GPM/DPR Level-3 Algorithm Theoretical Basis Document (ATBD)
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 lowresolution 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.
The level 3 code is written so that the 15 or 16 orbits of level 2 DPR data produced daily can optionally be processed in two runs, where one output file contains statistics from the ascending orbital passes while the other file contains statistics from the descending passes. Since all orbits for the day are processed in each run, there is no need for intermediate files. What is produced are two daily level 3 HDF files. Nominally, the standard level 3 product will be obtained by processing the twice-daily HDF files over a calendar month; however, this is not required. In particular, output products can be generated from any set of daily HDF files. It should be noted that the daily files will contain a mean square statistic rather than the standard deviation. For the monthly (or multi-day) file, however, the mean square statistic will be replaced with the standard deviation.