TRMM/PR L1 Reflectiveities is obtained from the PR sensor onboard TRMM and produced by the Japan Aerospace Exploration Agency (JAXA). The Precipitation Radar (PR) is the primary instrument onboard TRMM. The most innovative of the five TRMM instruments, the PR is the first quantitative rain radar instrument to be flown in space. The major objectives of the PR instrument are as follows:a. Provides a 3-dimensional rainfall structureb. Achieves quantitative measurements of the rain rates over both land and ocean When properly combined with TMI measurements, the Precipitation Radar (PR) data is instrumental in obtaining the height profile of the precipitation content, from which the profile of latent heat release from the Earth can be estimated. The rain rate is estimated from the radar reflectivity factor when the rain rate is small by applying conventional algorithms used for ground-based radar. For large rain rates, a rain attenuation correction is made using the total-path attenuation of land or sea surface echoes.In PR Level 1 processing, Level 0 transmitted from NASA data is checked whether it is in an observation mode, and then three types of products are processed which are 1A21, 1B21, and 1C21. Moreover received power, noise level, Z factor including rain attenuation is calculated. However, 1A21 is actually processed within a same routine as 1B21, so 1A21 itself is not singly output. In 1C21 processing, the dummy radar reflectivity factor (Z factor: Zm) including rain attenuation during a rainfall is calculated using the radar equation, from the already calibrated received power value and noise level value calculated in the 1B21 processing.The provided format is HDF4. The Sampling resolution are 5km (horizontal) and 250m (range). The current version of the product is Version 7. The generation unit is orbit.