be used operationally with high resolution imagery. This modeling system has potential to significantly benefiit precision agricultural water management of high-value crops grown in water limited environments where there is a frequent occurrence of drought.

Technical Abstract: Thermal and multispectral remote sensing data from low-altitude aircraft can provide high spatial resolution necessary for sub-field (= 10 m) and plant canopy (= 1 m) scale evapotranspiration (ET) monitoring. In this study, high resolution aircraft sub-meter scale thermal infrared and multispectral shortwave data are used to map ET over vineyards in central California with the Two Source Energy Balance (TSEB) model and with a simple model called DATTUTDUT (Deriving Atmosphere Turbulent Transport Useful To Dummies Using Temperature) which uses contextual information within the image to scale between radiometric land surface temperature (TR) values representing hydrologic limits of potential ET and a non-evaporative surface. Imagery from five days throughout the growing season is used for mapping ET at the sub-field scale. The performance of the two models is evaluated using tower-based energy flux measurements of sensible (H) and latent heat (LE) or ET. The comparison indicates that TSEB was able to derive reasonable ET estimates under varying conditions, likely due to the physically based treatment of the energy and the surface temperature partitioning between the soil/cover crop inter-row and vine canopy elements. On the other hand, DATTUTDUT performance was somewhat degraded presumably because the simple scaling scheme does not consider differences in the two sources (vine and inter-row) of heat and temperature contributions or the effect of surface roughness on the efficiency of heat exchange. Maps of the evaporative fraction (EF=LE/(H+LE)) from the two models had similar spatial patterns but different magnitudes in some areas within the fields on certain days. Large EF discrepancies between the models were found on two of the days (DOY 162 and 219) when there were significant differences with the tower-based ET measurements, particularly using the DATTUTDUT model. These differences in EF between the models translate to significant variations in daily water use estimates for these two days for the vineyards. Model sensitivity analysis demonstrated the high degree of sensitivity of the TSEB model to the accuracy of the TR data while the DATTUTDUT model was insensitive as is the case with contextual-based models. However, study domain and spatial resolution will significantly influence the ET estimation from the DATTUTDUT model. Future work is planned for developing a hybrid approach that leverages the strengths of both modeling schemes and is simple enough to be used operationally with high resolution imagery.