% Generated by roxygen2: do not edit by hand
% Please edit documentation in R/lai.R
\name{lai}
\alias{lai}
\title{Leaf Area Index}
\usage{
lai(ndvi, method = c("Jonckheere", "Chen"))
}
\arguments{
\item{ndvi}{NDVI in floating point standard scale range (-1 to 1)}

\item{method}{Method to use for index options c("Jonckheere", "Chen")}
}
\value{
A terra SpatRaster object with derived LAI vaues
}
\description{
Remote sensing measure of LAI (leaf area per ground-unit area)
}
\details{
This function calculates the Leaf Area Index (LAI) representing the amount of leaf area 
per unit of ground area. This is an important parameter for understanding the structure 
and function of vegetation, as it affects processes such as photosynthesis, transpiration, 
and carbon cycling. These two approaches are based on the empirical relationship between 
NDVI and LAI, which has been observed in many studies, and it is a widely used method for 
estimating LAI from remote sensing data. The formulas are derived from the fact that vegetation 
with higher LAI tends to have higher reflectance in the near-infrared (NIR) band and lower 
reflectance in the red band, resulting in higher NDVI values. But still, the exact relationship 
between NDVI and LAI can vary depending on factors such as vegetation type, canopy structure, 
and environmental conditions.
}
\examples{
\donttest{
library(terra)
lsat <- rast(system.file("/extdata/Landsat_TM5.tif", package="spatialEco"))
   plotRGB(lsat, r=3, g=2, b=1, scale=1.0, stretch="lin")
	
  ndvi <-  ( lsat[[4]] - lsat[[3]] ) / (lsat[[4]] + lsat[[3]]) 
		   
 # Using Jonckheere et al., (2004) method
 lai01 <- lai(ndvi)
   plot(lai01)

}

}
\references{
Jonckheere, I., Fleck, S., Nackaerts, K., Muys, B., Coppin, P. (2004). A comparison of two 
  methods to retrieve the leaf area index (LAI) from SPOT-4 HRVIR data. International 
  Journal of Remote Sensing, 25(21):4407–4425.
 
Chen, J. M., Liu, R., & Ju, W. (2014). A simple and effective method for estimating 
  leaf area index from Landsat imagery. Remote Sensing of Environment, 152:538–548.
}
\author{
Jeffrey S. Evans  <sage_insights@outlook.com>
}
