In this chapter, an assessment was carried out on aerodynamic boundary surface layer characterization, where vertical vector fluxes of scalar quantities, e.g. momentum or sensible heat, are considered constant. This approach is grounded on the Prandtl mixed layer empirical theory based on the analogy between eddies in turbulent flow and molecules in laminarLaminar boundary layer flow, allowing for flux gradient assumptions. The parallels between eddy and turbulent diffusivity coefficientsDiffusivity coefficient in turbulent and laminar molecular flows and their differences in meaning were noted here. It has been shown that this theory is not strictly applicable within the surface layer in very rough canopies such as forests since vertical fluxes in these canopies are directed in the opposite direction to the gradients. The typical vertical logarithmic profile of the average air velocities in the surface layer was evaluated under different stability conditions. The empirical treatment of topics such as mass, gradient, Richardson flow numbersRichardson number, Monin–Obukhov length, dimensionless stability functionsStability functions or discrete equations for vertical moment fluxes, sensitive and latent heat, or gases in direct or iterative form were included. This empirical base is instrumental for the assessment of natural and forced convection and heat transfer in environmental systems.