Estimation of Surface Turbulent Fluxes through Assimilation of Radiometric Surface Temperature Sequences

ABSTRACT A model of land surface energy balance is used as a constraint on the estimation of factors characterizing land surface influences on evaporation and turbulent heat transfer from sequences of radiometric surface tem- perature measurements. The surface moisture control on evaporation is captured by the dimensionless evaporative fraction (ratio of latent heat flux to the sum of the turbulent fluxes), which is nearly constant for near-peak radiation hours on days without precipitation. The dimensionless parameter capturing the turbulent transfer characteristics (bulk heat transfer coefficient) includes the impacts of both forced and free convection. The mean diurnal pattern and seasonal trends are interpreted in the context of expected surface air layer static stability variations. The approach is tested over the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE) site (Kansas) where verification data on surface fluxes are available. It is shown that sequential radiometric surface temperature data contain useful information on the partitioning of available surface energy and may even be used to infer some key characteristics of surface turbulent transfer. The land data assimilation scheme is formulated such that it does not require auxiliary data on soil texture and vegetation. Feasibility of extending the land data assimilation to use remote sensing measurements is tested by simulating the observing system sampling based on field experiment measurements. Applications with remote sensing data would allow large-scale mapping of land surface energy balance components.