Detailed information on AAPP

AAPP is the response to the demand of a large User Community for a standardized software for the processing of direct readout HRPT data of TIROS-N/NOAA, NOAA-KLM and METOP series satellites. For a long time many different types of code have been available to perform the processing steps from the received raw data ('from the antenna') to the pre-processed, calibrated and navigated data ('to the product'). These processing steps can be standardized, so that the retrieval step(s), in which the essential different scientific approaches are embedded, can be based on the same input data and thus a manifold of Users can apply satellite data in an efficient way.

Another advantage of AAPP is that it will be maintained centrally (by the NWP SAF), e.g. in case of necessary updates for new space craft instruments the calibration coefficients will be made available through updated versions of AAPP.

The AAPP web pages provide a forum to exchange experiences in the use of AAPP, to make bugs known, and to get the information dispatched to specialists in the respective fields.

Navigation

AAPP uses a processed TBUS message for the processing of orbital information. With the aid of the BROLYD (Brower/Lyddane) algorithm orbital parameters are predicted for the over pass in question, and with the instrument information available, the correct position of an instrument scan pixel on the Earth's surface, together with the correct time annotation, can be estimated.
TBUS messages can be received from e.g. following sites:
i)    The most recent TBUS message via the internet from NOAASIS.
ii)   TBUS messages for the past year, plus access to historical tbus messages, from NOAASIS.
iii)   Historical TBUS messages via ftp from the University of Tokyo (ftp://ftp.tkl.iis.u-tokyo.ac.jp/pub/TBUS).

AAPP version 5 onwards can accept Two-line element(TLE) data as an alternative to TBUS. TLE bulletins are available from www.space-track.org, and AAPP includes a script to retrieve and process the latest bulletin.

For METOP, TLEs are available either via the METOP Multi-Mission Administrative Message (MMAM) or from the EUMETSAT web site. AAPP was designed to process the SPOT bulletins that were available in the Metop-A Admin message prior to 2013, but these have now been retired.

Decommutation

 

The decommutation step for NOAA satellites separates the instrument data contained in an HRPT frame. The AAPP standard distribution uses the data exactly in the format described in the NESS/NOAA TM 107 - Rev. 1 (Planet, W. G. (Editor), 1988) and also in the NOAA-KLM User's Guide, but expects the original downlinked 10 bit words unpacked by being stored right justified in 16 bit words. An unpacking tool is available if your data are in packed format, but you may need to modify the tool to suit your data. The data of the TIROS Information Processor (TIP) and the AMSU Information Processor (AIP) as well as the multiplexed AVHRR data from five channels will be decommutated and stored in the respective instrument specific HRPT level 1a files.

 

For METOP the input to AAPP is the EPS Level 0 format defined by EUMETSAT. The instruments are supplied in separate files and therefore there is no decommutation step. If your reception system does not deliver EPS Level 0 format, you may wish to make use of the METOPIzer tool supplied by EUMETSAT.

 

Calibration

 

Calibration means the extraction of the onboard calibration parameters (e.g. Black Body Counts, Space counts etc.) from the data stream, the transformation of these counts into calibration coefficients, and finally the application of these calibration coefficients to the Earth Observation data, to transform them from binary units (counts) into physical parameters (Brightness Temperatures or Reflectance Factors).

 

Pre-Processing

 

Pre-Processing means the detection and flagging of all information in the data which are deemed non suitable for use in the subsequent retrieval step. These contamination effects include effects by large rain drops, ice particles in clouds, surface effects etc. The current baseline does not include correction of these effects. Furthermore a cloud clearing step is performed and corresponding information is passed on. A second task of the pre-processor is the mapping of all sounder instrument data to a common grid to be used in the retrieval step. This may be the HIRS, AMSU-A, AMSU-B or IASI grid.

 

Mapping

 

As stated above mapping means the transfer of the information from the FOV-grid of one given instrument to the FOV-grid of another. For ATOVS, the AMSU-B/MHS data are mapped first to AMSU-A FOV and these data and the AMSU-A data are mapped then to the HIRS FOV. Optionally AMSU-A may also be mapped to the AMSU-B (or MHS) grid. For TOVS, the MSU data are mapped to the HIRS FOV. AVHRR data are mapped to the HIRS FOV in form of statistical parameters. For METOP, AMSU-A and MHS may in addition be mapped to the IASI grid.

 

Tracking

 

Tracking means the creation of information concerning the visibility of overpasses for a given reception station. The station coordinates and a recent set of orbital information must be known.

 

NOAA Level 1B File Formats

 

The AAPP internal level 1b file format is similar to the level 1b file format for the NOAA-KLM satellites defined by NOAA/NESDIS (NESDIS NOAA-KLM Level 1b data specification). This applies to the AAPP processing of ATOVS data as well as TOVS data. Nevertheless, there are slight differences in the AVHRR and HIRS l1b file formats between AAPP and NOAA/NESDIS. AAPP has been prepared to cope with the differences. Therefore, unpacked NOAA/NESDIS level 1b data from NOAA-KLM satellites can be ingested into AAPP. From AAPP v7.6, conversion tools are provided at allow AAPP to accept level 1b data from TIROS-N series satellites, and to convert NOAA GAC/LAC/HRPT l1b files from NOAA's CLASS archive to standard AAPP l1b format.

 

IASI level 1 processing

 

Processing of IASI data from level 0 to level 1c is performed by the IASI OPS-LRS, available as an optional component of AAPP. Note that this software uses multithreaded techniques and is more difficult to run than the ATOVS processing modules. Furthermore not all platforms are supported (e.g. HPUX and IRIX are not). For more details on OPS-LRS, please consult the OPS-LRS User Manual.

 

BUFR encoding and decoding

 

AAPP version 6 onwards has tools to encode and decode BUFR level 1c data. This format is widely used for international data exchange. The AAPP tools make use of the ECMWF BUFR library, which must be downloaded from ECMWF if the tools are required.

 

HDF5 capability

 

AAPP version 7 has tools to ingest and pre-process hdf5 files from the Suomi-NPP and FY-3 satellites. For details on installing hdf5 libraries, please see the AAPP Installation Guide.

 

AAPP is designed for UNIX or Linux systems. The software has been tested on a range of systems, including Linux PC, HPUX, Sun Solaris, IBM AIX and SGI IRIX systems. It may also be run on Windows PC using a Unix emulator.

The following components are needed:

• UNIX or Linux operating system
• FORTRAN 77 or Fortran 90 compiler
• make utilities
• tar, gzip and gunzip
• perl
• about 400 MB of free disk space
• KORN shell (adaptations required to BASH and C-shell)
• potentially X-Window.

Basically nothing on ATOVS except the HRPT format your reception station delivers out of the frame synchronizer (in the case of NOAA satellites). This determines the amount of changes you have to implement in the routine decommutation.F. Note that AAPP expects the HRPT data unpacked right justified in 16 bit words; if this is not the case you may be able to use the tool unpack_noaa_hrpt.

You will also have to arrange for the appropriate input files to be presented to AAPP - especially in the case of METOP where there is a separate Level 0 file for each instrument.