CALIBRATION OF THE MICROWAVE LIMB SOUNDER ON THE UPPER-ATMOSPHERE RESEARCH SATELLITE

The Microwave Limb Sounder (MLS) is a three-radiometer, passive, limb emission instrument onboard the Upper Atmosphere Research Satellite (U ARS). Radiometric, spectral and field-of-view calibrations of the MLS instrument are described in this paper. In-orbit noise performance, ga in stability, spectral baseline and dynamic range are described, as we ll as use of in-flight data for validation and refinement of prelaunch calibrations. Estimated systematic scaling uncertainties (3 sigma) on calibrated limb radiances from prelaunch calibrations are 2.6% in ban ds 1 through 3, 3.4% in band 4, and 6% in band 5. The observed systema tic errors in band 6 are similar to 15%, consistent with prelaunch cal ibration uncertainties. Random uncertainties on individual limb radian ce measurements are very close to the levels predicted from measured r adiometer noise temperature, with negligible contribution from noise a nd drifts on the regular in-flight gain calibration measurements.