This study describes a calculation of the brightness temperature obtained from the spaceborne precipitation radar to utilize possible uses of precipitation estimates. Since the radar viewed from space measures emission and scattering signals from the earth, the brightness temperature at the radar's frequency is obtained from the noise power measured by the radar. The measurement accuracy of the radar's brightness temperature is also computed from the signal characteristics of the noise power. This study analyzes the noise power data of the Dual-frequency precipitation radar (DPR), whose frequency is at 13.6 and 35.5 GHz, onboard the Global Precipitation Measurement mission's (GPM's) core satellite. The calibrated brightness temperature data obtained from the DPR show the regional gradient between ocean and land surfaces and the emission signal from precipitation even if the measurement accuracy of the radar's brightness temperature is about 30 (50) K for the Ku-band (Ka-band) channel.