Summary
The dependence of the albedo on illumination direction is analyzed by constructing a canopy model in which the individual leaves are planar, Lambertian reflectors. Leaf transmission is treated separately, and is assumed to be proportional to the cosine of the zenith angle of the leaf normal. Effects of shading and obscuration are formulated assuming random distribution of the leaves with respect to the viewing and illumination directions. Variants of the model with different azimuthal leaf distributions are created and discussed as explicit expressions of the viewing/illumination geometry and the canopy characteristics.
The canopy spectral single-scattering albedo factors, which are the conditional probabilities of a photon escaping from the canopy after a first reflection or a first transmission, are obtained by numerical integration over a hemisphere of the bidirectional reflectance and transmittance factors. Our analysis identifies the ratio of the projection of leaf area on the vertical plane perpendicular to the principal plane to that on a horizontal plane as the parameter that controls the dependence of the albedo on the solar zenith angle. The albedo factor due to the leaf transmittance generally increases with the zenith angle of illuminating beam more sharply than that due to the leaf reflectance.
Model variants with various azimuthal distributions are compared with measured albedo of soybeans. Second and higher order scatterings are accounted for in a simplified way. The degree to which a model variant fits the measured albedo and its change with the solar zenith angle depends both on the leaf inclination angleand the azimuthal distribution of the leaf area.
Similar content being viewed by others
References
Brakke, T. W., Eck, T. F., Deering, D. W., Otterman, J., 1988: Predicting surface albedo by inversion of simple models. Proc., Int. Radiation Symp., Lille, France. August 18–24.
Brakke, T. W., Smith, J. A., Harnden, J. M., 1989: Bidirectional scattering of light from tree leaves.Remote Sensing Environ. 29, 175–183.
Breece, H. T., Holmes, R. A., 1971: Bidirectional scattering characteristics of healthy green soybean and corn leaves in vivo.Appl. Opt.,10, 119–127.
Deering, D. W., Eck, T. F., Otterman, J., 1990: Bidirectional reflectances of selected desert surfaces and their three parameter soil characterization.Agric. and Forest Meteor. 52, 71–93.
Deering, D. W., Leone, P., 1986: Sphere scanning radiometer for rapid directional measurements of sky and ground radiance.Remote Sensing Environ.,19, 1–24.
Gates, D. M. 1980:Biophysical Ecology. New York: Springer, 611 pp.
Gerstl, S. A. W., Simmer, C. 1986: The Heiligenschein as diagnostic tool in satellite remote sensing. Los Alamos National Lab., Report LA-UR-85-4098.
Goel, N. S., Strebel, D. E., 1984: Simple Beta distribution representation of leaf orientation in vegetation canopies.Agron. J. 76, 800–802.
Goel, N. S., Thompson, R. L., 1984: Inversion of vegetation canopy models for estimating agronomic variables, V: Estimation of leaf area index and average leaf angle using measured canopy reflectances.Remote Sensing Environ. 16, 69–85.
Kimes, D. S., 1984: Modeling the directional reflectance from complete homogeneous vegetation canopies with various leaf-orientation distributions.J. Opt. Soc. Amer.,1, 725–737.
Kimes, D. S., Kirchner, J. A., 1983: Diurnal variations of vegetation canopy structure.Int. J. Remote Sensing 4, 257–271.
Middleton, E. M., Deering, D. W., Ahmad, S. P., 1987: Surface anisotropy and hemispheric reflectance for a semiarid ecosystem.Remote Sensing Environ. 23, 193–212.
Nicodemus, F. E., Richmond, J. C., Hsia, J. J., Ginsberg, I. W., Limperis, T., 1977: Geometrical considerations and nomenclature for reflectance. NBS Monograph 160. 52 pp.
Otterman, J., 1981a: Plane with protrusions as an atmospheric boundary.J. Geophys. Res. 86, 6627–6630.
Otterman, J., 1981b: Reflection from soil with sparse vegetation.Adv. Space Res. 1, 115–119.
Otterman, J., 1984: Albedo of a forest modeled as a plane with dense protrusions.J. Climate Appl. Meteor. 23, 297–307.
Otterman, J., 1985: Bidirectional and hemispheric reflectivities of a bright soil plane and a sparse dark canopy.Int. J. Remote Sensing 6, 897–902.
Otterman, J., Brakke, T. W., 1986: Penetration of sunlight into a canopy: explicit models based on vertical and horizontal leaf projections.Bound.-Layer Meteor. 36, 335–349.
Otterman, J., Staenz, K., 1985: Reflectivity contrast of forested slopes with snow-covered ground. In: Proc., 3rd Int. Coll. on Spectral Signatures of Objects in Remote Sensing, Les Arcs, France, 199–203.
Otterman, J., Strebel, D. E., Ranson, K. J., 1987: Inferring spectral reflectances of plant elements by simple inversion of bidirectional reflectance measurements.Remote Sensing Environ. 21, 215–228.
Otterman, J., Weiss, G. H., 1984: Reflection from a field of randomly located vertical protrusions.Appl. Opt. 23, 1931–1936.
Pinker, R. T., Thompson, O. E., Eck, T. F., 1980: The albedo of a tropical forest.Quart. J. Roy. Meteor. Soc. 106, 551–558.
Ranson, K. J., Biehl, L. L., Daughtry, C. S. T., 1984: Soybean canopy reflectance data set. LARS Tech. Rep. No. 071584, Purdue Univ., W. Lafayette, Ind, 46 pp.
Stewart, J. B., 1971: The albedo of a pine forest.Quart. J. Roy. Meteor. Soc. 97, 561–564.
Suits, G. H., 1972: The calculation of the directional reflectance of a vegetative canopy.Remote Sensing Environ. 2, 117–125.
Verhoef, W., 1984: Light scattering by leaf layers with application to canopy reflectance modeling: the SAIL model.Remote Sensing Environ. 16, 125–141.
Verstraete, M. M., 1987: Radiation transfer in plant canopies: transmission of direct solar radiation and the role of leaf orientation.J. Geophys. Res. 92, 10985–10995.
Author information
Authors and Affiliations
Additional information
With 6 Figures
Rights and permissions
About this article
Cite this article
Otterman, J., Brakke, T.W. Dense canopy albedo as a function of illumination direction: Dependence on structure and leaf transmittance. Theor Appl Climatol 43, 3–16 (1991). https://doi.org/10.1007/BF00865038
Received:
Revised:
Issue Date:
DOI: https://doi.org/10.1007/BF00865038