Abstract

Directional reflectance factors that span the entire exitance hemisphere were measured for vegetation canopies and bare soils with different geometric structures. Two spectral bands were used—NOAA 6/7 AVHRR bands 1 (0.58–0.68 μm) and 2 (0.73–1.1 μm). Geometric measurements of leaf orientation distributions were taken when possible, and other structural and agronomic measurements were collected. For each cover type, these data were taken several different times on a clear day. Polar coordinate system plots of directional reflectance factors, along with 3-D computer graphic plots of scattered flux, were created. These field data were used in conjunction with literature data to study the dynamics of the directional reflectance factor distribution as a function of the geometric structure of the scene, solar zenith angle, and optical properties of the leaves and soil. Physical mechanisms causing the observed dynamics were proposed and were supported by a number of field and modeling studies. For complete homogeneous vegetation canopies, the major trend observed at all sun angles and spectral bands was a minimum reflectance near nadir and increasing reflectance with increasing off-nadir view angle for all azimuth directions. This trend is well known in the experimental and theoretical literature and is caused by the shading of lower canopy layers by components in the upper layers and by viewing different proportions of the layer components as the sensor view angle changes. In some cases the reflectance minimum was shifted slightly off-nadir in the foward scattering direction. The reflectance distributions tended to be azimuthally symmetric because the leaf transmittance was nearly equal to the leaf reflectance for most wavelengths. For sparse homogeneous canopies the anisotropic scattering properties of the soil significantly influenced the observed directional reflectance in the visible band. Soils have strong backscattering characteristics which can dominate the observed reflectance distribution for sparse canopies and small solar zenith angles. This knowledge is important in interpreting aircraft and satellite data, where the scan angle varies widely and can have different orientations with respect to the sun. Finally, the measured data and knowledge of the mechanics of the observed dynamics of the data can provide rigorous validation and verification tests for theoretical radiative transfer models.

© 1983 Optical Society of America

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References

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  1. D. S. Kimes, J. A. Smith, K. J. Ranson, Photogramm. Eng. Remote Sensing 46, 1563 (1980).
  2. J. A. Kirchner, D. S. Kimes, J. E. McMurtrey, Appl. Opt. 21, 3766 (1982).
    [CrossRef] [PubMed]
  3. C. J. Tucker, C. Vanpraet, E. Boerwinkle, A. Gaston, Remote Sensing Environ. (1982), in press.
  4. J. A. Kirchner, C. C. Schnetzler, Int. J. Remote Sensing 2, 253 (1981).
    [CrossRef]
  5. D. S. Kimes, J. A. Kirchner, Appl. Opt. 21, 4119 (1982).
    [CrossRef] [PubMed]
  6. D. S. Kimes, J. A. Kirchner, Remote Sensing Environ. 12, 141 (1982).
    [CrossRef]
  7. J. V. Dave, Sol. Energy 21, 361 (1978).
    [CrossRef]
  8. H. Christiansen, M. Stephenson, movie, BYU Training Manual, Civil Engineering (Brigham Young U., Provo, Utah, 1982).
  9. D. S. Kimes, J. A. Kirchner, Int. J. Remote Sensing (1982); accepted.
  10. K. L. Coulson, Appl. Opt. 5, 905 (1966).
    [CrossRef] [PubMed]
  11. F. D. Eaton, I. Dirmhirn, Appl. Opt. 18, 994 (1979).
    [CrossRef] [PubMed]
  12. D. D. Egbert, F. T. Ulaby, Photogramm. Eng. 38, 556 (1972).
  13. K. T. Kriebel, Appl. Opt. 17, 253 (1978).
    [CrossRef] [PubMed]
  14. K. J. Ranson, V. C. Vanderbilt, L. L. Biehl, B. F. Robinson, M. E. Bauer, “Soybean Canopy Reflectance as a Function of View and Illumination Geometry,” in Proceedings, Fifteenth International Symposium on Remote Sensing of Environment (Environmental Research Institute of Michigan, Ann Arbor, 1981).
  15. R. E. Oliver, J. A. Smith, “A Stochastic Canopy Model of Diurnal Reflectance,” Final Report, U.S. Army Research Office, Durham, N.C., DAH C04-74-60001 (1974). 105 pp.; T. Nilson. Agric. Meteorol. 8, 25 (1971).
    [CrossRef]
  16. J. A. Smith, K. J. Ranson, “Bidirectional Reflectance Studies Literature Review,” NASA/GSFC, prepared by ORI, Inc., 1400 Spring St., Silver Spring, Md. 20910 (1979).
  17. G. H. Suits, Remote Sensing Environ. 2, 175 (1972).
    [CrossRef]
  18. V. V. Salomonson, W. E. Marlatt, Remote Sensing Environ. 2, 1 (1971).
    [CrossRef]
  19. D. S. Kimes, W. W. Newcomb, J. B. Schutt, P. J. Pinter, R. D. Jackson, Int. J. Remote Sensing submitted.

