The von Mises equation was modified to describe numerically irregular distr
ibutions of leaf azimuth density. The new equation has three indexes: T (de
scribing distribution elongation), S (describing number of azimuth preferen
ces), and R (describing general canopy azimuth position). The equation was
tested on two contrasting canopies: sunflower and maize. In 1998, the diurn
al variation of leaf azimuths was measured weekly beginning 66 days after p
lanting for 5 weeks. The equation was tested again in 1999. The equation ch
aracterised the leaf azimuth densities accurately (mean absolute estimation
error of 0.05). For sunflower, R index was linearly related to sun azimuth
, and sunflower generally tracked the sun in the same way for both years be
cause they had almost equal R at a given sun azimuth. However, the azimuth
density distribution in 1999 was slightly more clumped than in 1998, and th
at sunflower canopies in 1998 would fluctuate between one to two azimuth pr
eferences, but sunflower in 1999 generally showed one azimuth preference. F
or maize, mean T,S and R for 1998 and 1999 were similar to each other These
values agreed with field observations, where maize canopies were usually e
longated, having two azimuth preferences that were perpendicular to plantin
g row direction. Logistic regression showed that these indexes were descrip
tive enough to differentiate between sunflower and maize canopies with an a
ccuracy greater than 80%. The most important index to differentiate between
canopy types was T, S, then R. (C) 2000 Elsevier Science B.V. All rights r
eserved.