Theory

The CI-110 software calculates the solar beam transmission coefficients, or the fraction of the sky visible from beneath the plant canopy using the Gap-Fraction Inversion Procedure (Norman and Campbell, 1989).

Images of plant canopy are broken down into zenith and azimuth divisions. The fraction of sky (solar beam transmission coefficient) visible in each division is analyzed by tallying the sky portion of the image pixels.

A value between 0 and 1 is assigned; with 0 meaning no sky is visible below the plant canopy, and 1 meaning that the entire area is sky or no foliage coverage. A fraction number indicates partial foliage cover.When the divisions have been analyzed, the average solar beam transmission coefficients, hemispherical diffuse radiation transmission coefficient (the sky view factor), mean foliage inclination angles, and plant canopy extinction coefficients are computed.

The key equations involved in this process are as follow: