Spatial Resolution: 0.07277 degrees lat/lon (8 km at the equator)
Temporal Resolution: 30 minutes
Domain: Global (60N - 60S)
Period of Record: Nov. 26, 2002 to present

This technique uses precipitation estimates that have been derived from low orbiter satellite microwave observations exclusively, and whose features are transported via spatial propagation information that is obtained entirely from geostationary satellite IR data. At present we incorporate precipitation estimates derived from the passive microwaves aboard the DMSP 13, 14 & 15 (SSM/I), the NOAA-15, 16 & 17 (AMSU-B) and the TRMM (TMI) spacecraft (see CPC Merged Microwave Product). We hope to include estimates soon from the AMSR and AMSR-E sensors aboard Aqua and ADEOS-II, respectively. Note that this technique is not a precipitation estimation algorithm but a means by which estimates from existing microwave rainfall algorithms can be combined. Therefore, this method is extremely flexible such that any precipitation estimates from any microwave satellite source can be incorporated.

In effect, IR data are used as a means to transport the microwave-derived precipitation features during periods when microwave data are not available at a location. Propagation vector matrices are produced by computing spatial lag correlations on successive images of geostationary satellite IR which are then used to propagate the microwave derived precipitation estimates. This process governs the movement of the precipitation features only. At a given location, the shape and intensity of the precipitation features in the intervening half hour periods between microwave scans are determined by performing a time-weighting interpolation between microwave-derived features that have been propagated forward in time from the previous microwave observation and those that have been propagated backward in time from the following microwave scan. We refer to this latter step as "morphing" of the features.

An hour-by-hour comparison of a squall line over the U.S. among purely passive microwave data (top), our propagated analyses (middle), and radar (bottom). The white areas in the plot indicate where no passive microwave data were available; gray background color means no precipitation. This squall line case illustrates the good agreement with radar in our propagated analyses. Note the good positioning of features in the 06Z analysis, a time for which no new microwave data had been available for 3 straight hours.

A paper that describes this method is being prepared. To learn more about it in the mean time, contact:

Bob Joyce (robert.joyce@noaa.gov)
John Janowiak (john.janowiak@noaa.gov)
Phil Arkin (parkin@essic.umd.edu)
Pingping Xie (pingping.xie@noaa.gov)