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THE INFLUENCE OF VIEW GEOMETRY VARIATION IN SPECTRAL 
BEHAVIOUR OF HERBACEOUS VEGETATION IN PASTURES 
OF BRACHIARIA DECUMBENS AND BRACHIARIA BRIZANTHA 
Ademir Fernando Morelli 
Universidade do Vale do Paraiba - UNIVAP 
Depto. de Geociéncias e História 
Pca Cándido Dias Castejon, 166 
12200-000 - Sao José dos Campos - SP, Brazil 
ISPRS Commission VII / Working Group 1 
ABSTRACT 
The objective of this research was to evaluate the influence's valuation of view geometry variation in 
spectral behaviour of herbaceous vegetation and soil underlying in composition pastures for Brachiaria 
decumbens Stapf. cv. Basilik Stapf and Brachiaria brizantha Stapf. cv. Marandu. The metodology 
development involved the report analysis between the spectral reflectance and the biophysics parameters 
of herbaceous vegetation and soil. For this purpose radiometric and biophysics measurements were done 
for 25 vegetation samples nad one soil sample, in experiment areas of 1000 m2, for each species. The 
multiespectral bidirectional reflectance measurements (500 to 1100 mm) were obtained in the view 
zenith angles (0y) of 0°, 150, 300, 450 and 600 for the three sectors of azimutal plain (Ov=00, 900 and 
1800), with the solar zenith angle variation controlled for an amplitude of the 100 (0s-450 to 550) and 
the azimutal variation compensated in the acquisition method. The following vegetation parameters were 
measured: fresh and dry biomass, fresh and dry green biomass, droughtry biomass and leaf and systems; 
water content of total, green and droughtry biomass, Leaf Area Index (LAI) and percentage of canopy 
cover. The soil parameters available were color, roughness and chemistry composition. The general 
scattering behaviour was coherent with the dynamics observed in the literature and was supported by two 
principal phenomena: the "phase function" and "geometric effect 1". The major trends observed in the 
reflectance factor occurred in the azimuth in the principal plane of the sun (0s-00 and 1800), while the 
minor trends occurred in the azimuth direction perpendicular to the principal plane of the sun (Ov=900). 
For all view angles and spectral bands the minimum reflectance occurred near nadir (Ov=00) and 
increased with increasing view zenith angles for all azimuth directions. This trends is caused by the 
shading of lower canopy layers, by components in the upper lyres and by viewing different proportions of 
the layer components as the view angle changes (“effect 1"). In some cases by an active effect of "phase 
function", the reflectance minimum was shifted slightly off-nadir in the forward scattering direction 
(0s=00). This shift was maximized for occurrence of reproductive structures in the top layers of cover, 
because this structure is vertical and opaque. The major information content about vegetation cover was 
obtained in the principal plane of the sun, in the backscattering direction (02-1800), than showed better 
relationships to the vegetation parameters, because of the occurrence of "hot spot". The vegetation 
parameters of production and water content showed the best correlations, because its parameters have 
more association to the near infra-red, that exhibited the better performance than visible bands, more 
associated to LAI and fresh and dry biomass components. 
015