NASA Logo, National Aeronautics and Space Administration
NASA Space Science Data Coordinated Archive Header

TIROS Operational Vertical Sounder (TOVS)

NSSDCA ID: 1993-050A-02

Mission Name: NOAA 13
Principal Investigators:Dr. Joel Susskind
Principal Investigators:


The TIROS Operational Vertical Sounder (TOVS) on NOAA-I consisted of three instruments: the High-resolution Infrared Radiation Sounder modification 2 (HIRS/2), the Stratospheric Sounding Unit (SSU), and the Microwave Sounding Unit (MSU). All three instruments were designed to determine radiances needed to calculate temperature and humidity profiles of the atmosphere from the surface to the stratosphere (approximately 1 mb). The HIRS/2 instrument had 20 channels in the following spectral intervals: channels 1 through 5, the 15-micrometer CO2 bands (15.0, 14.7, 14.5, 14.2, and 14.0 micrometers); channels 6 and 7, the 13.7 and 13.4-micrometer CO2/H2O bands; channel 8, the 11.1-micrometer window region; channel 9, the 9.7-micrometer ozone band; channels 10 through 12, the 6-micrometer water vapor bands (12.55, 7.3, and 6.7 micrometers); channels 13 and 14, the 4.57- and 4.52-micrometer N2O bands; channels 15 and 16, the 4.46- and 4.40-micrometer CO2/N2O bands; channels 17, 18 and 19, the 4.25-, 4.0- and 3.7-micrometer window bands; and channel 20, the 0.7-micrometer visible region. For NOAA-I AND -J, channel 10 and 17 operated at 12.25 and 4.13 micrometers, respectively. Resolution for all channels was 17.4 km at nadir. The HIRS/2 instrument provided data for calculations of temperature profiles from the surface to 10 mb, water vapor content at three levels of the atmosphere, and total ozone content. HIRS/2 was made up of a scan system, optics, radiant cooler and detectors, electronics and data handling, and mechanical systems. The HIRS/2 scan mirror was stepped in synch with the spacecraft clock. The mirror was stepped in 1.8 degree steps acquiring data at 56 data points. The optical system consisted of two field stops: one for longwave and another for shortwave radiation. The instrument bandpass was defined by filters located on a filter wheel behind each field stop. A relay lens system focused the radiation on the detectors. The radiant cooler maintained temperature control for the thermal channels. The second instrument, the SSU, was provided by United Kingdom. The SSU measured temperature profiles in the upper atmosphere from 25 to 50 km in altitude. It had three channels that operated at 669.99, 669.63, and 669.36 per cm using three pressure-modulated cells containing CO2 (at 100, 35 and 10 mb) to accomplish selective bandpass filtration of the sampled radiance. The SSU consisted of a single telescope with a 10 degree IFOV that was step scanned perpendicular to the subpoint track. Each scan line was composed of 8 individual 4 second steps. The SSU used uncooled pyroelectric detectors that integrated the radiance in each channel for 3.6 seconds during each step. A single 8-cm scan mirror was used for all three channels. The SSU detector was a flake of tri-glycine sulphate attached to the end of a conical gold-plated nickel pipe. The exit aperature of the pipe defined the illuminated area on the flake, and the input end of the pipe defined the FOV. The three detectors were mounted on a common block. The SSU was calibrated in synchonism with HIRS/2 once every 8 scans. The third instrument, the MSU, had four channels operating in the 50- to 60-GHz oxygen band (50.31, 53.73, 54.96 and 57.95 GHz) which obtained vertical temperature profiles free of cloud interference to an altitude of about 20 km. The MSU, developed by JPL, was a 4-channel Dicke radiometer and consisted of two scanning reflector antenna systems, orthomode transducers, four Dicke receivers, data programmer, and power supplies. The antennas scanned 47.4 degrees on either side in 11 steps. Microwave energy received by each antenna was separated into vertical and horizontal polarization components by an orthomode transducer and each of the four signals was fed into one of the radiometer channels. The MSU was used along with HIRS/2 to remove data ambiguities caused by clouds.

Alternate Names

  • TOVS

Funding Agencies

  • NASA-Office of Space Science Applications (United States)
  • NOAA National Environmental Satellite Service (United States)


  • Earth Science: Atmospheric Dynamics

Additional Information

Questions and comments about this experiment can be directed to: Coordinated Request and User Support Office



NameRoleOriginal AffiliationE-mail
Principal InvestigatorNOAA National Environmental Satellite, Data and Information Service
Dr. Joel SusskindTeam LeaderNASA Goddard Space Flight
[] NASA Logo -