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# foliage height density
# Originally MacArthur & MacArthur (1961)
# Implemented after:
# Hashimoto, H., Imanishi, J., Hagiwara, A., Morimoto, Y., & Kitada, K. (2004). Estimating forest structure indices for evaluation of forest bird habitats by an airborne laser scanner. In M. Thies, B. Koch, H. Spiecker, & H. Weinacker (Eds.), Laser scanners for forest and landscape assessment: Proceedings of the ISPRS Working Group VIII/2, Freiburg, 3-6 October 2004, 254-258.
# http://www.isprs.org/proceedings/XXXVI/8-W2/HASHIMOTO.pdf
#TOFIX #@name
#@titel
#@description
#@author
fun_fhd <- function(a) {
l <- raster::nlayers(a)
a[a<=0]=1
p_i <- a/a[[l]]
r <- p_i * log(a / p_i)
sum(r[[1:(l-1)]])
}
#slightly changed for GridMetric output (gives already pi)
#TOFIX #@name
#@titel
#@description
#@author
fun_fhd_fu <- function(b) {
a <- subset(b, 1:6)
l<-raster::nlayers(a)
r<- -1 * ((a[[l]]) * log(a[[l]]))
sum(r[[1:(l-1)]])
}
# Vertical distribution ratio (VDR)
# VDR is a ratio of the distance between the canopy height return and the median height
# return. VDR = [CH-HOME]/CH.
# Forested regions are characterized by a dense canopy and sparse understory will exhibit lower VDR values
# Areas characterized by a more even distribution of biomass throughout the vertical profile will exhibit larger VDRs (closer to 1)
# Goetz, S. J., D. Steinberg, R. Dubayah, and B. Blair. 2007. Laser remote sensing of canopy habitat heterogeneity as a predictor of bird species richness in an eastern temperate forest, USA. Remote Sensing of Environment 108:254-263.
# http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.111.2979&rep=rep1&type=pdf
fun_vdr <- function(max,med) {
med[med < 0]=0
max[max < 0]=0
vdr <- (max - med) / max
vdr[is.na(vdr)]=0
vdr[is.infinite(vdr)]=0
vdr[vdr<0]=0
return(vdr)
}
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