Inferring profiles of energy fluxes within a soybean canopy using Lagrangian analysis

Two one-dimensional Lagrangian analytical dispersion models were used to estimate scalar sources, sinks and fluxes within a soybean canopy from concentration profile measurements. The two models were also used to separate soil evaporation and crop transpiration in terms of the inverse analysis. The results indicate that these two models produced similar source/sink distributions most of the time, but the values of within-canopy source distributions are dependent on the parameterizations of the turbulence statistics. The performance of these two models was similar and comparable in terms of the cumulative fluxes at the top of the canopy. The inferred above-canopy fluxes are sensitive to the parameterization of turbulence statistics, but not to the choice of model. The inferred above-canopy fluxes were in agreement with eddy covariance measurements for two turbulence schemes, while overestimated (1.8–2.6 times) when using a third turbulence scheme. Results also showed that the predicted ratio of soil evaporation to total evapotranspiration is coincident with the expected trend for different growth stages of soybean, but the value is highly dependent on the choice of turbulence statistics. The variation of daily ratio of soil evaporation to total evapotranspiration with leaf area index (LAI) from the inverse analysis is in rough agreement with that estimated from an evaporation model.