1982 (4)

J. A. Kirchner, D. S. Kimes, J. E. McMurtrey, Appl. Opt. 21, 3766 (1982).
[CrossRef] [PubMed]

D. S. Kimes, J. A. Kirchner, Appl. Opt. 21, 4119 (1982).
[CrossRef] [PubMed]

D. S. Kimes, J. A. Kirchner, Remote Sensing Environ. 12, 141 (1982).
[CrossRef]

D. S. Kimes, J. A. Kirchner, Int. J. Remote Sensing (1982); accepted.

1981 (1)

J. A. Kirchner, C. C. Schnetzler, Int. J. Remote Sensing 2, 253 (1981).
[CrossRef]

1980 (1)

D. S. Kimes, J. A. Smith, K. J. Ranson, Photogramm. Eng. Remote Sensing 46, 1563 (1980).

1979 (1)

1978 (2)

1972 (2)

G. H. Suits, Remote Sensing Environ. 2, 175 (1972).
[CrossRef]

D. D. Egbert, F. T. Ulaby, Photogramm. Eng. 38, 556 (1972).

1971 (1)

V. V. Salomonson, W. E. Marlatt, Remote Sensing Environ. 2, 1 (1971).
[CrossRef]

1966 (1)

Bauer, M. E.

K. J. Ranson, V. C. Vanderbilt, L. L. Biehl, B. F. Robinson, M. E. Bauer, “Soybean Canopy Reflectance as a Function of View and Illumination Geometry,” in Proceedings, Fifteenth International Symposium on Remote Sensing of Environment (Environmental Research Institute of Michigan, Ann Arbor, 1981).

Biehl, L. L.

K. J. Ranson, V. C. Vanderbilt, L. L. Biehl, B. F. Robinson, M. E. Bauer, “Soybean Canopy Reflectance as a Function of View and Illumination Geometry,” in Proceedings, Fifteenth International Symposium on Remote Sensing of Environment (Environmental Research Institute of Michigan, Ann Arbor, 1981).

Boerwinkle, E.

C. J. Tucker, C. Vanpraet, E. Boerwinkle, A. Gaston, Remote Sensing Environ. (1982), in press.

Christiansen, H.

H. Christiansen, M. Stephenson, movie, BYU Training Manual, Civil Engineering (Brigham Young U., Provo, Utah, 1982).

Coulson, K. L.

Dave, J. V.

J. V. Dave, Sol. Energy 21, 361 (1978).
[CrossRef]

Dirmhirn, I.

Eaton, F. D.

Egbert, D. D.

D. D. Egbert, F. T. Ulaby, Photogramm. Eng. 38, 556 (1972).

Gaston, A.

C. J. Tucker, C. Vanpraet, E. Boerwinkle, A. Gaston, Remote Sensing Environ. (1982), in press.

Jackson, R. D.

D. S. Kimes, W. W. Newcomb, J. B. Schutt, P. J. Pinter, R. D. Jackson, Int. J. Remote Sensing submitted.

Kimes, D. S.

J. A. Kirchner, D. S. Kimes, J. E. McMurtrey, Appl. Opt. 21, 3766 (1982).
[CrossRef] [PubMed]

D. S. Kimes, J. A. Kirchner, Remote Sensing Environ. 12, 141 (1982).
[CrossRef]

D. S. Kimes, J. A. Kirchner, Int. J. Remote Sensing (1982); accepted.

D. S. Kimes, J. A. Kirchner, Appl. Opt. 21, 4119 (1982).
[CrossRef] [PubMed]

D. S. Kimes, J. A. Smith, K. J. Ranson, Photogramm. Eng. Remote Sensing 46, 1563 (1980).

D. S. Kimes, W. W. Newcomb, J. B. Schutt, P. J. Pinter, R. D. Jackson, Int. J. Remote Sensing submitted.

Kirchner, J. A.

