In this work a single TM4 band and two spectral indexes - ratio TM4/TM
3 and perpendicular vegetation index - were studied. Spectral digital
counts obtained from TM/Landsat-5 tapes were corrected for radiometric
and atmospheric effects. Wheat and bean agronomic parameters were gre
en leaf area index, percent soil cover and chlorophyll density. These
agronomic data were collected over commercial plantations on 1986 wint
er. Discussion of results were carried out on physical and physiologic
al bases. It is showed that there are good relationships between satel
lite spectral parameters and agronomic parameters for both wheat and b
ean. The possibility of estimating the vigor conditions of an agricult
ural field from orbital data was stressed. Nevertheless, in some point
of the growing season the agronomic parameters reach values so high t
hat their relationships with spectral parameters become asymptotic rat
her than linear, which would be the ideal situation. PVI, as expected,
was powerful to minimize the effect of underlying tropical soils on c
rops spectral responses.