Effective albedo of vegetated terrain at L-band

This paper derives an explicit expression for an effective albedo of vegetated terrain from the zero- and multiple-order radiative transfer model comparison. The formulation establishes a direct physical link between the effective vegetation parameterization and the theoretical description of absorption and scattering within the canopy. The paper presents an evaluation of the derived albedo for corn canopies with data taken during an experiment at Alabama A&M Winfield A. Thomas Agricultural Research Station near Huntsville, Alabama in June, 1998. The fields were observed with a truck-mounted L-band radiometer at horizontal polarization and incident angle of 15° for the period of two weeks. Ground truth data, including careful characterization of the corn size and orientation statistics, were also collected and used to simulate the effective albedo of the vegetation. It is shown that the effective albedo differs from the single-scattering albedo by definition. While the single-scattering albedo represents single-scattering properties of vegetation elements only, the effective albedo takes into account of all the processes taking place within the canopy, including multiple-scattering. The simulation results are in good agreement with the data and show that the effective albedo values increase monotonically as soil moisture increases.