The construction of continuing, stable, and accurate global precipitation analyses from observations from a continually changing international constellation of research and operational satellites is a fundamental but daunting challenge for the development of satellite-based global climate data records.¹⁵ Fulfillment of this task depends on a number of factors, of which the following two are central:

1. Climate data records depend on the maintenance of an international constellation of satellites that provide the routine time-space sampling needed for high-quality global precipitation analyses. For example, the design sampling interval of the GPM constellation of passive microwave sensors is 3 hours. International coordination to improve the phasing of polar-orbiting satellites could be a factor for improving sampling.

2. Climate data records depend on an ongoing and extensive international program for intercalibration of satellite radiances. Without intercalibration to remove biases, and an understanding and quantification of the error characteristics of the observations, the measurements are of marginal value for climate applications, since drifts in satellite sensors can produce spurious trends in the time series, and jumps can occur in a time series due to systematic biases from different sensor observations.

The planned observational and calibration-validation programs of the GPM mission will address many of the current deficiencies that limit the development of satellite-based global precipitation climate data records.

The best operational uses of GPM data at NOAA will be weather forecasting, hydrologic applications, climate applications, and global precipitation climate data records. Prior to the launch of the GPM core satellite, NOAA can initiate improvements in current sources of precipitation data and improvements in data products to enhance the operational benefits of the GPM mission. Chapter 4 outlines additional preparation activities at NOAA for optimal use of GPM data by the launch of the GPM core satellite.