TRMM/PR L1 Received Power 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 1B21 processing, the radar video signal digital count value is converted into a received power value as well as a noise level value in accordance with the algorithm (calibration of received power based on temperature calibration as well as transfer function) created based on the radiometric model of the precipitation radar. Longitude and latitude information of ground surface is added to convert this value into radar reflectivity factor (Z factor) including rain attenuation. Also, rain/no rain is determined for each angle bin, a flag is set up, and the rain height is calculated. Moreover, influence of surface clutter, which is mixed from antenna main lobe and side lobe, is evaluated, and the evaluation result is reflected to the calculation of surface range bin number and the determination of rain/no rain.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.