J. A. Kirchner, D. S. Kimes, J. E. McMurtrey, Appl. Opt. 21, 3766 (1982).
[CrossRef] [PubMed]

D. S. Kimes, J. A. Kirchner, Remote Sensing Environ. 12, 141 (1982).
[CrossRef]

D. S. Kimes, J. A. Kirchner, Appl. Opt. 21, 4119 (1982).
[CrossRef] [PubMed]

D. S. Kimes, J. A. Kirchner, Int. J. Remote Sensing (1982); accepted.

J. A. Kirchner, C. C. Schnetzler, Int. J. Remote Sensing 2, 253 (1981).
[CrossRef]

Kriebel, K. T.

Marlatt, W. E.

V. V. Salomonson, W. E. Marlatt, Remote Sensing Environ. 2, 1 (1971).
[CrossRef]

McMurtrey, J. E.

Newcomb, W. W.

D. S. Kimes, W. W. Newcomb, J. B. Schutt, P. J. Pinter, R. D. Jackson, Int. J. Remote Sensing submitted.

Oliver, R. E.

R. E. Oliver, J. A. Smith, “A Stochastic Canopy Model of Diurnal Reflectance,” Final Report, U.S. Army Research Office, Durham, N.C., DAH C04-74-60001 (1974). 105 pp.; T. Nilson. Agric. Meteorol. 8, 25 (1971).
[CrossRef]

Pinter, P. J.

D. S. Kimes, W. W. Newcomb, J. B. Schutt, P. J. Pinter, R. D. Jackson, Int. J. Remote Sensing submitted.

Ranson, K. J.

D. S. Kimes, J. A. Smith, K. J. Ranson, Photogramm. Eng. Remote Sensing 46, 1563 (1980).

J. A. Smith, K. J. Ranson, “Bidirectional Reflectance Studies Literature Review,” NASA/GSFC, prepared by ORI, Inc., 1400 Spring St., Silver Spring, Md. 20910 (1979).

K. J. Ranson, V. C. Vanderbilt, L. L. Biehl, B. F. Robinson, M. E. Bauer, “Soybean Canopy Reflectance as a Function of View and Illumination Geometry,” in Proceedings, Fifteenth International Symposium on Remote Sensing of Environment (Environmental Research Institute of Michigan, Ann Arbor, 1981).

Robinson, B. F.

K. J. Ranson, V. C. Vanderbilt, L. L. Biehl, B. F. Robinson, M. E. Bauer, “Soybean Canopy Reflectance as a Function of View and Illumination Geometry,” in Proceedings, Fifteenth International Symposium on Remote Sensing of Environment (Environmental Research Institute of Michigan, Ann Arbor, 1981).

Salomonson, V. V.

V. V. Salomonson, W. E. Marlatt, Remote Sensing Environ. 2, 1 (1971).
[CrossRef]

Schnetzler, C. C.

J. A. Kirchner, C. C. Schnetzler, Int. J. Remote Sensing 2, 253 (1981).
[CrossRef]

Schutt, J. B.

D. S. Kimes, W. W. Newcomb, J. B. Schutt, P. J. Pinter, R. D. Jackson, Int. J. Remote Sensing submitted.

Smith, J. A.

D. S. Kimes, J. A. Smith, K. J. Ranson, Photogramm. Eng. Remote Sensing 46, 1563 (1980).

J. A. Smith, K. J. Ranson, “Bidirectional Reflectance Studies Literature Review,” NASA/GSFC, prepared by ORI, Inc., 1400 Spring St., Silver Spring, Md. 20910 (1979).

R. E. Oliver, J. A. Smith, “A Stochastic Canopy Model of Diurnal Reflectance,” Final Report, U.S. Army Research Office, Durham, N.C., DAH C04-74-60001 (1974). 105 pp.; T. Nilson. Agric. Meteorol. 8, 25 (1971).
[CrossRef]

Stephenson, M.

