Delta SS1-UM-1.05 User Manual download pdf (Page 44)

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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).

• An ELADP of 1.0 gives a spherical Leaf Angle Distribution, where all leaf angles

are equally represented.

• A high ELADP (e.g. 1024) represents a broad flat ellipsoid, i.e. the leaf elements

are all horizontal

• 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.

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Delta SS1-UM-1.05 User Manual Page 44