The Tropical Rainfall Measuring Mission (TRMM) is a joint U.S.-Japan  
                                    satellite mission to monitor tropical and subtropical precipitation   and to
                                    estimate its associated latent heating.
                                    
                                    The TRMM Precipitation Radar (PR), the first of its kind in space, is
                                    an electronically scanning radar, operating at 13.8 GHz that measures
                                    the 3-D rainfall distribution over both land and ocean, and defines
                                    the layer depth of the precipitation.
                                    
                                    The 1C21 calculates the effective radar reflectivity factor at 13.8
                                    GHz without any propagation loss (due to rain or any other atmospheric
                                    gas) correction (Zm). Therefore, the Zm value can be calculated just
                                    by applying a radar equation for volume scatter with PR system
                                    parameters. The noise-equivalent Zm is about 21 dBZ. Through the
                                    subtraction of the system noise, the Zm value as small as 16 or 18 dBZ
                                    are still usable although the data quality is marginal.  In 1C21, all
                                    echoes stored in 1B21 are converted to &quot;dBZ&quot; unit. This is not
                                    relevant for &quot;non-rain&quot; echo; however, this policy is adopted so that
                                    the 1B21 and 1C21 product format should be as close as possible except
                                    for the following points:
                                    
                                    - Radar quantity is Zm in dBZ unit instead of received power (dBm).
                                    - Data at echo-free range bins judged in 1B21 are replaced with a dummy
                                      value.
                                    
                                    The data are stored in the Hierarchical Data Format (HDF), which
                                    includes both core and product specific metadata applicable to the PR
                                    measurements.  A file contains a single orbit of data with a file size
                                    of about 139 MB (uncompressed). The HDF-EOS &quot;swath&quot; structure is used
                                    to accommodate the actual geophysical data arrays. There are 16 files
                                    each of PR 1B21 and 1C21 data produced per day.
                                    
                                    Spatial coverage is between 38 degrees North and 38 degrees South,
                                    owing to the 35 degree inclination of the TRMM satellite. This orbit
                                    provides extensive coverage in the tropics and allows each location to
                                    be covered at a different local time each day, enabling the analysis
                                    of the diurnal cycle of precipitation. There are, in general, 9150
                                    scans along the orbit, with each scan consisting of 49 rays.  The scan
                                    width is about 220 km.