Estimation of surface heat flux and an index of soil moisture using adjoint-state surface energy balance

Estimates of surface heat flux and an index of the surface control over eva poration are made based on radiometric observations of ground temperature. A variational data assimilation approach is used to include surface energy balance in the estimation procedure as a physical constraint (the adjoint t echnique). This technique formulates the estimation problem as a minimizati on of ground temperature forecast misfits against observations. The surface energy balance equation is incorporated as a physical constraint. Applicat ions to the First International Satellite Land Surface Climatology Project Field Experiment (FIFE) are presented. The procedure estimates of the surfa ce control over latent heat flux match those values based on independent la tent heat flux measurements. The estimates of surface heat flux, when compa red with measurements, have a root-mean-square error of 20 W m(-2). The nee d to discriminate between soil wetness and aerodynamic contributions to the surface control over evaporation is recognized.