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. TRMM was successfully
                        launched on November 27, at 4:27 PM (EST) from the Tanegashima Space
                        Center in Japan.
                        
                        The TRMM Microwave Imager (TMI) is a nine-channel passive microwave
                        radiometer, which builds on the heritage of the Special Sensor
                        Microwave/Imager (SSM/I) instrument flown aboard the Defense
                        Meteorological Satellite Program (DMSP) platforms. Microwave radiation
                        is emitted by the Earth&apos;s surface and by water droplets within
                        clouds. However, when layers of large ice particles are present in
                        upper cloud regions - a condition highly correlated with heavy
                        rainfall - microwave radiation tends to scatter at frequencies above
                        19 GHz. The TMI detects radiation at five frequencies chosen to
                        discriminate among these processes, thus revealing the likelihood of
                        rainfall. The key to accurate retrieval of rainfall rates by this
                        method is the deduction of cloud precipitation consistent with the
                        radiation measurement at each frequency. The TMI frequencies are
                        10.65, 19.35, 37 and 85.5 GHz (dual polarization), and 21 GHz
                        (vertical polarization only).
                        
                        The TMI Gridded Oceanic Rainfall Product, also known as TMI Emission,
                        consists of 5 degree by 5 degree monthly oceanic rainfall maps using
                        TMI Level 1 data as input. Statistics of the monthly rainfall,
                        including number of samples, standard deviation, goodness-of-fit (of
                        the brightness temperature histogram to the lognormal rainfall
                        distribution function) and rainfall probability are also included in
                        the output for each grid box. Spatial coverage is between 40 degrees
                        North and 40 degrees South owing to the 35 degree inclination of the
                        TRMM satellite.
                        
                        TMI brightness temperature histograms at 1 degree intervals are
                        generated based on the 19, 21 and 19-21 GHz combination channels
                        obtained from the Level 1B (calibrated brightness temperature) TMI
                        product. Monthly rainfall indices over the ocean are derived by
                        statistically matching monthly histograms of brightness temperatures
                        with model calculated rainfall Probability Distribution Functions
                        (PDF) using the 19-21 GHz combination data. Retrieved monthly rainfall
                        data must pass a quality test based on the quality of the PDF fit.
                        
                        The data are stored in the Hierarchical Data Format (HDF), which
                        includes both core and product specific metadata applicable to the TMI
                        measurements. A file contains 12 arrays of rainfall data and
                        supporting information each of dimension 72 x 16, with a file size of
                        about 40 KB (uncompressed). The HDF-EOS &quot;grid&quot; structure is used to
                        accommodate the actual geophysical data arrays. There is 1 file
                        of TMI 3A11 data produced per month.