Precipitation Data Directory

This algorithm is intended to intercalibrate, merge, and interpolate “all” satellite microwave precipitation estimates, together with microwave-calibrated infrared (IR) satellite estimates, precipitation gauge analyses, and potentially other precipitation estimators at fine time and space scales for the TRMM and GPM eras over the entire globe. The system is run several times for each observation time, first giving a quick estimate (IMERG Early Run) and successively providing better estimates as more data arrive (IMERG Late Run). The final step uses monthly gauge data to create research-level products (IMERG Final Run).

The main difference between the IMERG Early and Late Run is that Early only has forward propagation (which basically amounts to extrapolation) due to the short latency, while the Late has both forward and backward propagation (allowing interpolation).

Notes:

• The PPS has completed reprocessing GPM IMERG data for IMERG V07B. The IMERG dataset now includes TRMM-era data going back to January 1998.
• As of IMERG V7B, full coverage is provided at all latitudes, except for a few boxes very near the poles,

This algorithm is intended to intercalibrate, merge, and interpolate “all” satellite microwave precipitation estimates, together with microwave-calibrated infrared (IR) satellite estimates, precipitation gauge analyses, and potentially other precipitation estimators at fine time and space scales for the TRMM and GPM eras over the entire globe. The system is run several times for each observation time, first giving a quick estimate (IMERG Early Run) and successively providing better estimates as more data arrive (IMERG Late Run). The final step uses monthly gauge data to create research-level products (IMERG Final Run). 

The main difference between the IMERG Early and Late Run is that Early only has forward propagation (which basically amounts to extrapolation), while the Late has both forward and backward propagation (allowing interpolation). The additional 10 hours of latency allows lagging data transmissions to make it into the Late run, even if they were not available for the Early. 

Notes:

• The PPS has completed reprocessing GPM IMERG data for IMERG V07B. The IMERG dataset now includes TRMM-era data going back to January 1998.
• As of IMERG V7B, full coverage is provided at all latitudes, except for a few boxes very near the poles,

This algorithm is intended to intercalibrate, merge, and interpolate “all” satellite microwave precipitation estimates, together with microwave-calibrated infrared (IR) satellite estimates, precipitation gauge analyses, and potentially other precipitation estimators at fine time and space scales for the TRMM and GPM eras over the entire globe. The system is run several times for each observation time, first giving a quick estimate (IMERG Early Run) and successively providing better estimates as more data arrive (IMERG Late Run). The final step uses monthly gauge data to create research-level products (IMERG Final Run).

The main differences between the IMERG Early and Late Run are:

• The half-hourly Final Run product uses a month-to-month adjustment to the monthly Final Run product, which combines the multi-satellite data for the month with GPCC gauge analysis. The adjustment within the month in each half hour is a ratio multiplier that's fixed for the month, but spatially varying.
• The Late Run is computed about 14 hours after observation time, so sometimes a microwave overpass is not delivered in time for the Late Run, but subsequently comes in and can be used in the Final.  This would affect both the half hour in which the overpass occurs, and (potentially) morphed values in nearby half hours.

We always advise people to use the Final Run for research unless their application will require the use of Early or Late data due to latency. In such a case, the application should be developed using the long-record of the Early or Late, as appropriate. The vast majority of grid boxes have fairly similar Late and Final values over ocean, and to a lesser extent over land. Extreme value statistics are more sensitive to these details; medians, means, and root-mean square difference are less sensitive. 

Notes:

• The PPS has completed reprocessing GPM IMERG data for IMERG V07B. The IMERG dataset now includes TRMM-era data going back to January 1998.
• As of IMERG V7B, full coverage is provided at all latitudes, except for a few boxes very near the poles,

The GPM Combined Radar-Radiometer Algorithm performs two basic functions: first, it provides, in principle, the most accurate, high resolution estimates of surface rainfall rate and precipitation vertical distributions that can be achieved from a spaceborne platform, and it is therefore valuable for applications where information regarding instantaneous storm structure are vital. Second, a global, representative collection of combined algorithm estimates will yield a single common reference dataset that can be used to “cross-calibrate” rain rate estimates from all of the passive microwave radiometers in the GPM constellation. The cross-calibration of radiometer estimates is crucial for developing a consistent, high time-resolution precipitation record for climate science and prediction model validation applications.

The Level 3 DPR product provides space-time statistics of the level 2 DPR results. High and low spatial resolution grids are defined such that the high-resolution grid is 0.250 × 0.250 (lat×lon) while the low resolution grid is 50 × 50. For the variables defined on the low-resolution grid, the statistics include mean, standard deviation, counts and histogram. For variables defined on the high-resolution grid, the same statistics are computed with the exception of a histogram, which is omitted.

3GPROF, 'GPROF Profiling', produces global 0.25 degree x 0.25 degree gridded means using Level 2 Gprof data. Vertical hydrometeor profiles and surface rainfall means are computed. Various pixel counts are also reported. The PI is Joyce Chou. The product can be monthly or daily.