Technical Note: Time-dependent limb-darkening calibration for solar occultation instruments S. P. Burton1,*, L. W. Thomason2, and J. M. Zawodny2 1SAIC, Hampton, Virginia, USA 2NASA Langley Research Center, Hampton, Virginia, USA *now at: Science Systems and Applications, Inc., Hampton, Virginia, USA
Abstract. 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. The technique is potentially useful for any scanning solar
occultation instrument and suggests further improvement for future
occultation measurements if a full disk imaging system can be included.
Citation: Burton, S. P., Thomason, L. W., and Zawodny, J. M.: Technical Note: Time-dependent limb-darkening calibration for solar occultation instruments, Atmos. Chem. Phys., 10, 1-8, doi:10.5194/acp-10-1-2010, 2010.