The Upper Atmosphere Research Satellite microwave limb sounder instrument

Abstract

The microwave limb sounder (MLS) on the Upper Atmosphere Research Satellite (UARS) is the first satellite experiment using limb sounding techniques at microwave frequencies. Primary measurement objectives are stratospheric ClO, O3, H2O, temperature, and pressure. Measurements are of thermal emission: all are performed simultaneously and continuously and are not degraded by ice clouds or volcanic aerosols. The instrument has a 1.6‐m mechanically scanning antenna system and contains heterodyne radiometers in spectral bands centered near 63, 183, and 205 GHz. The radiometers operate at ambient temperature and use Schottky‐diode mixers with local oscillators derived from phase‐locked Gunn oscillators. Frequency tripling by varactor multipliers generates the 183‐ and 205‐GHz local oscillators, and quasi‐optical techniques inject these into the mixers. Six 15‐channel filter banks spectrally resolve stratospheric thermal emission lines and produce an output spectrum every 2 s. Thermal stability is sufficient for “total power” measurements which do not require fast chopping. Radiometric calibration, consisting of measurements of cold space and an internal target, is performed every 65‐s limb scan. Instrument in‐orbit performance has been excellent, and all objectives are being met.

Observations of the mesospheric semi-annual oscillation (MSAO) in water vapour by Odin/SMR

“…The stratospheric SAO in water vapour has for example been observed by the MLS -Microwave Limb Sounder, Barath et al (1993), and the HALOE -Halogen Occultation Experiment, Russell et al (1993), instrument, both aboard the Upper Atmosphere Research Satellite (UARS) (Carr et al, 1995;Randel et al, 1998;Jackson et al, 1998). Signatures of the stratospheric SAO could be observed above 20 hPa (∼27 km).…”

Past changes in the vertical distribution of ozone – Part 1: Measurement techniques, uncertainties and availability

“…2). UARS-MLS (a predecessor to Aura MLS) pioneered microwave limb sounding of the Earth's stratosphere and mesosphere from space (see Barath et al, 1993;Waters, 1993). UARS-MLS measured microwave emission near 205 GHz for its primary stratospheric ozone retrievals.…”

Evaluation of wind and temperature profiles from ECMWF analysis on two hemispheres using volcanic infrasound

“…Apart from operational weather satellites, valuable observations have been obtained during satellite measurement campaigns. Examples of research instruments include the High Resolution Doppler Imager [Hays et al, 1993] and the Microwave Limb Sounder [Barath et al, 1993] onboard NASA's Upper Atmosphere Research Satellite (UARS) that measured from 1991 to 2005. Temperature is measured indirectly through radiance; this measure also provides information on humidity and ozone.…”