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NWP SAF Aerosol and Cloud Detection Package for High Resolution Infrared Sounders

Version 1.3 released 1st December 2011

What's new in version 1.3: Capability to process data from the Cross-track Infrared Sounder is introduced. Implementation of the cross-band option is made more cautious than in earlier versions. Default cloud detection bands of AIRS are revised to improve performance of the scheme on short-wave channels. A bug found in one of the source files is corrected such that cloud-contaminated channels are more successfully identified in certain type of cases.

This cloud and aerosol detection software is based on a pattern recognition algorithm developed for the detection of clouds in AIRS spectra.

The cloud detection algorithm works by taking the first guess departures (i.e., the difference between the observed brightness temperatures and brightness temperatues calculated from a good estimate of the atmospheric state - typically a 6-hour forecast from an NWP model) and looking for the signature of opacity that is not included in the clear-sky calculation (i.e. cloud or aerosol). The aerosol code decides whether an observation, initially defined as being cloud affected, is in fact mainly affected by aerosol. Identification of aerosol contamination is based on first guess departures of window channels in the 8µm region.

The software package is NWP-dependent (i.e., requires an estimate of the atmospheric state vector), but is sufficiently modular to "plug-in" to most NWP systems.

Input data: For each channel selected in the FOV, the algorithm requires the background (model) brightness temperature, the observed brightness temperature and a height assignment for each channel in units defined by the user (e.g., NWP model level, pressure level).

Output data: Output file is produced containing flags indicating clear, cloud-contaminated and aerosol-contaminated channels in each input satellite sounding.

  • Further information
    • McNally, A.P. and P.D. Watts, 2003. A cloud detection algorithm for high-spectral-resolution infrared sounders, Q J Roy Meteorol Soc, 129, 3411-3423.
    • User Manual
  • Brief outline of plans
    • Continue improving the algorithm, releasing updates as appropriate.
    • Feasibility of making extended use of short-wave data in night-time conditions is under investigation.
    • A facility for discrimination of different types of aerosols will be added if testing proves successful.

The Aerosol and Cloud Detection package can be requested using this form.