Technical Note: Time-dependent limb-darkening calibration for solar occultation instruments

摘要

Solar occultation has proven to be a reliable technique for the measurementof atmospheric constituents in the stratosphere. NASA's StratosphericAerosol and Gas Experiments (SAGE, SAGE II, and SAGE III) together haveprovided over 25 years of quality solar occultation data, a data recordwhich has been an important resource for the scientific exploration ofatmospheric composition and climate change. Herein, we describe animprovement to the processing of SAGE data that corrects for a previouslyuncorrected short-term time-dependence in the calibration function. Thevariability relates to the apparent rotation of the scanning track withrespect 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 inthe 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 beenapplied. The technique is potentially useful for any scanning solaroccultation instrument and suggests further improvement for futureoccultation measurements if a full disk imaging system can be included.