WWC snapshot of http://pegasus.nesdis.noaa.gov/tovs.html taken on Sat May 6 16:36:51 1995

U.S. Department of Commerce

National Oceanic and Atmospheric Administration

                     NOAA Operational Environmental Satellites

NOAA Polar-Orbiting Operational Environmental Satellite (POES)

TIROS Operational Vertical Sounder (TOVS)

The TIROS-N series of Earth observing satellites has provided a near continuous record of operational vertical sounder radiance data from 19 October, 1978 to the present. The TIROS platforms, designed to operate in a near-polar, sun-synchronous orbit with an orbital period of approximately 102 minutes, produce 14.1 orbits per day. Because the number of orbits per day is not an integer, the sub-orbital tracks do not repeat on a daily basis. The local solar time of the satellite's passage, however, is essentially unchanged for any given latitude.

The TOVS system consists of three instruments: the HIRS/2I, the SSU, and the MSU. All three instruments measure radiant energy from various altitudes of the atmosphere and the data are used to determine the atmosphere's temperature from the Earth's surface to the upper stratosphere.

High Resolution Infrared Radiation Sounder (HIRS/2I)

This instrument detects and measures energy emitted by the atmosphere to construct a vertical temperature profile from the Earth's surface to an altitude of about 40 km. Measurements are made in 20 spectral regions in the infrared band. Note that one frequency lies at the high frequency end of the visible range.

Stratospheric Sounding Unit (SSU)

Temperature measurements from the upper stratosphere are derived from radiance measurements made in three channels using a pressure modulated gas (CO2) to accomplish selective bandpass filtrations of the sampled radiances. The gas is of a pressure chosen to yield weighting functions peaking in the altitude range of 25 to 50 km where atmospheric pressure is from 15.1 to 1.5 mbar respectively. This gas is contained in three cells, one of which is located in the optical path of each channel.

Microwave Sounding Unit (MSU)

This unit detects and measures the energy from the troposphere to construct a vertical temperature profile to an altitude of about 20 km. Measurements are made by radiometric detection of microwave energy divided into four frequency channels. Each measurement is made by comparing the incoming signal from the troposphere with the ambient temperature reference load. Because its data are not seriously affected by clouds, the unit is used along with the HIRS/2I to remove measurement ambiguity when clouds are present.

NOAA Polar Orbiter Data Users Guide

For a comprehensive description of the NOAA Polar-orbiting Operational Environmental Satellites, click HERE to view the on-line users guide.

Peter J. Topoly (ptopoly@nesdis.noaa.gov) 3/16/95