Odin-OSIRIS stratospheric aerosol data product and SAGE III intercomparison

摘要

The scattered sunlight measurements made by the Optical Spectrograph andInfraRed Imaging System (OSIRIS) on the Odin spacecraft are used to retrievevertical profiles of stratospheric aerosol extinction at 750 nm. Therecently released OSIRIS Version 5 data product contains the first publiclyreleased stratospheric aerosol extinction retrievals, and these are nowavailable for the entire Odin mission, which extends from the present dayback to launch in 2001. A proof-of-concept study for the retrieval ofstratospheric aerosol extinction from limb scatter measurements waspreviously published and the Version 5 data product retrievals are based onthis work, but incorporate several important improvements to the algorithm.One of the primary changes is the use of a new retrieval vector that greatlyimproves the sensitivity to aerosol scattering by incorporating a forwardmodeled calculation of the radiance from a Rayleigh atmosphere. Additionalimprovements include a coupled retrieval of the effective albedo, a newmethod for normalization of the retrieval vector to improve signal-to-noise,and the use of an initial guess that is representative of very low backgroundaerosol loading conditions, which allows for maximal retrieval range.Furthermore, the Version 5 data set is compared to Stratospheric Aerosol andGas Experiment (SAGE) III 755 nm extinction profiles during the almost fouryears of mission overlap from 2002 to late 2005. The vertical structure incoincident profile measurements is well correlated and the statistics on arelatively large set of tight coincident measurements show agreement betweenthe measurements from the two instruments to within approximately 10%throughout the 15 to 25 km altitude range, which covers the bulk of thestratospheric aerosol layer for the mid and high latitude cases studied here.