Monitoring Drought Using Coarse-Resolution Polar-Orbiting Satellite Data - Monitoring and Predicting Agricultural Drought: A Global Study - page 63

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[63],

Line
——
-1.1
——
Norm
PgEn

[63],

Fig ure 5.4 The relationships between total wet biomass of grass canopy ( > 90 green) and (A)
the red (0.63-0.69 µ m) spectral radiance, (B) near-infrared (0.75-0.80 µ m) spectral radiance,
and (C) the normalized difference vegetation index (from Tucker, 1977).

vegetation identification. In fact, all of the slope-based VIs can be shown to
be functionally equivalent to each other (Perry and Lautenschlager, 1984).

D istance-Based Vegetation Indices

Perpendicular Vegetation Index The family of distance-based vegetation
indices were originally derived from the perpendicular vegetation index
(PVI) formulated by Richardson and Wiegand (1977). The principal ob-
jective of these VIs is to eliminate the effect of soil brightness over surfaces
of incomplete vegetation cover where a mixture of green vegetation and
soil background dominates the surface. This is particularly important in
detecting the presence of vegetation in arid, semiarid, and subhumid en-
vironments. The procedure for deriving the PVI is based on the soil line
concept, which describes the typical range of soil signatures in red/near-
infrared bispectral plots. The soil line is computed by linear regression of