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Multiple View Zenith Angle Observations of Reflectance From Ponderosa Pine StandsReflectance factors (RF(lambda)) from dense and sparse ponderosa pine (Pinus ponderosa) stands, derived from radiance data collected in the solar principal plane by the Advanced Solid-State Array Spectro-radiometer (ASAS), were examined as a function of view zenith angle (theta(sub v)). RF(lambda) was maximized with theta(sub v) nearest the solar retrodirection, and minimized near the specular direction throughout the ASAS spectral region. The dense stand had much higher RF anisotropy (ma)dmurn RF is minimum RF) in the red region than did the sparse stand (relative differences of 5.3 vs. 2.75, respectively), as a function of theta(sub v), due to the shadow component in the canopy. Anisotropy in the near-infrared (NIR) was more similar between the two stands (2.5 in the dense stand and 2.25 in the sparse stand); the dense stand exhibited a greater hotspot effect than 20 the sparse stand in this spectral region. Two common vegetation transforms, the NIR/red ratio and the normalized difference vegetation index (NDVI), both showed a theta(sub v) dependence for the dense stand. Minimum values occurred near the retrodirection and maximum values occurred near the specular direction. Greater relative differences were noted for the NIR/red ratio (2.1) than for the NDVI (1.3). The sparse stand showed no obvious dependence on theta(sub v) for either transform, except for slightly elevated values toward the specular direction.
Document ID
20010051290
Acquisition Source
Ames Research Center
Document Type
Preprint (Draft being sent to journal)
Authors
Johnson, Lee F.
(Johnson Controls World Services Moffett Field, CA United States)
Lawless, James G.
Date Acquired
August 20, 2013
Publication Date
January 1, 1994
Subject Category
Astronomy
Funding Number(s)
PROJECT: RTOP 462-43-65-10
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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