Comparison of Results of SAGE III Atmospheric Sounding with Data of Independent Interpretation, Measurements and Numerical Modeling Yu. M. Timofeyev*, A.V. Polyakov, A.M. Chaika Research Institute of Physics, St.-Petersburg State University, * Nansen International Environmental and Remote Sensing Center, St.Petersburg, Russia E. Rozanov(1,2), T. Egorova (2), M. Schraner (1), W. Schmutz (2) (1) Institute for Atmospheric and Climate Science, ETH, Zurich, Switzerland (2) PMOD/WRC, Davos, Switzerland Interpretation and Validation of SAGE III Measurements Retrieval of Aerosol Microphysics SAGE III device SAGE III (Stratospheric Aerosol and Gas Experiment III) [www- sage3.larc.nasa.gov] was launched onboard the Russian satellite "Meteor-3M" in 10th December 2001 from Baikonur and began to operate in 27th February SAGE III is a diffraction spectrophotometer with the CCD detector measuring the intensity of Sun radiation in the continuous range nm and at 1550 nm. Although SAGE III makes 809 individual spectral measurements, in practice only discrete values (a combination of one or more digitized CCD element measurements) are transmitted to the ground. Most channels are in gas absorption bands of measured gases. There are 9 aerosol channels: 1550, , 869, 755, 675, 601, 520, , 384 nm. Comparison and Validation 1. Climatology models 2. CRISTA I 3. HALOE 4. POAM III 5. SAGE III – operational 6. Ozonesondes 7. Lidar 8. Dust sondes 9. Numerical 3-D models Principal Features of SAGE III transmittance measurement interpretation 1) Optimal estimation algorithm extended to the non-linear problem [Polyakov, 1996]. 2) Simultaneous retrieval of vertical profiles of atmospheric gases and spectral-altitude behavior of aerosol extinction coefficient from measured transmittance data. 3) Optimal parameterization of the spectral dependence of aerosol extinction coefficient. 4) Careful consideration of spectral and angular device characteristics [Polyakov at al., 2005, 2005a]. 5) Determination of aerosol microphysics parameters using the multiple linear regression. A new algorithm has been independently developed for the retrieval of atmospheric gas concentrations and aerosol extinction from the SAGE III transmission data. This new algorithm differs from the NASA operational algorithm by several key aspects: - the algorithm takes into account the finite altitude and spectral resolution of measurements by integrating over the width of the viewing window spatially and spectrally; - the problem is solved non-linearly using the optimal estimation algorithm; - the algorithm uses the transmittance measurements, not optical density, as in operational NASA algorithm; - the aerosol extinction is parameterized by an optimal expansion using the eigenvectors of the aerosol extinction correlation matrix. This matrix was constructed via numerical simulation for a large database of models of stratospheric and tropospheric aerosol (see Timofeyev et al, 2003; Virolainen et al, 2004). Comparison of SPbSU and NASA operational algorithms Fig.5. Mean (solid curve) and RMS (dotted curve) differences. 200 measurements, Apr NASA retrievals: mesospheric - from measurements in Hartley-Huggins band, method MLR and Least Squares - from measurements in the Chappuis band. Below 45 km (excluding the altitude range km) SPbSU and NASA retrievals are well agreed (within 5-7% and 10% for Mean and RMS differences). At the km altitudes differences are about 20% on the average. Above 65 km differences increase to 50% and more. Fig.6. Relative mean (on the left) and RMS (on the right) differences between ozone retrievals by T- and D- algorithms, and ozonosonde data (with respect to the mean ozonosonde profile). [ Polyakov and Timofeyev, 2004] T-algorithm has apparent advantages at the altitudes below 12.5 km. Ozone retrieval and validation SAGE III, event ID , 07/28/02, 19:03, 46.63N, 7.21E; LIDAR, Hohenpasseberg. Distance km, 23 h Fig.1. Comparison of SPbSU, SAGE III and Lidar ozone profiles. Fig.2. Comparison of SPbSU ozone retrievals with POAM-III data. 50 measurements in Sept and March-April 2003, ~65N, 550 km distance and 15 minutes time shift. Fig.3. Comparison of SPbSU ozone retrievals with HALOE, SAGE III (level 2) and ozonosonde data. 45 ozonesonde profiles are used in the comparison. A new method for retrieving the atmospheric aerosol characteristics (in particular the total surface area S and volume V ) from AEC occultation measurements has been developed. In solving the inverse problem by the linear multiple regression method, the key aspect of the method is the use of a priori information on statistical relations between different aerosol optical characteristics (in the form of matrices for extinction and scattering coefficients, and scattering indicatrix). 