The Use of a Hybrid Evapotranspiration Model With Multiple Source Remote Sensing Data.

The use of a Hybrid Evapotranspiration Model with Multiple Source Remote Sensing Data

Hatim M. E. Geli and Christopher M. U. Neale

Department of Civil and Environmental Engineering, Utah State University, USA

Estimates of daily evapotranspiration can be provided using remote sensing methods as well as from root zone water balance approaches. With the use of thermal remote sensing and Landsat imagery estimates of ET can be obtained on the satellite overpass dates. Interpolation in between the overpass dates, in some cases, is required to provide continuous daily ET. The hybrid ET approach presented by Geli (2012) and Neale et al. (2012) couples energy and water balance models to provide such estimates. The hybrid ET approach uses the two-source energy balance (TSEB) by Norman et al. (1995) to estimate instantaneous surface energy balance fluxes (SEBF) including latent heat flux which then can be extrapolated to daily ET. The water balance approach uses the reflectance-based basal crop coefficient (Kcbrf) (Neale et al., 1989) to estimate ET in between overpass dates.

On the other hand, the TSEB can be applied using MODIS imagery which is available on 1-2 days providing a more frequent coverage of the Earth’s surface. Considering its lower spatial resolution compared to Landsat, MODIS imagery has been less favorable for the estimation of ET at field scales. This study compares estimates of SEBF and ET provided by the application of a) the hybrid ET using Landsat data and b) the TSEB model using MODIS data to examine effects of lower resolution imagery on retrievals of ET and soil moisture.

The hybrid ET approach was applied to a rainfed corn and soybean fields at the Walnut Creek watershed, Iowa. The data were collected during the SMACEX project conducted during the summer of 2002 (Kustas et al. 2005). Different measurement datasets including weather and surface energy balance fluxes were provided using eddy covariance (EC) systems distributed around the area in different fields. Soil moisture measurements were also provided at multiple depths for the top 30 cm of the root zone.  SEBF, ET and soil moisture content estimates from both approaches were compared with ground-based measurements.

References

Norman, J. M., Kustas, W. P., & Humes, K. S. (1995). A two-source approach for estimating soil and vegetation energy fluxes in observations of directional radiometric surface temperature. Agricultural and Forest Meteorology, 77, 263293.

Geli, Hatim M. E. (2012). Modeling spatial surface energy fluxes of agricultural and riparian vegetation using remote sensing, Ph. D. dissertation, Department of Civil and Environmental Engineering, Utah State University.

Neale, C. M. U., Geli, H. M. E, Kustas, W. P., Alfieri , J. G., Gowda, P. H., Evett S. R., Prueger, J. H., Hipps, L. E., Dulaney, W. P., Chávez, J. L., French, A. N., & Howell, T. A. (2012). Soil Water Content Estimation using a Remote Sensing Based Hybrid Evapotranspiration Modeling Approach. Advances in Water Resources,50:152-161

Neale, C. M. U., W.C. Bausch and D.F. Heermann. 1989.  Development of reflectance based crop coefficients for corn.  Transactions of the ASAE,Vol. 32(6):1891-1899

Kustas, W. P., Hatfield, J. L., and Prueger, J. H. (2005). The Soil Moisture–Atmosphere Coupling Experiment (SMACEX): Background, hydrometeorological conditions, and preliminary findings. J. Hydrometeor., 6, 791–804.