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Description
These data originate from NOAA/NCEP.
The NOAA Climate Prediction Center/NCEP/NWS is making the data available originally in binary format, in a weekly rotating archive. The NASA GES DISC is acquiring the binary files as they become available, converts them into CF (Climate and Forecast) -convention compliant netCDF-4 format, and stores the product in a permanent archive. The original record started from February, 2000, but in June, 2025 it was extended back to January, 1998.
The leading edge of data availability is delayed by about 24 hours from real-time to abide by international data exchange agreements between NOAA and EUMETSAT (the METEOSAT data providers).
The data contain globally-merged (60°S-60°N) 4-km pixel-resolution IR brightness temperature data (equivalent blackbody temps), merged from the European, Japanese, and U.S. geostationary satellites over the period of record (GOES-8/9/10/11/12/13/14/15/16/17/18/19, METEOSAT-5/7/8/9/10/11, and GMS-5/MTSat-1R/2/Himawari-8/9).
The global geo-IR are dynamically calibrated to GOES East, using a 35 day trailing inter-calibration using time/space-matched IR Tb’s at the mid-point between sub-satellite positions. In the event of duplicate data in a grid box, the value with the smaller zenith angle is taken. The data have been corrected for "zenith angle dependence", in which IR temperatures for locations far from satellite nadir are erroneously cold due to a combination of geometric effects and radiometric path extinction effects (Joyce et al. 2001). Finally, the data are re-navigated for parallax, which shifts the geo-location of the GEO-IR footprints to approximately account for the cloud tops that the IR “sees” being displaced away from their actual geographic location when viewed along a slanted path. These corrections allow for the merging of the IR data from the various GEO-satellites with greatly reduced discontinuities at GEO-satellite data boundaries. In the event of duplicate data in a grid box, the value with the smaller zenith angle is taken.
The NASA GES DISC is curating these data in a self-documenting, CF-compliant, netCDF-4 format, which allows a broad range of applications to access the data directly, without the need to cope with the original binary data format. In addition to the direct download of netCDF-4 data, the GES DISC provides data download in binary, ASCII, and netCDF-3 formats using the OPeNDAP interface which also provides remote data access.
Similarities with the original
As in the original binaries, every netCDF-4 file covers one hour, and contains two half-hourly grids, at 4-km grid cell resolution.
Differences from the original
The data in the netCDF-4 files are already converted to physical values of Brightness Temperatures in Kelvin. Because the original data values are round with no decimal precision, the data type in the netCDF-4 files has been changed to 2-byte signed integer, a transition that took place in mid-August, 2025. This reduces the file size and speeds up data download and remote access. There is no need to further scale these data. The netCDF-4 format is machine-independent and users need not worry about the endian-ness of their machines.
To meet the requirements of collection spatial metadata, the grid is re-ordered from the original and now goes from -180 (West) to 180 (East). It is also starting from -60 (South).
The data and time units are reflected in the corresponding "units" attributes, and grid dimensions are described by longitude ("lon"), latitude ("lat") and "time" vectors. Thus, any CF-compliant tool should automatically understand the setup in the data files and the starting time for each half-hourly grid. Even without such tools, simple "ncdump" or "h5dump" command line tools will easily disclose the netCDF-4 files configuration.
Acknowledgements
The creation of the original data at NOAA/NCEP is supported by funding from the NOAA Office of Global Programs for the Global Precipitation Climatology Project (GPCP) and by NASA via the Tropical Rainfall Measuring Mission (TRMM).
The permanent archive at GES DISC is supported by NASA's HQ Earth Science Data Systems (ESDS) Program.
Product Summary
Platforms
IMERG
Instruments
NOT APPLICABLE
Spatial Extent
N: 60S: -60E: 180W: -180
Location
EQUATORIAL
,
MID-LATITUDE
Coordinate System
CARTESIAN
Granule Spatial Representation
CARTESIAN
Temporal Extent
1998-01-01 to Present
Data Partner
Goddard Earth Sciences Data and Information Services Center (formerly Goddard DAAC), Terrestrial Information Systems Laboratory, Earth Sciences Division, Science and Exploration Directorate, Goddard Space Flight Center, NASA (NASA/GSFC/SED/ESD/TISL/GESDI
Citation is critically important for dataset documentation and discovery. This dataset is openly shared, without restriction, in accordance with the EOSDIS Data Use and Citation Guidance.
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Citation Copied
Janowiak, J., Joyce, B., & Xie, P. (2017). NCEP/CPC L3 Half Hourly 4km Global (60S - 60N) Merged IR V1 [Data set]. NASA Goddard Earth Sciences Data and Information Services Center. https://doi.org/10.5067/P4HZB9N27EKU Date Accessed: 2026-05-23
Janowiak, John, Bob Joyce, and Pingping Xie. “NCEP/CPC L3 Half Hourly 4km Global (60S - 60N) Merged IR V1.” NASA Goddard Earth Sciences Data and Information Services Center, 2017. doi:10.5067/P4HZB9N27EKU. Date Accessed: 2026-05-23
Janowiak, John, et al. NCEP/CPC L3 Half Hourly 4km Global (60S - 60N) Merged IR V1. NASA Goddard Earth Sciences Data and Information Services Center, 2017, doi:10.5067/P4HZB9N27EKU. Date Accessed: 2026-05-23
Feng, Zhe, Prein, Andreas F., Kukulies, Julia, Fiolleau, Thomas, Jones, William K., Maybee, Ben, Moon, Zachary L., Nunez Ocasio, Kelly M., Dong, Wenhao, Molina, Maria J., Albright, Mary Grace, Rajagopal, Manikandan, Robledo, Vanessa, Song, Jinyan, Song, Fengfei, Leung, L. Ruby, Varble, Adam C., Klein, Cornelia, Roca, Remy, Feng, Ran, Mejia, John F.
The table below lists the variables contained within a single granule for this
dataset. Variables often contain observed or derived geophysical measurements
collected from a variety of sources, including remote sensing instruments on
satellite and airborne platforms, field campaigns, in situ measurements, and
model outputs. The terms variable, parameter, scientific data set, layer, and band
have been used across NASA’s Earth science disciplines; however, variable is the
designated nomenclature in NASA’s Common Metadata Repository (CMR).
Variable metadata attributes such as Name, Description, Units, Data Type, Fill
Value, Valid Range, and Scale Factor allow users to efficiently process and analyze
the data. The full range of attributes may not be applicable to all variables.
Additional information on variable attributes is typically available in the data,
user guide, and/or other product documentation.
For questions on a specific variable, please use the Earthdata Forum.