Current version: v8.8, August 2021

The ATOVS and AVHRR Pre-processing Package (AAPP) is supplied and maintained by the NWP SAF. This package processes data from instruments on board the NOAA POES polar orbiting satellites – namely HIRS, AVHRR, AMSU and MHS – and from HIRS, AVHRR, AMSU, MHS and IASI on the European METOP satellites. For these satellites AAPP can ingest and process raw direct readout data. It also processes Sensor Data Record data from the new-generation Suomi NPP satellite, and from the sounders on the Chinese FY-3 satellites.

As its main output, AAPP produces files of quality-controlled brightness temperature or radiance data for each instrument – either separately or mapped to a common field of view. An AVHRR cloud mask can also be generated. If profiles of atmospheric variables are required, the AAPP can be used in conjunction with an inversion package. AAPP radiance data are also used directly as input to variational data assimilation systems at several leading centres for Numerical Weather Prediction.

AAPP development is closely linked to the activities and recommendations of the International TOVS Working Group (ITWG).

Questions for other users and developers can be posted on the AAPP Forum.

Supported Instruments

AAPP performs end-to-end processing of Sounding and Imager Data from the HRPT (High Resolution Picture Transmission) direct readout data stream of the TIROS-N/NOAA satellites and also their successors of the NOAA-KLM satellite series, from 1998 onwards. AAPP also processes data from the European METOP satellites.

TIROS/NOAA satellites

Data from the following instruments can be processed:




For NOAA satellites, AAPP performs the following tasks:

  • decommutation of the instrument data from the HRPT data frame
  • extraction of the calibration information
  • navigation of the data
  • calibration of the data
  • pre-processing of the data (cloud mask included)
  • mapping of the data of the sounder instruments on a common instrument grid (HIRS, AMSU, MHS or IASI)
  • deriving a set of statistical parameters from the AVHRR data in the HIRS FOVs

MetOp Satellites


For METOP, AAPP ingests “EPS Level 0” files (one file per instrument), then performs navigation, calibration and pre-processing as above.

In the case of IASI, level 1 processing is performed by the OPS-LRS (Operational Software – Local Reception Station), which is an optional extension to AAPP and is based on the OPS software provided to EUMETSAT by CNES.

Other Satellites



For NPP, the starting points for AAPP are Sensor Data Record files (SDR). For direct readout, you will need an external program, such as University of Wisconsin’s CSPP package, or NASA’s IPOPP package, to generate the SDR files. The same applies to FY-3, for which the China Meteorological Administration provide a processing package for direct readout use.

Supplementary Modules for AAPP

Supplementary Modules perform the processing of Orbital information and provide the following services:

  • decoding of TBUS/TLE/SPOT Messages
  • creation of a TBUS/TLE/SPOT data base
  • creation of a data base of on board clock errors
  • analysis of antenna reception conflicts
  • antenna tracking coordinates

In the course of the processing the following files are created for each instrument:

  • level 1a = instrument counts
  • level 1b = instrument counts, navigation and calibration information appended
  • level 1c = instrument reflectance factors or brightness temperatures, navigation and calibration information appended
  • level 1d = instrument reflectance factors or brightness temperatures, mapped on one common instrument grid, navigation, calibration and contamination information appended

From the Navigation step the resulting files are created:

  • TBUS/TLE/SPOT files
  • ephemeris files
  • clock error files
  • tracking files


AAPP-related Publications