Spectral data analysis and simulation tools

SFIT 2

SFIT2 is a software tool to analyze high-resolution ground-based (gb) Fourier Transform Infra Red (FTIR) spectra. SFIT2 contains all the components required for the retrieval of vertical volume mixing ratio (vmr) profiles from recorded atmospheric data sets in solar absorption mode...

 

 

The different components include: refractive atmospheric ray tracing, forward line-by-line radiative transfer model, Fourier Transform Spectrometer (FTS) instrument model, solar linelist, and the inverse (retrieval) module.

The purpose of SFIT2 is to solve the inverse problem that consists of determining the state of the atmosphere, in particular the vertical distributions of the target molecules, from the observed absorption spectra. In order to solve this so-called ill-posed problem, the SFIT2 retrievals request ad hoc covariance matrices for the uncertainties associated with the a priori vertical profiles of the target molecules and with the measurements. The retrieved profiles and total column amounts of the target species are the ones that provide the best representation of the truth, given the measurements and the a priori information with their respective uncertainties.

The retrieval algorithm in SFIT2 uses a semi-empirical implementation of the Optimal Estimation Method (OEM) of Rodgers (2000)[1] but also allows Tikhonov regularization.
SFIT2 [2] was jointly developed at the NASA Langley Research Center, the National Center for Atmospheric Research (NCAR) and the National Institute of Water and Atmosphere Research (NIWA).


Reference

[1] C. D. Rodgers, "Inverse Methods for Atmospheric Sounding: Theory and Practice", World Scientific Publishing Co. Ltd. (2000).

[2] C. P. Rinsland, et al., "Northern and southern hemisphere groundbased infrared spectroscopic measurements of tropospheric carbon monoxide and ethane", J. Geophys. Res., 103, 28197–28218 (1998).

 

ASIMUT

ASIMUT is a modular software for radiative transfer calculations in planetary atmospheres. The ASIMUT software has been developed to exploit the synergy existing between the growing number of different instruments working under different geometries...

The radiative transfer model in ASIMUT is limited to non-scattering atmospheres. In order to deal with scattering, ASIMUT has been coupled to more sophisticated RT models and this has led to the ALVL software package.

 

 

The main particularities of the ASIMUT software are:

  • The possibility to retrieve columns and/or profiles of atmospheric constituents simultaneously from different spectra, which may have been recorded by different instruments or obtained under different geometries. This allows the possibility to perform combined retrieval, e.g., of a ground based measurement and a satellite-based one probing the same air mass, or from spectra recorded by different instruments on the same platform;
  • The analytical derivation of the Jacobians;
  • The use of the Optimal Estimation method (OEM), using diagonal or full covariance matrices;
  • Its portability;
  • Its modularity, hence the ease to add future features.

Initially developed for the Earth atmosphere, its applicability has been extended to planetary atmospheres.


ALVL

ALVL (ASIMUT-LIDORT/VLIDORT) is a scientific software package primarily designed to simulate the propagation of radiation through the atmospheres of different planets in
plane-parallel (or pseudo-spherical) geometry. It is a combination of 5 state-of-the-art scientific codes responsible for modelling different aspects...

 

 

Code

Author*

Purpose (with regard to the use of a given code in ALVL)

ASIMUT
(Unix version)

A.C. Vandaele, M. De Mazière,
M. Kruglanski, N. Kumps,
V. Letocart (IT support)
BIRA-IASB, Brussels, Belgium

Calculation of molecular atmosphere parameters needed as input for LIDORT/VLIDORT, spectrum, simulation of instrument properties, OEM (Optimal Estimation Method as defined in [Rodgers, Inverse Methods for Atmospheric Sounding, Theory and Practice, 2000].

LIDORT

R. Spurr
RT Solutions, Cambridge MA, USA

Full scalar radiative transfer (including thermal emissions, no polarization).

VLIDORT

R. Spurr
RT Solutions, Cambridge MA, USA

Full vector radiative transfer (including polarization, no thermal emissions).

SPHER

M. Mishchenko
 NASA GISS, New York, USA

Calculation of aerosol atmosphere parameters needed as input for LIDORT/VLIDORT in case of spherical aerosol particles

T-MATRIX

M. Mishchenko
NASA GISS, New York, USA

Calculation of aerosol atmosphere parameters needed as input for LIDORT/VLIDORT in case of non-spherical aerosol particles.

Interface blocks

S. Kochenova,
V. Letocart (IT support)
BIRA-IASB, Brussels, Belgium

Link between the ASIMUT, LIDORT, VLIDORT, SPHER and T-MATRIX.

*Note: Several other scientists that have participated in the effort are R. Drummond (test files), T. Kerzenmacher (test files), A. Merlaud (theoretical discussions), and G. Vanhaelewyn (help with testing).


Such a combination allows one to use ALVL (1) to model:

  • solar and thermal sources of radiation;
  • satellite, plane and ground-based measurements;
  • spectrum range from UV to thermal IR;
  • atmospheric polarization;
  • absorption and scattering of radiation by atmospheric gases;
  • absorption and scattering of radiation by aerosols and clouds;
  • reflection of radiation from the surface (Lambertian and anisotropic).

and (2) to retrieve the concentrations of different atmospheric constituents (with the help of OEM).
 
ALVL has been undergoing elaborate validation/testing that is to be accomplished by September 2010. At the present time, it is also used to retrieve volcanic aerosol properties (the Eyjafjallajökull volcano in Iceland, active since 20 March 2010) from IASI data collected over the territory of Europe in April 2010. 

 

FLEXPART: Long range transport studies

FLEXPART is a free, elaborately tested, software package which calculates the Lagrangian trajectories and dispersion of a large number of particles. For more information, check here

 
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