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 like ESMR provided the first observations of rain over the ocean via microwave radiometry. Later, Special Sensor Microwave/Imager (SSM/I) allowed for improved rainfall retrieval algorithms using multiple frequencies. Profiling algorithms were also developed to estimate rain rates from passive microwave measurements over both ocean and land.