Phase: RAMI4PILPS
The Joint Research Centre Two-stream Inversion Package (JRCTIP) [Pinty et al., 2007, 2008] is a computer efficient software package allowing to assimilate remote sensing flux products into a two-stream radiation transfer scheme suitable for climate models.
This package implements the adjoint and Hessian codes, generated using automatic differentiation techniques [Voβbeck et al., 2008], of a cost function balancing (1) the deviation from the a priori knowledge on the model parameter values and (2) the misfit between the observed remote sensing fluxes and the two-stream model simulations.
The individual weights of these contributions are specified notably via covariance matrices of the uncertainties in the prior knowledge on the JRC2S model parameters [Pinty et al., 2006] and the measurements.
The proposed procedure delivers a Gaussian approximation of the PDFs of the retrieved model parameter values.
The posterior covariance matrix is further exploited to evaluate, in turn, the posterior probability density functions of the radiant fluxes, e.g., scattered, transmitted and absorbed that are simulated by the two-stream model, including those that are not measured, e.g., the fraction of radiation absorbed in the ground.
The JRCTIP solutions can eventually be computed offline for selected sets of prior conditions and stored in look-up tables [Clerici et al., 2010].
In the context of RAMI4PILPS the inversion is performed on the basis of the eight available top-of-canopy albedos (four illumination conditions, two spectral bands), for the type of vegetation (SHB or OFC), LAI and background albedos specified in the RAMI4PILPS experiment name.
The JRCTIP took about 0.05 s per inversion on a workstation with the Linux Suse 11.1 operating system (Kernel 2.6.27.19-3.2-default) having 3.9 Gb RAM and a 2.5 GHz processor.
The code is written in C.
