PAR LAI Calculation
This screen is used to change the way PAR data is recoded. The PAR LAI calculation is fully dependent on the user entered data and does not rely on the hemispherical image for this data output. Several factors are possible to adjust by the user: light above the canopy, leaf distribution factor and the solar zenith.
The “Light Above Canopy” should be set to the PAR intensity above the canopy at the time of the measurement. The PAR sensors of the CI-110 can be used to measure the PAR directly, or an estimate of the PAR above the canopy can be used. The light above the canopy ranges from 1 to 2000 μmol/m2 s.
The “Leaf Distribution Factor (chi)” is the distribution of leaf angles within a canopy. It ranges from 0.01 to 10. The default value for chi is 1.0. At this leaf distribution factor, the canopy angle distribution is assumed to be spherical. A vertical crop, like onions, may have a chi of less than 1 (ex: 0.7), while a strongly horizontal crop, such as strawberries, may have a chi of 3 or greater. Many plants have a range or variation for this factor, such as maize (0.7-2.5). The leaf distribution factor does not produce significant error in the LAI equation.
The “Solar Zenith” ranges from 1 to 90 degrees. The solar zenith angle is measured from directly overhead to the geometric center of the sun's disc. It is based on your current position globally and the time of day. The solar zenith angle at sunrise and sunset is 90 degrees.
