= Optimization of the albedo and Updated formulation for Bare soil fraction =

== New albedo scheme and parameter optimization ==

Main actors: Philippe Peylin, Vladislav Bastrikov

'''Objectives:''' 
 - Use observed satellite albedo to calibrate the current albedo scheme (MODIS albedo will be used first)
 - First change the bare soil albedo (currently a function of soil color following a color map from FAO and fixed albedo values for each color type (13))
 - Then optimize the standard coeficient for the vegetation NIR and VIS albedo to match the satellite albedo


All results are currently display under the page:

http://orchidas.lsce.ipsl.fr/dev/fit2.php


== Potential new calculation of the bare soil fraction (under vegetated areas) ==

Main actors: Nicolas Vuichard, Philippe Peylin, Catherine Ottle, Agnes Ducharne, ...


'''Problem:'''

 - Current formulation is f_bs = exp(-LAI/2) 
 - This formulation lead to a fraction of the vegetmax that is considered (treated) as bare soil being roughly 30% for a LAI=2
 - We believe it is too much and may have strong consequences (for the albedo, but also the partition transpiration / evaporation)


'''Proposed solutions:'''

 - Initially after a round table and investigation of how it is done in other models, Philippe P. proposed to use the same approach but with a coefficient different than 2 (like exp(-LAI/1.))
 - Nicolas Vuichard pointed that this is rather non physical and that we should seek for something more "physicaly based"
 - NV proposed to use the approach in the PhD of [attachment:chap2_goudriaan_1977.pdf Goudrian]; Few people need to investigate the approach so that we have a concensus on this solution. 

=> work in progress 

== Material about Radiative transfert: link between albedo and bare soil fraction for vegetetad areas == 

Radiative transfert course [attachment:chap02-nov-10-04.pdf Knyazikin][[BR]]

Radiative transfert course [attachment:rtTheoryPt1v0.doc Lewis part 1]

Radiative transfert course [attachment:rtTheoryPt2v6.doc Lewis part 2]