Canopy openness calculated as in the equation from
Gonsamo2011;textualrcaiman:
\(CO = \sum_{i = 1}^{N} GF(\phi_i, \theta_i) \cdot [(cos(\theta_1) -
cos(\theta_2))/n]\),
where \(GF(\phi_i, \theta_i)\) is the gap fraction of the cell \(i\),
\(\theta_1\) and \(\theta_2\) are the minimum and maximum zenith angle of
the cell \(i\), \(n\) is the number of cells on the ring delimited by
\(\theta_1\) and \(\theta_2\), and \(N\) is the total number of cells.
When a mask is provided through the m argument, the equation is modified as
follow:
\(
\frac{
CO = \sum_{i = 1}^{N} GF(\phi_i, \theta_i) \cdot [(cos(\theta_1) -
cos(\theta_2))/n]
}{ \sum_{i = 1}^{N} (cos(\theta_1) - cos(\theta_2))/n}
\).
This allows the masking of any individual cell.