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The Earth Observing System Microwave Limb Sounder measures several atmospheric chemical species (OH, H[O.sub.2], [H.sub.2]O, [O.sub.3], HCl, ClO, HOCl, BrO, HN[O.sub.3], [N.sub.2]O, CO, HCN, C[H.sub.3] CN, volcanic S[O.sub.2]), cloud ice, temperature, and geopotential height to improve our understanding of stratospheric ozone chemistry, the interaction of composition and climate, and pollution in the upper troposphere. All measurements are made simultaneously and continuously, during both day and night. The instrument uses heterodyne radiometers that observe thermal emission from the atmospheric limb in broad spectral regions centered near 118, 190, 240, and 640 GHz, and 2.5 THz. It was launched July 15, 2004 on the National Aeronautics and Space Administration's Aura satellite and started full-up science operations on August 13, 2004. An atmospheric limb scan and radiometric calibration for all bands are performed routinely every 25 s. Vertical profiles are retrieved every 165 km along the suborbital track, covering 82[degrees]S to 82[degrees]N latitudes on each orbit. Instrument performance to date has been excellent; data have been made publicly available; and initial science results have been obtained. Index Terms--Microwave, remote sensing, stratosphere, submillimeter wave.

In September 1991, NASA launched the Upper Atmosphere Research Satellite (UARS). In addition to its atmospheric science mission, spacecraft dynamic effects on science measurements were analyzed. The investigation included two in-flight experiments to determine how each onboard instrument, subsystem, and environmental disturbance contributed to the spacecraft dynamic response and how these disturbances affected science measurements. Three case studies are presented that show the impact of spacecraft dynamic response on science measurements. The case studies have demonstrated that the influence of spacecraft dynamic response needs to be examined in most remote-sensing spacecraft that have attitude jitter levels commensurate to instrument pointing requirements. In the first case, correlation of independent atmospheric meridional wind measurements taken by two instruments with the spacecraft dynamic response demonstrated that excessive vibration (exceeding instrument pointing requirements) resulted in wind measurement disagreement. In the second case, solar array disturbances produced a spacecraft response signature on radiometer measurements. The signature explicitly demonstrated that if an instrument has sufficient spatial and temporal resolution, spacecraft dynamic response could impact measurements. In the final case, correlation of an instruments fine sun-sensor data and C[O.sub.2] measurements demonstrated the effect of temporal and spatial sampling resolution and active pointing control on science measurements. The sun sensor had a frequency modulated characteristic, due to spacecraft vibration and the periodic scanning of another instrument, which was not present on the C[O.sub.2] measurements. Index Terms - Atmospheric measurements, Halogen Occultation Experiment (HALOE), High Resolution Doppler Image (HRDI), jitter, Microwave Limb Sounder (MLS), spacecraft dynamic response, Upper Atmosphere Research Satellite (UARS), vibration, Wind Imaging Interferometer (WINDII).