Merged-data products critically depend on the input sensors and the retrieval algorithms providing accurate, reliable estimates, but it is also important to provide ancillary information that helps users determine suitability for their application. We typically provide fields of estimated random error, and recently reintroduced the quality index concept at user request. Also at user request we have added a (diagnostic) field of estimated precipitation phase. Over time, increasingly more ancillary fields have been introduced for intermediate products that give expert users insight into the detailed performance of the combination algorithm, such as individual merged microwave and microwave-calibrated infrared estimates, the contributing microwave sensor types, and the relative influence of the infrared estimate.
One growing trend is the means of disseminating the precipitation data sets. Originally, locally designed binary formats emphasized compactness and simplicity, but standard formats (HDF5, NetCDF) have become the norm for the native data sets, and these are distributed in a variety of user-requested formats and web services, often with on-the-fly compression and subsetting by location and parameter. Another trend in data dissemination has been the shift from creating a single time series of “research” products to creating multiple products with different latencies that (in GPM) support rapid-turnaround, next-day, and archive-quality uses (latencies of ~4 hr, ~14 hr, and ~3 months, respectively). Based on strong feedback, users require that all three products must be uniformly retrospectively processed when a new version of the algorithm is introduced. This ensures that all products provide a long, homogeneously processed record that can support various user-implemented calibration schemes.
User support has similarly evolved, moving from the original expert-oriented README files to the current more-comprehensive https://pmm.nasa.gov web site, which provides pages for a range of documentation, Frequently Asked Questions, Ask-A-Question, example visualizations, and data access. The data access pages are a one-stop shop for all the schemes that give access to TMPA, IMERG, the other TRMM and GPM products, and value-added products in the Goddard environment. This includes the innovative, user-friendly https://giovanni.gsfc.nasa.gov/giovanni/ site, hosted by the Goddard Earth Sciences Data and Information Services Center (GES DISC) that provides basic on-line display and analysis without requiring the user to download any data or confront understanding the various data formats. NASA has funded the reformatting required to add GPCP and TMPA (shifting to IMERG next year) to the Obs4MIPS archive that is compatible with CMIP standards, as well as funding custom product releases to NOAA through the Short-term Prediction Research and Transition (SPoRT) Center. Note that there are additional secondary archives of the GPCP, TRMM, and GPM products, some with additional value-added offerings. This can make user support challenging since the algorithm development teams are not privy to the details of these archives, nor can they verify the secondary archives’ correctness and timeliness. Another enhancement in user support is NASA-funded training activities, for example through the Applied Remote Sensing Training (ARSET) activity and through GPM training webinars. As well, NASA Applied Sciences and GPM have jointly sponsored user workshops.
Finally, the tremendous progress in merged-data precipitation products has benefitted from the increased number of satellite passive microwave sensors over the last 15 years. We are now facing the potential for this constellation of opportunity to decline over the next decade and need to explore creative ways to maintain the constellation and continue providing the high-quality precipitation products that users have come to expect.
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