H. Christiansen, M. Stephenson, movie, BYU Training Manual, Civil Engineering (Brigham Young U., Provo, Utah, 1982).

Suits, G. H.

G. H. Suits, Remote Sensing Environ. 2, 175 (1972).
[CrossRef]

Tucker, C. J.

C. J. Tucker, C. Vanpraet, E. Boerwinkle, A. Gaston, Remote Sensing Environ. (1982), in press.

Ulaby, F. T.

D. D. Egbert, F. T. Ulaby, Photogramm. Eng. 38, 556 (1972).

Vanderbilt, V. C.

K. J. Ranson, V. C. Vanderbilt, L. L. Biehl, B. F. Robinson, M. E. Bauer, “Soybean Canopy Reflectance as a Function of View and Illumination Geometry,” in Proceedings, Fifteenth International Symposium on Remote Sensing of Environment (Environmental Research Institute of Michigan, Ann Arbor, 1981).

Vanpraet, C.

C. J. Tucker, C. Vanpraet, E. Boerwinkle, A. Gaston, Remote Sensing Environ. (1982), in press.

Appl. Opt. (5)

Int. J. Remote Sensing (2)

J. A. Kirchner, C. C. Schnetzler, Int. J. Remote Sensing 2, 253 (1981).
[CrossRef]

D. S. Kimes, J. A. Kirchner, Int. J. Remote Sensing (1982); accepted.

Photogramm. Eng. (1)

D. D. Egbert, F. T. Ulaby, Photogramm. Eng. 38, 556 (1972).

Photogramm. Eng. Remote Sensing (1)

D. S. Kimes, J. A. Smith, K. J. Ranson, Photogramm. Eng. Remote Sensing 46, 1563 (1980).

Remote Sensing Environ. (3)

G. H. Suits, Remote Sensing Environ. 2, 175 (1972).
[CrossRef]

V. V. Salomonson, W. E. Marlatt, Remote Sensing Environ. 2, 1 (1971).
[CrossRef]

D. S. Kimes, J. A. Kirchner, Remote Sensing Environ. 12, 141 (1982).
[CrossRef]

Sol. Energy (1)

J. V. Dave, Sol. Energy 21, 361 (1978).
[CrossRef]

Other (6)

H. Christiansen, M. Stephenson, movie, BYU Training Manual, Civil Engineering (Brigham Young U., Provo, Utah, 1982).

K. J. Ranson, V. C. Vanderbilt, L. L. Biehl, B. F. Robinson, M. E. Bauer, “Soybean Canopy Reflectance as a Function of View and Illumination Geometry,” in Proceedings, Fifteenth International Symposium on Remote Sensing of Environment (Environmental Research Institute of Michigan, Ann Arbor, 1981).

R. E. Oliver, J. A. Smith, “A Stochastic Canopy Model of Diurnal Reflectance,” Final Report, U.S. Army Research Office, Durham, N.C., DAH C04-74-60001 (1974). 105 pp.; T. Nilson. Agric. Meteorol. 8, 25 (1971).
[CrossRef]

J. A. Smith, K. J. Ranson, “Bidirectional Reflectance Studies Literature Review,” NASA/GSFC, prepared by ORI, Inc., 1400 Spring St., Silver Spring, Md. 20910 (1979).

D. S. Kimes, W. W. Newcomb, J. B. Schutt, P. J. Pinter, R. D. Jackson, Int. J. Remote Sensing submitted.

C. J. Tucker, C. Vanpraet, E. Boerwinkle, A. Gaston, Remote Sensing Environ. (1982), in press.

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Figures (18)

Fig. 1
Fig. 1

(a) Coordinate system defining solar and sensor angles and (b) polar plot showing scheme for plotting directional reflectance factors. The solar azimuth is always 180°. The sensors azimuth and off-nadir angles are shown as ϕ and θ, respectively. A sensor with a 0° azimuth looks into the sun. Thus, an azimuth of 0 and 180° represents forward scattering and backscattering, respectively. The spectral directional reflectance factors were plotted in a polar plot, where the distance from the origin represents the off-nadir view angle of the sensor and the angle from ϕ = 0° represents the sensor’s azimuth. The points show the directional measurements plotted. Lines of equal reflectance were contoured as presented in Fig. 3.

