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Title:   Author  item
                                            SANCHEZ, JUAN - UNIVERSITY OF VALEN, SPAitem
                                            Kustas, William

                                                         - *Bill*item
                                            CASELLES, VICENTE - UNIVERSITY OF VALEN, SPAitem
                                            Anderson, Martha
  Submitted to: Remote Sensing of Environment
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 10/21/2007
                                    Publication  Date: 3/18/2008
                                    Citation: Sanchez, J., Kustas, W.P., Caselles, V., Anderson, M.C. 2008. Modelling surface energy fluxes over maize using a two-source patch model and radiometric soil canopy temperature observations. Remote Sensing of Environment. 112:1130-1143.Interpretive Summary: Models estimating large scale crop water use with thermal remote sensing must account for significant differences between the soil and canopy components of the thermal pixel scene. Recent progress in separating soil and canopy temperatures from dual angle composite radiometric temperature measurements has encouraged the
development of two-source (soil and canopy) approaches to estimating soil evaporation and canopy transpiration fluxes given observations of component soil and canopy temperatures. A Simplified Two-Source Energy Balance (STSEB) model has been developed using a “patch” treatment of the surface flux sources, which does not allow interaction between the soil and vegetation canopy components. A simple algorithm to predict the net radiation
partitioning between the soil and vegetation is introduced as part of the STSEB patch modeling scheme. The feasibility of the STSEB approach under a full range in fractional vegetation cover conditions is explored using data collected over a maize (corn) crop in Beltsville Maryland, USA during the 2004 summer growing season.
Measurements of soil and canopy component temperatures as well as the effective composite temperature were collected over the course of the growing season from crop emergence to cob development. Comparison with tower evapotranspiration (ET) measurements yielded relatively small errors. A detailed sensitivity analysis of the
STSEB approach to typical uncertainties in the required inputs was also conducted indicating greatest model sensitivity to soil and canopy temperature uncertainties but this still yielded errors no greater than ~30% in ET. With algorithms proposed to infer component temperatures from bi-angular satellite observations, the STSEB model
has the capability of being applied operationally over large errors for monitoring crop water stress.
                                Technical Abstract: Models estimating surface energy fluxes over partial canopy cover with thermal remote sensing must account for significant differences between the radiometric temperatures and turbulent exchange rates associated with the soil and canopy components of the thermal pixel scene. Recent progress in separating soil and canopy temperatures from
dual angle composite radiometric temperature measurements has encouraged the development of two-source (soil and canopy) approaches to estimating surface energy fluxes given observations of component soil and canopy temperatures. A Simplified Two-Source Energy Balance (STSEB) model has been developed using a “patch”
treatment of the surface flux sources, which does not allow interaction between the soil and vegetation canopy components. A simple algorithm to predict the net radiation partitioning between the soil and vegetation is introduced as part of the STSEB patch modeling scheme. The feasibility of the STSEB approach under a full range in fractional vegetation cover conditions is explored using data collected over a maize (corn) crop in Beltsville Maryland, USA during the 2004 summer growing season. Measurements of soil and canopy component temperatures as well as the effective composite temperature were collected over the course of the growing season from crop emergence to cob development. Comparison with tower flux measurements yielded root-mean-square-difference values between 15 and 50 W m-2 for the retrieval of the net radiation, soil, sensible and latent heat fluxes. A detailed sensitivity analysis of the STSEB approach to typical uncertainties in the required inputs was also conducted indicating greatest model sensitivity to soil and canopy temperature uncertainties with relative errors reaching ~30% in latent heat flux estimates. With algorithms proposed to infer component temperatures from bi-angular satellite observations, the STSEB model has the capability of being applied operationally.


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