Space borne instruments measure the properties of electromagnetic waves emitted or scattered by the Earth, to understand where these waves originate from, how they interact with the environment, and how they propagate towards the sensor, mathematical models of Radiation Transfer (RT) are developed: one assume that properties about the sources of radiation and the environment are known and the model calculates the radiation field as the sensor should measure them.
In solar domain, radiation transfer models are tools to represent the scattering and absorption of radiation by scattering elements/centers. They should satisfy energy conservation. Spectral properties are depending on the geophysical medium: atmosphere, ocean, soil, or vegetation.
The semi-discrete is a 1-D radiative transfer model to simulate the transfer of solar radiation in a plant canopy and provide accurate estimates of the bidirectional reflectance of such a system as a function of the geometry of illumination and observation, as well as of the physical and structural properties of the canopy and is the one used to build the training data sets in the SeaWiFS/MERIS/OLCI/AVHRR FAPAR algorithm optimization.
This software code also simulates the transfer of solar radiation in a plant canopy and provides accurate estimates of the bidirectional reflectance of such a system as a function of the geometry of illumination and observation, as well as of the physical and structural properties of the canopy.
This model also allows the plant canopy to be better described through such variables as the number, size and orientation of the leaves, as well as the total height of the canopy. A turbid medium approach is used to represent the contribution to the total reflectance due the light scattering at orders higher than one.
The following 8 files contain all the necessary information to use this program:
The Two-stream schemes implemented in Global Climate Models (GCM) to represent the radiation transfer regimes occurring in 3-D structurally heterogeneous environments, impose the use of effective variables in order to
Remote sensing surface products, such as the albedo, the FAPAR and the Leaf Area Index (LAI), are operationally available from Space Agencies. Climate models may benefit from these products provided their 1-D radiation transfer schemes effectively represent the 3-D effects implied by the internal spatial variability of vegetation canopies, e.g., the leaf area density, at all scales and resolutions involved (say from 1 to 100 kilometers). Failing to do so leads to inherent inconsistencies between the domain-averaged reflected and absorbed fluxes, and the implied LAI.
We propose a comprehensive approach which introduces a parameterization of the internal variability of the LAI in the 1-D representation of the radiation scheme, called a domain-averaged structure factor, and provides a description of the radiant fluxes fully consistent with the LAI specified by remote sensing. We take this opportunity to revisit and update the two-stream formulations implemented in climate models to accurately estimate the fractions of radiation absorbed separately by the vegetation canopy and the underlying surface.
The input variables needed for solving this two-stream problem are as follows:
The two-stream package is build on three executables, written with the C and Fortran90 languages. They are all based on the same low-level radiation transfer routines as in [Pinty et al., 2005] but differ in their scope:
The 2stream executable is written with the C language and is built as a command-line tool which proposes a user interface with flags and options, thoroughly checks input parameters and eventually prints out the calculated fluxes. It gives access to the intermediate calculation steps (the separated radiation components) as in [Pinty et al., 2005].
It is designed as a demonstration/educational tool or as a processing tool to be included in scripts.
The Simple2stream and Simple2streamF executables are written with the C and Fortran90 languages, respectively. They are much simpler in the way the programs are written but are much less convenient to use.
They are designed to help and guide those users who would want to integrate this two-stream formulation in bigger codes (e.g. GCM) in C or Fortran.
This software code estimates the Bidirectional Reflectance Factor (BRF) of an arbitrary surface as a function of the geometry of illumination and observation, on the basis of the following three, optionally four, parameters describing the properties of that surface:
A package for the inversion of the RPV model against user supplied BRF measurements is available at 'RPV Inversion' .
This software package performs an efficient and accurate inversion of the RPV parametric model against user supplied BRF measurements. It delivers the best estimates for the model parameters along with the associated a-posteriori uncertainties on both state variables and observations. This software collection was developed in collaboration with FastOpt.
Documentation on how to install and use the software is included in the package.
Users are advised to begin with the file README which describes the installation procedure.
This software code estimates the bidirectional reflectance factor of an arbitrary surface as a function of the geometry of illumination and observation, as well as the following three parameters describing the anisotropy of that surface:
The following 5 files contain all the necessary information to use this program:
You are authorized to use this code for your research and teaching, but you must acknowledge use of this routine explicitly and refer to the paper above in any publication or work for which you used these codes.
You may distribute, free of charge, the unmodified version of these codes to colleagues involved in similar activities, provided you include all the in-line documentation. They, in turn, must agree with and abide by the same rules.
You may not sell this code to anybody, and you may not distribute it to commercial interests under any circumstances.
These tools are distributed free of charge and cannot be sold or re-sold.
It can be copied and distributed further, provided all documentation is attached and provided the original source of the software is explicitly and prominently described.
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