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 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 Knyazikin​

Radiative transfert course Lewis part 1​

Radiative transfert course Lewis part 2​