Estimation of vegetation aerodynamic roughness of natural regions using frontal area density determined from satellite imagery

Parameterizations of the frontal area index and canopy area index of natura l or randomly distributed plants are developed and applied to the estimatio n of local aerodynamic roughness using satellite imagery. The formulas are expressed in terms of the subpixel fractional vegetation cover and one non- dimensional geometric parameter that characterizes the plant's shape. Geome trically similar plants and Poisson distributed plant centers are assumed. An appropriate averaging technique to extend satellite pixel-scale estimate s to larger scales is provided. The parameterization is applied to the esti mation of aerodynamic roughness using satellite imagery for a 2.3 km(2) con iferous portion of the Landes Forest near Lubbon, France, during the 1986 H APEX-Mobilhy Experiment. The canopy area index is estimated first for each pixel in the scene based on previous estimates of fractional cover obtained using Landsat Thematic Mapper imagery. Next, the results are incorporated into Raupach's [Raupach, M.R., 1994. Boundary-Layer Meteorol. 71, 211-216] analytical formulas for momentum roughness and zero-plane displacement heig ht. The estimates compare reasonably well to reference values determined fr om measurements taken during the experiment and to published literature val ues. The approach offers the potential for estimating regionally variable v egetation aerodynamic roughness lengths over natural regions using satellit e imagery when there exists only limited knowledge of the vegetated surface , (C) 1999 Elsevier Science B.V, All rights reserved.