Simulation of land surface fluxes using an improved dual-source model over row crops

The classical Shuttleworth-Wallace two-layer model has a modification version proposed by Norman et al. (1995) and Kustas et al. (1999) to estimate evapotranspiration over row crop surfaces. However, the assumption of this modified model is controvertible, and more theoretical analysis and data validation seem necessary to figure out whether this model is a "layer" model or a "patch" model essentially. A field data validation of this kind was carried out in this paper and it was found that a "patch" method could provide more accurate results. A new method to improve S-W model for row crop was given at the end of this paper. This model uses "layer" method to account for the in-canopy exchanges and modified surface resistances to account for the heterogeneities of row crops. The data from the composite remote sensing experiment in Shunyi, Beijing April 2001 were used to validate this model. Surface fluxes were measured by Bowen ratio system while surface radiometric temperature; component temperatures and other parameters were also measured at different atmospheric boundary layer conditions. Results show that estimation of sensible and latent beat fluxes by the new model agree well with the observed fluxes.