The document discusses spaceborne microwave observations of rain from 1972 to 1997, beginning with the launch of the Electrically Scanned Microwave Radiometer (ESMR) on Nimbus 5 and concluding with the launch of the Tropical Rainfall Measuring Mission (TRMM). Early instruments provided the first observations of rain over the ocean but quantitative retrievals were limited. The Special Sensor Microwave/Imager (SSM/I) improved rainfall estimates with additional channels and calibration. Profiling algorithms were developed to retrieve rain rates from passive microwave measurements over ocean. TRMM introduced the first spaceborne precipitation radar to further advance quantitative rainfall measurements from space.