The International ATOVS Processing Package (IAPP)

The International ATOVS Processing Package (IAPP), and its predecessor the International TOVS Processing Package (ITPP), have been developed to retrieve atmospheric temperature and moisture profiles, total ozone and other parameters in both clear and cloudy atmospheres from ATOVS/TOVS radiance measurements.

The IAPP is designed to work with the AAPP (AVHRR and ATOVS Preprocessing Package) HIRS-3 level 1-D output file. The AAPP must be acquired independently from the NWP SAF.

The IAPP currently uses radiances from HIRS-3, AMSU-A, and AMSU-B on NOAA-15, -16, and -17 (and HIRS-4, AMSU-A and MHS on NOAA-18 and MetOp-A), preprocessed into the AAPP 1-D format, for retrieval. Ancillary data inputs for retrieval are high resolution topography (supplied), surface observations and numerical model data.
The IAPP algorithm retrieves the parameters in 4 steps: 1) cloud detection and removal; 2) bias adjustment; 3) regression retrieval; and 4) nonlinear iterative physical retrieval.
It performs temperature and moisture retrieval calculation on a 3x3 HIRS field of view (fov) matrix, or field-of-regard (FOR). HIRS and AMSU-A radiances are used for clear/cloudy fov determination. Depending on clouds, a HIRS + AMSU-A + AMSU-B retrieval, an AMSU-A + AMSU-B (i.e., no-HIRS) retrieval, or no retrieval is made for each FOR.

Surface data in the WMO Metar format is used, if available, to improve surface condition definition. If surface observations are not available, numerical model data is used (see next item) to define surface conditions, or, with neither available, window channel radiances are used to best approximate surface conditions. We strongly recommend using Metar surface information and/or NWP output to better describe surface conditions in retrieval processing.

Numerical model output can be used as a first guess field for the atmosphere and surface. Any model can readily be adapted to fit into the IAPP retrieval scheme. Clearly written documentation makes this task relatively straightforward. Alternatively, a regression scheme, based on synthetic radiance calculations, can be used to provide a first guess.

The output file is in NetCDF format.
Detailed information on the different steps is provided in the documentation.

A publication by Li, Wolf, Menzel, Zhang, Huang and Achtor, Journal of Applied Meteorology (August 2000) provides details on the algorithm.

For further details on IAPP, including how to obtain the package, please see the IAPP web page.