The TIROS Operational Vertical Sounder (TOVS) was developed as part of the Television Infrared Observation Satellite (TIROS) program. TOVS measured vertical profiles of atmospheric humidity, temperature, and ozone, and monitored clouds and radiation on a global scale.

TIROS was NASA's first major initiative to develop satellite remote sensing for Earth observations, beginning with the launch of TIROS-1 in 1962. TIROS began before satellite remote sensing had become well-established, and provided an important opportunity for improving satellite design and operational parameters. 

TOVS was first launched in 1978 on the TIROS-N/NOAA satellite, and is a system of three sensors: the Stratospheric Sounding Unit (SSU); the High Resolution Infrared Radiation Sounder 2 (HIRS/2); and the Microwave Sounding Unit (MSU). TOVS instruments continue to be carried aboard NOAA meteorological satellites, and are still providing atmospheric and climate data.