Delta Electronics SS1-UM-1.05 user manual Advice on Absorption and Eladp values, Setting Eladp

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.

V

H

ELADP = HV

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.

44 • Measurement options Document code: SS1-UM-1.05