The<i>UARS</i>and EOS Microwave Limb Sounder (MLS) Experiments

TLDR

The Microwave Limb Sounder (MLS) obtains global, high‑resolution measurements of atmospheric composition, temperature, and pressure by scanning limb thermal emission, enabling accurate profiling of gases such as ClO, O3, and H2O even in aerosol, with stable calibration and a comprehensive spectroscopic database, and its first spaceflight on UARS in 1991 established this capability. The UARS MLS was designed to globally measure ClO, the key radical in ozone depletion, while the EOS MLS is being developed to extend stratospheric measurements to HOx radicals and improve upper‑tropospheric and lower‑stratospheric coverage. EOS MLS will employ advanced instrumentation to capture HOx radicals and deliver higher‑resolution upper‑tropospheric and lower‑stratospheric profiles beyond UARS capabilities. UARS MLS achieved all its objectives and produced additional products such as upper‑tropospheric water vapor measurements that are important for climate change studies.

Abstract

The Microwave Limb Sounder (MLS) experiments obtain measurements of atmospheric composition, temperature, and pressure by observations of millimeter- and submillimeter-wavelength thermal emission as the instrument field of view is scanned through the atmospheric limb. Features of the measurement technique include the ability to measure many atmospheric gases as well as temperature and pressure, to obtain measurements even in the presence of dense aerosol and cirrus, and to provide near-global coverage on a daily basis at all times of day and night from an orbiting platform. The composition measurements are relatively insensitive to uncertainties in atmospheric temperature. An accurate spectroscopic database is available, and the instrument calibration is also very accurate and stable. The first MLS experiment in space, launched on the (NASA) Upper Atmosphere Research Satellite (UARS) in September 1991, was designed primarily to measure stratospheric profiles of ClO, O3, H2O, and atmospheric pressure as a vertical reference. Global measurement of ClO, the predominant radical in chlorine destruction of ozone, was an especially important objective of UARS MLS. All objectives of UARS MLS have been accomplished and additional geophysical products beyond those for which the experiment was designed have been obtained, including measurement of upper-tropospheric water vapor, which is important for climate change studies. A follow-on MLS experiment is being developed for NASA’s Earth Observing System (EOS) and is scheduled to be launched on the EOS CHEMISTRY platform in late 2002. EOS MLS is designed for many stratospheric measurements, including HOx radicals, which could not be measured by UARS because adequate technology was not available, and better and more extensive upper-tropospheric and lower-stratospheric measurements.