|PAUL, GEORGE - Kansas State University|
|VARAPRASAD, P.V. - Kansas State University|
|AIKEN, ROBERT - Kansas State University|
|NEALE, CHRISTOPHER - Utah State University|
Submitted to: Journal of Hydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/22/2013
Publication Date: 12/2/2013
Citation: Paul, G., Gowda, P., Varaprasad, P., Howell, T.A., Aiken, R., Neale, C. 2013. Investigating the influence of roughness length for heat transport (zoh) on the performance of SEBAL in semi-arid irrigated, and dryland agricultural systems. Journal of Hydrology. 509:231-234.
Interpretive Summary: A remote sensing based evapotranspiration model was improved to develop accurate evapotranspiration maps for irrigation management in the Texas High Plains. Remote sensing based evapotranspiration maps have the potential to assist irrigation management at field to regional scales. In this study, we modified the SEBAL, one of the widely used remote sensing based models for its ability to estimate evapotranspiration. Modification involved incorporating a variable excess resistance, and locally developed ground heat flux sub-models into the SEBAL. Evaluation of the modified SEBAL with high resolution remote sensing data indicated significant improvement in its performance. The knowledge gained from this study is being used to improve other SEBAL-like models used in the United States and around the world.
Technical Abstract: Satellite-based thermal infrared remote sensing has greatly contributed to the development and improvement of remote sensing–based evapotranspiration (ET) mapping algorithms. Radiometric temperature (Ts) derived from thermal sensors is inherently different from the aerodynamic temperature (To) required for solving the bulk formulation of sensible heat (H) based on the Monin-Obukhov similarity posing an ill-fated problem. The scalar roughness length zoh, representing heat transport mechanism and described by the dimensionless parameter kB**1, was used to account for the discrepancy between radiometric and aerodynamic temperatures. Surface Energy Balance Algorithm for Land (SEBAL) with its indigenous approach of linearly relating dT (near-surface temperature gradient) with Ts across the imagery, maintained that this approach would absorb the impacts of differences between Ts and To. SEBAL utilized a constant kB**1 value of 2.3 in its initial version, and later switched to a constant zoh (z1) value of 0.1. In this study, we investigated the influence of this change in SEBAL by testing four approaches: (i) zoh derived from a constant kB**1 of 2.3, (ii) constant zoh (z1) = 0.1, (iii) constant zoh (z1) = 0.01, and (iv) spatially variable zoh from kB**1 parameterization. SEBAL was applied on 10 high-resolution airborne images acquired during BEAREX07-08 (Bushland Evapotranspiration and Agricultural Remote Sensing Experiment) field campaigns and validated against measurements from four large precision weighing lysimeters installed on two irrigated and two dryland fields. The spatially variable kB-1 produced statistically different and improved ET estimates compared to that with constant kB**1 and constant z1 (zoh) approaches. SEBAL performance for irrigated fields representing high ET, limited soil water deficits, and complete ground cover surfaces was markedly different from the dryland fields representing less ET, greater soil water deficits with sparser vegetation cover. A variable kB**1 value derived from a physical model incorporated into SEBAL generated good overall estimates while delivering better performance for dryland agricultural systems. Overall, this study focused on the classical problem of estimating heat transfer from two contrasting hydrological regimes i.e. irrigated and dryland agriculture and illustrated the existing need for a realistic consideration of excess resistance to heat transfer in single-source resistance modeling frameworks.