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Measurement options
Document code: SS1-UM-1.05
Advice on Absorption and ELADP values
Absorption
Absorption is the percentage of incident PAR that is absorbed by the leaf.
Most leaves have Absorption values in the range 0.8 - 0.9, so the default value of
0.85 will usually be appropriate.
Only adjust the Absorption value if you have good reason to, for example if you are
working with very thick, dark leaves, or very thin transparent ones.
If you set the Absorption value to 1.0, the LAI calculations will be equivalent to
simpler models that assume completely black leaves.
ELADP
ELADP is the Ellipsoidal Leaf Angle Distribution Parameter.
The ELADP is a way of characterising the horizontal or vertical tendency of leaves
in a canopy.
The canopy leaf elements are assumed to be
distributed in space in the same directions and
proportions as the surface area of an ellipsoid of
revolution, symmetrical about the vertical axis.
The Leaf Angle Distribution can then be
described by a single parameter, the ratio of the
Horizontal to Vertical axes of the Ellipsoid.
ELADP
H V
=
This is also equal to the ratio of the vertically projected area to the horizontally
projected area of the ellipsoid (or of the canopy elements).
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An ELADP of 1.0 gives a spherical Leaf Angle Distribution, where all leaf angles
are equally represented.
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A high ELADP (e.g. 1024) represents a broad flat ellipsoid, i.e. the leaf elements
are all horizontal
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A low ELADP (0.0) represents a tall thin ellipsoid, i.e. all the leaf elements are
vertical.
Most crops have ELADPs in the range 0.5 - 2.0.
Setting ELADP
The default setting of 1.0 (spherical leaf angle distribution) is a good starting point.
If you are unable to estimate the ELADP any other way, set ELADP to 1.0. You can
check how much this affects your results in the field by making several
measurements in one place within a canopy using different ELADP values, and
comparing the LAI values calculated.
V
H
