@Article{MorelliFormEpip:1993:InGeVi,
               author = "Morelli, Ademir Fernando and Formaggio, Antonio Roberto and 
                         Epiphanio, Jose Carlos Neves",
                title = "Influencia da geometria de visada na reflectancia espectral de 
                         duas gramineas forrageiras",
              journal = "Revista UNIVAP",
                 year = "1993",
               volume = "1",
               number = "1",
                pages = "27--42",
                month = "set.",
             abstract = "The objective of this research was to evaluate the influence's 
                         valuation of view geometry variation in spectral behavior of 
                         herbaceous vegetation and soil, underlying in composition pastures 
                         for Brachiaria decumbens Stapf. cv. Basilisk Stapf and Brachiaria 
                         brizantha Stapf. cv. Marandu. The methodology 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 andone soil sample, in experiment areas of 1000 
                         m2, for each species. The multispectral bidirectional reflectance 
                         measurements (500 to 1100 nm)were obtained in the view zenith 
                         angles ( v)of 0 , 15 , 30 , 45 and 60 for three sectors of 
                         azimutal plain ( v=0 , 90 and 180 ), with the solar zenith angle 
                         variation controlled for an amplitude of the 10 ( s=45 to 55 ) and 
                         the solar 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 stems; water content of total, green and droughtry 
                         biomassa, Leaf Area Index (LAI)and percentage of canopy cover. The 
                         soil parameters available were color, roughness and chemistry 
                         composition. This research intent was the comprehension of 
                         physical mechanisms involved in the directional reflectance factor 
                         distribution of complete homogeneous vegetation canopies and its 
                         influences in the relation between spectral behavior and 
                         vegetation parameters. The general scattering behavior was 
                         coherent with the dinamics observed in the literature and 
                         wassupported by two principal phenomena: the {"}phase function{"} 
                         and {"}geometric effect 1{"}. The major trends observed in the 
                         reflectance factor ocurred in the azimuth in the principal plane 
                         of the sun ( s=0 and 180 ), while the minor trends ocurred in the 
                         azimuth direction perpendicular to the principal plane of the sun 
                         ( s=90 ). For all view angles and spectral bands the minimum 
                         reflectance ocurred near nadir ( v=0 ) and increased with 
                         increasing view zenith angles for all azimuth directions. This 
                         trend is caused by the shading of flower canopy layers, by 
                         components in the upper layers and by viewing different 
                         proportions of the layer components as the view angle changes 
                         ({"}effect 1{"}). In some cases by an additional effect of 
                         {"}phase function{"}, the reflectance minimum was shifted slightly 
                         off-nadir in the foward scattering direction ( s=0 ). This shift 
                         was maximized for ocurrence of reproductive structures in the top 
                         layers of cover, because this structure is vertical and opaque. 
                         The near infra-red band was less influenced by view geometry 
                         variation than in the spectral bands of visible, because in the 
                         near infra-red band the transmitance was nearly equal to the 
                         reflectance for most structural components of herbaceous 
                         vegetation, while in the visible the reflectance is major, 
                         consequentely the {"}effect 1{"} is maximized. The major 
                         information content about vegetation cover was obtained in the 
                         principal plane of the sun, in the backscattering direction ( =180 
                         ), than showed better relationships to the vegetation parameters, 
                         because of the ocurrence of {"}hot spot{"}. The vegetation 
                         parameters of prodution and water content showed the best 
                         correlations, because its parameters have more association to the 
                         near infra-red, that exbited the better performance than visible 
                         bands, more associated to LAI and fresh and dry biomass 
                         components. The {"}effect 1{"} was the dominant phenomenon with 
                         controlled the directional reflectance distributions observed, but 
                         had its effects alterated by the action of aditional phenomenon 
                         {"}phase function{"}.",
                 issn = "1517-3275",
                label = "6186",
           targetfile = "INPE 6526.pdf",
        urlaccessdate = "28 abr. 2024"
}