Inversion Coupled with Imager (ICI)
Note: Prior to 2004 the ICI package was distributed under license by EUMETSAT. However, it is no longer supported by either EUMETSAT, Météo France or the NWP SAF. Prospective users are encouraged instead to use either one of the NWP SAF 1D-VAR packages or IAPP. The description of ICI (below) is retained for completeness.
The ICI inversion system was developed by Météo France/CMS. Its purpose is to reconstitute the vertical structure of the atmosphere in terms of temperature and moisture by inverting the radiative transfer equation. This is done by processing observations of sounder radiometers collected by an HRPT local station for the NOAA orbiting satellites.
The ICI system reads AAPP level1d TOVS/ATOVS incoming data that are navigated, temperature calibrated, mapped on the HIRS grid and documented after AAPP pre-processing. The maps that are presently being developed are the MSU on the HIRS grid for TOVS and the AMSU-A and AMSU-B on the HIRS grid for ATOVS. The main information associated with each HIRS fov are on the one hand the surface type (land/sea/mixed) and the altitude originating from topographic files and on the other hand the cloud cover and the skin surface temperature originating from the AVHRR cloud mask, and specifically for ATOVS, rainfall surface type flags originating from the AMSU preprocessing.
The inversion system is an operational system based on 5 main functional modules, which can be run at different moments of the day. They are :
- ICI: this is the software core. It is activated in 'real time' just after preprocessing a new acquisition. It reads the observations file in the level1d format as output of the AAPP preprocesses. It also reads some surface parameters predicted by a numerical weather prediction model in ASCII or GRIB format depending on parametrization, computes some cleared radiances when it is necessary, initializes the inversion by means of a likely atmospheric profile using ancillary analysis profiles or a climatology (guess), performs a 1D-Var inversion and writes the inverted profile into the output file. The software uses the RTTOV6 fast forward model inside the 1D-Var inversion.
- BASE METEO: the software supplies a local meteorological library comprising radiosoundings, analyses and temperature/moisture forecasts in altitude and on the surface. The purpose of BASE_METEO is to provide the ICI core module with forecasts, the BASE_PROFIL with analyses and the MONITORING with radiosoundings and analyses.
- BASE_PROFIL: this module creates a library of temperature and moisture atmospheric profiles. Profiles are used for initializing the inversion using a vertical profile which is very close to the restituted profile; they should therefore represent the meteorological situation encountered. The module finds information in the BASE_METEO when the latter is supplied on a regular basis or uses a climatological library (2 climatological libraries are available with ICI). Up and down radiances as well as total satellite-surface transmittances associated with each profile are computed with the RTTOV6 fast forward model.
- MONITORING: the purpose is first to adjust the inversion model so as to guarantee quality and stability for restituted profiles on a long-term basis by periodically re-adjusting the internal statistic coefficients of the ICI software (tuning) and second to perform a regular follow-up of quality (validation). Both actions are performed by using colocated data files (colocation) containing the satellite data, the inverted profile, the radiosounding and/or the nearest analysis in time and space.
- GRAPHIC DISPLAY: a set of graphic commands (using the freeware GMT library) and fortran codes have been added to the software for the visualization of the retrieved passes and their departure to NWP fields, and for the time display of the error statistics of key parameters (ex: forward RTTOV biases, RMSE of ICI temperature). An http page for putting all together these figures in gif format: it is an easy way for having a general view of the evolution of the software.
The ICI application is very modular through the use of two input permanent files. Their contents can be adjusted so as to meet specific users requirements. They are :
- PARAMETRES: this file contains all the parameters used for launching the ICI application. For example, it contains the sampling in pixel/line of the inversion, the format of the input/output data, the guess library definition. It can also cancel the update of internal coefficients (reinitialization of the tuning).
- ICIDIRS: this file contains the parametrized names of all the directories used in the scheme.
ICI inversion output files are sequential access binary files with one record per situation containing the level1d incoming data, environment data, surface weather forecasts, the atmospheric profile used for initializing the inversion as well as the restituted profile. Five coding routines can be activated by the parametrization so as to create the following files according to the user's requirements: ASCII files, mainly useful for coding colocated files, AAPP level2 standard files, SATEM, BUFR format files or finally GRIB meteorological standard files.