IMERG Final Run
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.
- The PPS has completed reprocessing GPM IMERG data for IMERG V06B. The IMERG dataset now includes TRMM-era data going back to June 2000.
- As of IMERG V05B, full coverage is provided for the latitudes of 60°N-60°S, while the remaining upper and lower latitudes extending to 90° are considered "partial coverage".