Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 9 5 2009 10.5194/acpd-9-20259-2009 http://www.atmos-chem-phys-discuss.net/9/20259/2009/ http://www.atmos-chem-phys-discuss.net/9/20259/2009/acpd-9-20259-2009.html http://www.atmos-chem-phys-discuss.net/9/20259/2009/acpd-9-20259-2009.pdf 20259 20282 2009-09-28 Technical Note: A time-dependent calibration correction for solar occultation instruments S. P. Burton sharon.p.burton@nasa.gov L. W. Thomason J. M. Zawodny SAIC, Hampton, Virginia, USA NASA Langley Research Center, Hampton, Virginia, USA now at: Science Systems and Applications, Inc., Hampton, Virginia, USA Solar occultation has proven to be a reliable technique for the measurement of atmospheric constituents in the stratosphere. NASA's Stratospheric Aerosol and Gas Experiments (SAGE, SAGE II, and SAGE III) together have provided over 25 years of quality solar occultation data, a data record which has been an important resource for the scientific exploration of atmospheric composition and climate change. Herein, we describe an improvement to the processing of SAGE data that corrects for a previously uncorrected short-term time-dependence in the calibration function. The variability relates to the apparent rotation of the scanning track with respect to the face of the sun due to the motion of the satellite. Correcting for this effect results in a decrease in the measurement noise in the Level 1 line-of-sight optical depth measurements of approximately 40% in the middle and upper stratospheric SAGE II and III observations where it has been applied. 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