1. Original method for interpreting the SAGE III (Sun occultation mode) data has been developed that makes it possible to retrieve simultaneously the following vertical profiles: ozone (10-90 km), NO 2 (10-40 km), the spectral aerosol extinction coefficient (AEC) (10-35 km), integral parameters of stratospheric aerosol microstructure (10-30 km). 2. Developed method has been tested by comparisons of retrievals with independent measurements by ozonosondes, lidars, aerosondes and other satellite devices (HALOE, POAM III, CRISTA). Disagreements are: 5-15% - for ozone, 20-40% - for NO 2, 10-50% - for AEC, % - for total surface and volume areas (depending on altitude and vertical resolution). 3. Comparison of data retrieved from SAGE III measurements by SPbSU and NASA operative methods has shown: · in the most part of the stratosphere both ozone retrievals agree within 5-7% and 10% for Mean and RMS differences, at the km altitudes differences are about 20% on the average, above 65 km differences increase to 50% and more; · NO 2 retrievals agree within 20-50% with the systematic difference of 10-20% in the range of stratospheric layer of this gas; · spectral AECs are in good agreement at 1  m, but the systematic difference equal to 30-50% is observed in the short-wave spectral range. 4. Retrieved aerosol parameters S and V show prominent seasonal and longitudinal variations (by 3-4 times). Conclusion Egorova T., E. Rozanov, V. Zubov, E. Manzini, W. Schmutz, and T. Peter, 2005: Chemistry-climate model SOCOL: a validation of the present-day climatology. ACPD, 5, SRef-ID: /acpd/ , Polyakov A.V., 1996: To the question of using statistical information, a priori, in solving nonlinear inversed problems of atmospheric optics. Earth Res. from Space, 3, 11–15 (Engl. transl.). Polyakov A.V., Yu.M. Timofeyev, 2004: Influence of the algorithm for solving the inverse problem on results of the atmospheric sounding by occultation method (SAGE III device). Earth Res. from Space, 5, (Engl. transl.). Polyakov A.V., Y.M. Timofeyev, D.V. Ionov, Y. A. Virolainen, H.M. Steele, M.J. Newchurch, 2005: Retrieval of ozone and nitrogen dioxide concentrations from Stratospheric Aerosol and Gas Experiment III (SAGE III) measurements using a new algorithm. J. Geophys. Res., 110, No. D6, D06303 Polyakov A.V., Yu.M. Timofeyev, D.V. Ionov et al., 2005a: New interpretation of transmittance measurements by SAGE III satellite spectrometer. Izv. RAS, Atm. and Ocean. Phys., 41, 3, 410–422 (Engl. transl.). Timofeyev Yu.M., A.V. Polyakov, H.M. Steele, M.J. Newchurch, 2003: Optimal Eigenanalysis for the Treatment of Aerosols in the Retrieval of Atmospheric Composition from Transmission Measurements. Appl. Opt., 42, 15, 2635  Virolainen Ya.A., A.V. Polyakov, Yu.M. Timofeyev, 2004: Statistical optical models of tropospheric aerosol. Izv. RAS, Atm. and Oceanic Phys., 40, 2, References The authors are grateful to P. DeCola, W. Chu and the SAGE III team for the experimental data and useful discussions and NASA Langley Research Center and Atmospheric Sciences Data Center for putting in their disposal the SAGE III (level 1b and 2) measurement data. This work was supported in part by NASA grant NAG and the Russian Foundation for Basic Research Projects and а. Acknowledgement Altitude, km S,  m 2 /cm 3 Fig.7. Comparison of S profiles retrieved from SAGE III measurements with aerosonde (Wyoming, USA) data. Validation of S retrievals Longitudinal S variability Fig.8. Longitudinal S variability retrieved from SAGE III measurements. Altitude step is 0.5 km. Black curve - aerosonde, , 41N 105W Green curve - SAGE III, , 50N 110W Red curve - SAGE III, , 50N 100W Blue curve  SAGE III, , 50N 109W Retrieved S fields Retrieved V fieldsComparison of S Fields for Two Years Comparison of retrieved and modeled ozone fields March 2003 Fig.4. Ozone fields: (1) retrieved from SAGE III, (2) modeled by SOCOL, (3) differences.