Trend Monitoring and in-flight Calibration Facility (TMCF) general description

The Trend Monitoring and in-flight Calibration Facility (TMCF) at the Royal Netherlands Meteorological Institute (KNMI) is a facility to monitor and maintain the calibration of the OMI instrument in flight.
The Ground Data Processing Software (GDPS) is the level 0-1b data processing software that processes raw instrument measurement data into geophysically calibrated quantities (Earth radiance and sun irradiance). The GDPS runs on the NASA OSIPS facility on Goddard Space Flight Center (GSFC) in Greenbelt (MD) in the United States. The GDPS has three types of output data products:

  • Earth radiance
  • Sun irradiance
  • Calibration data product

The GDPS uses a so-called Operational Parameters File (OPF), that contains all required OMI instrument calibration and characterisation data to process raw level-0 instrument data into calibrated level-1b data. The OPF contains both on-ground and in-flight calibration and characterisation data, for example:

  • Radiometric calibration for radiance and irradiance measurements.
  • Spectral calibration.
  • Geolocation calibration.
  • Stray light calibration.
  • Detector calibration: e.g. dark current maps for all measurement types, pixel-to-pixel gain map.
  • Electronics calibration: e.g. non-linearity functions, gain ratios, electronic offsets.
  • Thresholds for flagging limits: e.g. detector saturation, detector non-linearity, stray light.
A detailed description of the OPF can be found here.

One of the goals of the in-flight calibration is to monitor and maintain the accuracy of the OPF using in-flight measurement data. This is one of the major objectives of the TMCF. The TMCF hardware and software systems have been designed to:

  • Maintain the Level 0 to Level 1b (0-1b) calibration of the OMI in flight.
  • Deliver new OPFs that represent the status of the OMI performance and calibration for use in the GDPS.
  • Maintain an in-flight calibration database, partly automatically, partly semi-automatically (after user request).
  • Allow an operator to investigate the OMI in-flight instrument performance and calibration by accessing the in-flight calibration database and produce the required output, visual or otherwise.
  • Generate new OPF-entries based on information from the in-flight calibration database.
  • Automatically generate the required outputs (files, plots, prints, reports, etc.) to assess the status of the OMI in flight in terms of calibration and performance.
  • Automatically reduce the incoming Level 1b irradiance and calibration data products by appropriate averaging, and store the reduced data.
  • Perform limited quality assurance tasks on the incoming Level 1b irradiance and calibration data products.
  • Provide facilities for investigating Level 0 and Level 1b radiance, irradiance and calibration data products.
  • Support reprocessing of older data by providing the required OPFs.

In order to do this the radiance, irradiance and calibration level-1b files are sent to the TMCF system at KNMI. There they are split according to measurement configuration and version and subsequently averaged if required. This creates a number of new basic data products that exist only within the TMCF. These data products are used to perform the TMCF tasks as described above. In addition, the TMCF can run dedicated pieces of software (called Product Generation Executives or PGE's) that use as input some of the TMCF basic data products or one of the GDPS level-1b data products to produce derived output TMCF products that can be used for further investigations or assessments of the in-flight calibration. All TMCF data products are stored in the TMCF MySQL database, from which they can be retrieved with search queries. The ultimate goal is to use the available TMCF data products from the database to update and maintain the OPF so that it represents the most accurate and up-to-date status of the in-flight calibration and characterisation. This in turn ensures the most accurate level-0 to 1b data processing with the GDPS in the forward processing. Furthermore, new and more accurate OPF's can be prepared using the TMCF database data products for reprocessing of all available mission data since launch.

More details about the GDPS and the TMCF can be found in this document:

Data processing and in-flight calibration systems for OMI-EOS-Aura
Oord, G.H.J. van den, M. Dobber, J. van de Vegte, I. van der Neut, W. Som de Cerff, N.C. Rozemeijer, V. Schenkelaars, M. ter Linden,
Proceedings SPIE's Annual Meeting, San Diego (U.S.A.), 13 - 17 August 2006, Optics and Photonics 2006 (vol. 6296).    Full paper (PDF - 0.8 Mb).