1. Running PROSPECT in forward mode

Jean-Baptiste Féret, Florian de Boissieu

2020-09-23

1 Running prospect in forward mode

1.0.1 Input variables

The function PROSPECT runs PROSPECT for individual samples and expects the following input variables.

  • N (default = 1.5)
  • CHL (default = 40.0 \(\mu g.cm^2\))
  • CAR (default = 8.0 \(\mu g.cm^2\))
  • ANT (default = 0.0 \(\mu g.cm^2\))
  • BROWN (default = 0.0 arbitrary units)
  • EWT (default = 0.01 \(g.cm^2\))
  • LMA (default = 0.008 \(g.cm^2\))
  • PROT (default = 0.0 \(g.cm^2\))
  • CBC (default = 0.0 \(g.cm^2\))
  • alpha (default = 40.0 degrees)

1.0.2 Output variables

PROSPECT returns a list containing directional-hemispherical reflectance and transmittance (reflectance and transmittance) corresponding to the input variables, and the corresponding wavelengths in the list element wvl.

1.0.3 run PROSPECT using default parameters over the full range from 400 nm to 2500 nm

1.0.4 run PROSPECT using user defined set of parameters over the full range from 400 nm to 2500 nm

Default values are set for undeclared parameters

1.0.5 run PROSPECT using user defined spectral domain

Following the same definition of the input parameters, user only has to adjust the spectral range from SpecPROSPECT. SpecPROSPECT$lambda contains the spectral bands for the different optical constants.

2 Comparison between PROSPECT-PRO and PROSPECT-D

PROSPECT-PRO is the latest official version released. However, you may not be interested in all these input biochemical constituents.

Still, we recommend using PROSPECT-PRO and selecting the constituents of interest, performances should correspond to your expectations.

2.0.0.1 PROSPECT-D

The only difference between PROSPECT-PRO and PROSPECT-D is that LMA is divided into proteins and CBC. Therefore, the default values in prospect correspond to calling PROSPECT-D, as PROT and CBC are set to 0. Keep in mind that either LMA or PROT and CBC should be set to 0. A message will be displayed if it is not the case:

Here is an example to run PROSPECT-D:

and another one with PROSPECT-PRO, which should lead to very similar leaf optics:

The resulting leaf optical properties are, indeed, very similar:

 

Fig. 1. Comparison between PROSPECT-D and PROSPECT-PRO, stoichiometry respected

 

while using proteins only instead of proteins + CBC to simulate LMA leads to different results:

 

Fig. 2. Comparison between PROSPECT-D and PROSPECT-PRO, Proteins only, no CBC

 

On the other hand, using CBC only instead of proteins + CBC to simulate LMA leads to very similar results compared to simulation with PROSPECT-D.

This is explained by the low proportion of poteins compared to CBC in he total comntribution to LMA, and the very similar specific absorption coefficient between LMA and CBC. This also highlights the challenges for the proper estimation of proteines from LOP.

 

Fig. 3. Comparison between PROSPECT-D and PROSPECT-PRO, CBC only, no Proteins

 

2.0.1 Run previous versions from PROSPECT-PRO

If you want to run previous versions of PROSPECT:

3 Computing a Look-Up-Table with prospect

Look-Up-Tables (LUT) are widely used in order to infer leaf charactristics from PROSPECT, based on minimization techniques. The function PROSPECT_LUT allows computation of a LUT directly based on a list of input parameters.

The following example produces a LUT with the function PROSPECT_LUT of prospect. Undefined parameters are set to their default value; Vectors of values are expected to be the same length.

CHL <- 100*runif(1000)
CAR <- 25*runif(1000)
ANT <- 2*runif(1000)
EWT <- 0.04*runif(1000)
LMA <- 0.02*runif(1000)
N   <- 1+2*runif(1000)
Input_PROSPECT <- data.frame('CHL'=CHL,'CAR'=CAR,'ANT'=ANT,'EWT'=EWT,'LMA'=LMA,'N'=N)
LUT <- PROSPECT_LUT(SpecPROSPECT,Input_PROSPECT)