Fig. 2
Fig. 2

Three-dimensional plots of a directional reflectance factor distribution of a Lambertian surface with directional intervals as used in this study. The coordinate system used is presented in Fig. 1. The length of any vector as measured from the origin to the surface of the distribution represents the relative magnitude of reflectance factor in the direction of that vector. The three plots are different views: (A) A horizontal view of the X-Z plane, where the X axis is the 0° azimuth, (B) a 45° rotation of view A about the X axis, and (c) a cross section of the principal plane of the sun, which is the X-Z plane. Note that, in the context of the study, an off-nadir view angle of 90° was not measured; thus in all 3-D plots the first data point occurs at 75° off nadir.

Fig. 3
Fig. 3

Polar plots of the directional reflectance (%) in the visible band for the grass lawn. The polar coordinate system is described in Fig. 1. Solar position is shown as a small starred circle on each plot, and standard time is also indicated.

Fig. 4
Fig. 4

Three-dimensional plots of the directional reflectance in the visible band for the grass lawn at 0645 (EST). The different views are described in Fig. 2.

Fig. 5
Fig. 5

Polar plots of the directional reflectance (%) in the visible band for the soybeans. Symbols follow Fig. 3.

Fig. 6
Fig. 6

Effects of sun and view angles on dirfectional reflectance factors of complete vegetation canopies. Shading shows the relative degree that the components of various layers intercept and scatter solar flux. Dark shading is low interception and scattering, and light shading is high. The gradiate of interception and scattering as a function of canopy layers is greatest when the sun is near the horizon. In general, for all homogeneous, complete canopies and for all sun angles, the directional reflectance factor increases as the off-nadir view angle increases for any azimuth view direction. This phenomenon is referred to as Effect 1 in the text. It is caused by the shading of lower canopy layers by the components in the upper layers and by viewing different proportions of the layer components as the sensor view angle changes.

Figure 7
Figure 7

Forward scattering and backscattering of soil and vegetation. Soil generally exhibits strong backscatter and weak forward scatter because of the vertical components and opacity of the components. In contrast, complete vegetation canopies do not exhibit these extreme azimuthal variations because of the transmittance and reflectance of the components (leaves) are relatively equal.

Figure 8
Figure 8

Polar plots of the directional reflectance (%) in the visible band for the corn. Symbols follow Fig. 3.

Figure 9
Figure 9

Polar plots of the directional reflectance (%) in the visible band for the orchard grass. Symbols follow Fig. 3.

Figure 10
Figure 10

Three-dimensional plots of the directional reflectance in the visible band for the orchard grass at 0735 (EST). Symbols follow Fig. 2.

Figure 11
Figure 11

Three-dimensional reflectance in the visible band for the orchard grass at 1002 (EST). Symbols follow Fig. 2.

Figure 12
Figure 12

Polar plots of the directional reflectance (%) in the visible band for the bare soil. Symbols follow Fig. 3.

Figure 13
Figure 13

Polar plots of directional reflectance (%) in the IR band for the grass lawn. Symbols follow Fig. 3.

Figure 14
Figure 14

Polar plots of directional reflectance (%) in the IR band for the soybeans. Symbols follow Fig. 3.

Figure 15
Figure 15

Polar plots of directional reflectance (%) in the IR band for the corn. Symbols follow Fig. 3.

Figure 16
Figure 16

Polar plots of directional reflectance (%) in the IR band for the orchard grass. Symbols follow Fig. 3.

Figure 17
Figure 17

Polar plots of directional reflectance (%) in the IR band for the bare soil. Symbols follow Fig. 3.

Figure 18
Figure 18

Leaf inclination–azimuth angle distribution of the corn and soybean canopies. Standard time of measurements is indicated.

Tables (2)

Tables Icon

Table I Date, Standard Time, and Solar Zenith Angle of Directional Radiometric Measurements of Surface Types

Tables Icon

Table II Agronomic Characteristics of Vegetation Canopies; Typical Values of the Hemispherical Reflectance of the Leaves and Nadir Reflectance Factor of Soil are Shown for the Visible and IR Bands

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