The Global Precipitation Climatology Project (GPCP) daily precipitation is produced at the NASA Goddard Space Flight Center. The precipitation estimates are derived by different methods in the tropics and the extratropics, and the documentation available at the above WWW page provides a detailed discussion and reference.
The GPCP is managed by Robert Adler, and it is a component of the Global Energy and Water Cycle Experiment of the World Climate Research Program. GPCP is an ongoing project, and updates and new algorithms are always being developed, so users are advised to to check the NASA GSFC WWW page to see if there is a newer product that replaces this one. The updates of the data seem to lag reality by 2-3 months. I will not be updating the netCDF version of this data set until I have a need for updated data. Please send questions or comments about the product to George Huffman.
Bolvin, D. T., R. F. Adler, G. J. Huffman, E. J. Nelkin, J. P. Poutiainen, 2009: Comparison of GPCP monthly and daily precipitation estimates with high-latitude gauge observations. J. Appl. Meteor. Climatol., accepted.
Huffman, G. J.,R. F. Adler, M. M. Morrissey, S. Curtis, R. Joyce, B. McGavock, and J. Susskind, 2001: Global precipitation at one-degree daily resolution from multi-satellite observations. J. Hydrometeor., 2, 36-50.
Yin, X., A. Gruber, and P. Arkinc, 2004: Comparison of the GPCP and CMAP Merged Gauge-Satellite Monthly Precipitation Products for the Period 1979-2001. J. Hydromet., 5, 1207-1222.
Note: The GPCP algorithms are always being updated so you are advised to check the GPCP WWW page to make sure that you are getting the latest and greatest version of this data set.