Satellite-borne remote sensing of trace gases (SAT)

The Karlsruhe Optimized and Precise Radiative transfer Algorithm (KOPRA)






Abstract

The Karlsruhe Optimized and Precise Radiative transfer Algorithm (KOPRA) is a FORTRAN90 computer code for atmospheric radiative transfer modelling in the mid-infrared spectral range. It has been developed as self-standing algorithm including all relevant physics from the troposphere to the thermosphere as well as the instrument specific response function of the MIPAS/ENVISAT experiment besides other more standard ones. The motivation to design a new radiative transfer code besides good existing ones and the requirements to the design given by the MIPAS/ENVISAT mission are explained in Part I of this handbook. In Part II we provide the high level physical algorithm KOPRA is based on, in order to give an overview on the physical aspects included in KOPRA. In the following Parts (III to X) the solutions and their realizations for the relevant problems within the sub-tasks of radiative transfer modelling will be presented. In particular, these are the set-up of the geophysical model and the stratification of the atmosphere, the atmospheric ray path modelling, the calculation of absorption coefficients on an optimized wavenumber grid, the treatment of line-mixing, the consideration of absorption and emission of heavy molecules and of continua caused by gaseous constituents and solid particles, and the radiative transfer integration along the line of sight including the treatment of effects caused by non-local thermodynamic equilibrium (NLTE). Each sub-task has been given an individual part of the report where the problem is described starting from the high level algorithm description and going down to the realization, coding and data structure. In each part of KOPRA, optimizations have been taken into account as long as they are not on the cost of accuracy or flexibility, in order to provide a tool suitable for the analysis of numerous data in an automated retrieval set-up. These optimizations are described wherever they appear. In Part XI, two major optimizations, namely the modelling of the Voigt function by an accelerated Humlicek algorithm, as well as the optimized evaluation of the Planck function, are described. Part XII explains the modelling of the instrumental response function in terms of (apodized) instrumental line shape and the effect of finite field of view, both for the particular MIPAS/ENVISAT design details, and for more standard-designed instruments.

The following Parts deal with various extensions and add-ons to the pure radiative transfer forward algorithm and studies of the analysis of KOPRA's performance. In Part XIII the implementation of the calculation of quasi-analytical derivatives simultaneously with the radiative transfer integration and KOPRA's interface to a retrieval algorithm is described. In Part XIV the optimised choise of user-defined accuracy parameters in terms of accuracy versus computing time is analysed. An extensive validation exercise has been performed versus the renowned and reliable RFM (Reference Forward Model) from Oxford University, which is described in Part XV. The impact of specific modelling features of KOPRA on the retrieval error has been studied which led to an a posteriori justification of the modeling choices for KOPRA. This study is documented in Part XVI. Part XVII to XIX describe the architecture of KOPRA and its installation, and give a listing of the required input files and of its modules, subroutines and variables. In the last Part, XX, the graphical user interface (GUI) kopragui is explained, which allows to set up the input file, check and plot vertical profiles of input data, start KOPRA runs and plot the output spectra.

Zusammenfassung in deutscher Sprache

Table of Contents

Part I Introduction: Motivation and Requirements, by G.P. Stiller and T. von Clarmann
Part II Analytical expressions for modeling of radiative transfer and instrumental effects in KOPRA, by S. Zorn, T. von Clarmann, G. Echle, B. Funke, F. Hase, M. Höpfner, H. Kemnitzer, M. Kuntz, and G. P. Stiller
Part III Geophysical model and atmospheric layering, by M. Höpfner
Part IV Atmospheric raypath modeling for radiative transfer algorithms, by F. Hase and M. Höpfner
Part V Absorption coefficients, line collection and frequency grid, by M. Kuntz
Part VI Line mixing, by B. Funke
Part VII Cross-sections of heavy molecules and pseudo-lines, by S. Zorn, T. von Clarmann, M. Höpfner, G. P. Stiller, N. Glatthor and A. Linden
Part VIII Parameterization of continua caused by gaseous constituents, by G. Echle and M. Höpfner
Part IX The broadband continuum implementation, by M. Höpfner and G. Echle
Part X Non-LTE and radiative transfer, by B. Funke and M. Höpfner
Part XI The Voigt profile and the Planck function, by M. Kuntz and M. Höpfner
Part XII Transformation of irradiated to measured spectral distribution due to finite spectral resolution and field of view extent of a Fourier transform spectrometer, by F. Hase
Part XIII Derivatives and interface to the retrieval, by M. Höpfner
Part XIV Optimization of model accuracy parameters, by M. Höpfner and S. Kellmann
Appendix A Parameter optimization for the line--by--line radiative transfer model KOPRA to be used in MIPAS--ENVISAT retrievals
Part XV Intercomparison of the KOPRA and the RFM radiative transfer codes, by N. Glatthor, M. Höpfner, G.P. Stiller, T. von Clarmann, A. Dudhia, G. Echle, B. Funke, and F. Hase
Part XVI Overall retrieval error budget and a posteriori justification of modeling choices, by G.P. Stiller
Part XVII KOPRA architecture, by M. Höpfner
Part XVIII KOPRA installation, by M. Höpfner
Part XIX Module, subroutine and variable listing and description, by M. Höpfner
Part XX Graphical user interface, by M. Linder

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