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The UARS satellite orbited the Earth to collect atmospheric data.

As the first major element in NASA's Earth Science Enterprise (ESE) (formerly Mission to Planet Earth), the Upper Atmosphere Research Satellite (UARS) carried out the first systematic, comprehensive study of the stratosphere and furnished important new data on the mesosphere and thermosphere. The goal of the UARS was to understand the chemistry, dynamics, and energy balance above the troposphere, as well as the coupling between these processes and between regions of the atmosphere. The UARS platform provided near global (80° South to 80° North), simultaneous, coordinated measurements of atmospheric internal structure (trace constituents, physical dynamics, radiative emission, thermal structure, density) and measurements of the external influences acting upon the upper atmosphere (solar radiation, tropospheric conditions, electric fields).

UARS was launched in 1991 on a 3-year mission. UARS operated 585 km above the Earth in a near circular orbit inclined 57 degrees to the equator. This orbit permitted UARS sensors to view up to the 80-degree latitude bands providing essentially global coverage of the stratosphere and mesosphere. This also permitted the UARS instruments to make measurements over the full range of local times at all geographic locations approximately every 36 days. The UARS mission came to an end in September 2001 after 10 years of service. The last shipment of data was in November (9/17/2001).

UARS carried 10 science instruments uniquely designed to provide data with unprecedented precision, quality, and scope. Data from these instruments will be processed into continuous long-term measures concerned with the upper atmosphere. The following 10 instruments were on board UARS:

• Cryogenic Limb Array Etalon Spectrometer (CLAES), measured temperature profiles and concentrations of ozone, methane, water vapor, nitrogen oxides, and other important species, including CFCs, in the stratosphere.
• Improved Stratospheric and Mesospheric Sounder (ISAMS), a limb-sounding radiometer, used a combination of pressure-modulated and wide-band infrared channels to measure carbon monoxide, water vapour, nitrogen dioxide, nitric acid, ozone, nitric xxide, nitrous oxide, methane, dinitrogen pentoxide, aerosol, and temperature in the middle atmosphere.
• Microwave Limb Sounder (MLS) measured naturally-occurring microwave thermal emission from the limb of Earth's atmosphere to remotely sense vertical profiles of selected atmospheric gases, temperature, and pressure.
• Halogen Occultation Experiment (HALOE) solar occultation to measure vertical profiles of ozone, hydrogen chloride, hydrogen fluoride, methane, water, nitric oxide, nitrogen dioxide, aerosol extinction, aerosol surface, and temperature.
• High Resolution Doppler Imager (HRDI) observed the emission and absorption lines of molecular oxygen (and other atmospheric components) and determins wind properties from the Doppler shift.
• Wind Imaging Interferometer (WINDII) measured wind, temperature, and emission rate over the altitude range from 80 to 300 km by using the visible region airglow emission from these altitudes.
• Solar-Stellar Irradiance Comparison Experiment (SOLSTICE) provided long-term, accurate measurements of the solar ultraviolet (UV) and far ultraviolet (FUV) radiation.
• Solar Ultraviolet Spectral Irradiance Monitor (SUSIM) measured the absolute irradiance of the UV light in the wavelength range 115 to 410 nm.
• Particle Environment Monitor (PEM), provided quantitative measurements of both local and global energy inputs into the Earth's atmosphere by charged particles, x-rays, and the magnetic field.
• Active Cavity Radiometer Irradiance Monitor (ACRIM II), an instrument of opportunity, measured the total radiant energy from the Sun.