Scene Shadow Effects on Multispectral Response

The behavior of canopy reflectance and spectral bandtransformations, normalized difference (ND), and greenness (GR) dueto the amount and location of scene shadows was examined. Live balsamfir (Abies balsamea L. (Mill.)) trees were arranged in an equidistantpattern on a platform. Spectral reflectances were acquired forthree canopies (44-, 70-,and 90-pereent cover) and three backgroundtypes (grass-sod, black-,and white-painted boards) for a range of solarzenith angles. Rotating the platform produced variations in the locationof shadows cast by trees in the scene.Red and near-IR reflectance factors decreased as the amount of sceneshadows increased while ND increased with increasing scene shadows.However, when large anmounts of green vegetation were present, NDsaturated (i.e., approached an asymptote) and the observed increaseswere reduced. GR was least affected by changing shadow amounts.Spectral response variations due to shadows decreased as canopy coverincreased.A simple model was used to examine the effects of shadows in "pure"pixels of backgrounds representing vegetation, bare soil, and snow.Red and near-IR reflectance decreased and ND increased as the proprotionof shadows increased. These results suggest that green vegetationphytomass may be overestimated by ND when shadows cast byvegetation are present in a scene.

[1]  L. Biehl,et al.  Sun-View Angle Effects on Reflectance Factors of Corn Canopies , 1985 .

[2]  A. Strahler,et al.  Geometric-Optical Modeling of a Conifer Forest Canopy , 1985, IEEE Transactions on Geoscience and Remote Sensing.

[3]  Kenneth J. Ranson,et al.  Interpreting vegetation reflectance measurements as a function of solar zenith angle , 1979 .

[4]  R. Jackson,et al.  Diurnal Patterns ofWheatSpectral Reflectances , 1983 .

[5]  R. Kauth,et al.  Investigations of vegetation and soils information contained in LANDSAT Thematic Mapper and Multispectral Scanner data , 1984 .

[6]  C. Tucker.  Red and photographic infrared linear combinations for monitoring vegetation , 1979 .

[7]  R. Kauth,et al.  The tasselled cap - A graphic description of the spectral-temporal development of agricultural crops as seen by Landsat , 1976 .

[8]  K. Kriebel,et al.  Albedo of vegetated surfaces: its variability with differing irradiances , 1979 .

[9]  E. R. Stoner,et al.  Atlas of soil reflectance properties , 1979 .

[10]  J. Franklin,et al.  Coniferous Forest Classification and Inventory Using Landsat and Digital Terrain Data , 1986, IEEE Transactions on Geoscience and Remote Sensing.

[11]  D. Kimes,et al.  Irradiance measurement errors due to the assumption of a Lambertian reference panel , 1982 .

[12]  B. Holben,et al.  Red and near-infrared sensor response to off-nadiir viewing , 1984 .

[13]  Larry Biehl,et al.  Calibration Procedures For Measurement Of Reflectance Factor In Remote Sensing Field Research , 1979, Optics & Photonics.

[14]  Harold W. O'Brien,et al.  Red and near-infrared spectral reflectance of snow , 1972 .

[15]  Dwight D. Egbert,et al.  A Practical Method for Correcting Bidirectional Reflectance Variations , 1977 .

[16]  Ray D. Jackson,et al.  Diurnal Patterns of Wheat Spectral Reflectances , 1983, IEEE Transactions on Geoscience and Remote Sensing.

[17]  M. Bauer,et al.  Influence of solar illumination angle on soybean canopy reflectance. , 1982, Applied optics.

[18]  A. Cracknell,et al.  Effect of shadows cast by vertical protrusions on AVHRR data , 1985 .

[19]  Simulation of solar radiation absorption in vegetation canopies. , 1980, Applied optics.

[20]  Craig S. T. Daughtry,et al.  Sun angle, view angle, and background effects on spectral response of simulated balsam fir canopies , 1986 .