SCIAMACHY Offline Processor Level1b-2 ATBD Algorithm Theoretical Baseline Document (SGP OL Version 7) Issue 3 prepared institute date signature G. Lichtenberg, S. DLR-IMF 16.04.18 Hrechanyy checked SQWG copies to ESA Contents I. Introduction9 1. About this document 10 1.1. Purpose and scope............................................ 10 1.2. Historical Background.......................................... 10 1.3. Acronyms and Abbreviations...................................... 10 1.4. Document Overview........................................... 11 2. The Data Processor 12 2.1. Processing flow overview........................................ 12 2.2. Components of the Data Processor................................... 12 2.2.1. Database Server......................................... 13 2.2.2. Nadir Retrieval Server...................................... 13 2.2.3. Limb Retrieval Server...................................... 13 2.3. Overview of MDS............................................. 13 II. Nadir Retrieval Algorithms 14 3. Cloud Parameters 15 3.1. Cloud Top Height and Cloud Optical Thickness............................ 15 3.1.1. Overview............................................. 15 3.1.2. Detailed Description....................................... 15 3.1.2.1. Cloud Top Height................................... 15 3.1.2.2. Cloud Optical Thickness............................... 16 3.2. Cloud Fraction.............................................. 17 3.2.1. Introduction............................................ 17 3.2.2. Generation of the cloud-free composite............................ 18 3.2.3. Determination of the cloud fraction............................... 19 3.2.4. Future improvements...................................... 19 4. Absorbing Aerosol Index 20 4.1. Overview................................................. 20 4.1.1. Retrieval Settings........................................ 20 4.2. Detailed Description........................................... 20 4.2.1. Definition of used geometry................................... 20 4.2.2. Definition of the Residue.................................... 21 4.2.3. Definition of the AAI....................................... 21 4.2.4. Calculation of the Residue................................... 22 4.2.5. Look-up Tables.......................................... 22 4.2.6. Degradation Correction..................................... 22 5. SDOAS Algorithm General Description 24 5.1. Slant column retrieval.......................................... 24 5.2. Vertical column retrieval......................................... 25 5.3. Nadir Ozone Total Column Retrieval.................................. 26 5.3.1. Motivation............................................. 26 5.3.2. Retrieval Settings........................................ 27 1 Docnr.: ENV-ATB-QWG-SCIA-0085 Issue : 3 Date : 16.04.18 5.3.3. Additional Details......................................... 27 5.3.3.1. Molecular Ring correction............................... 27 5.3.3.2. Vertical column with iterative approach....................... 28 5.4. Nadir NO2 Total Column Retrieval................................... 29 5.4.1. Motivation............................................. 29 5.4.2. Retrieval Settings........................................ 29 5.5. Nadir SO2 Total Column Retrieval.................................... 30 5.5.1. Retrieval Settings........................................ 30 5.5.2. Additional Details......................................... 30 5.5.2.1. Slant Column...................................... 30 5.5.2.2. Vertical Column.................................... 31 5.6. Nadir BrO Total Column Retrieval.................................... 32 5.6.1. Motivation............................................. 32 5.6.2. Retrieval Settings........................................ 32 5.7. Nadir OClO Slant Column Retrieval................................... 33 5.7.1. Retrieval Settings........................................ 33 5.7.2. Additional Details......................................... 33 5.8. Nadir HCHO Total Column Retrieval.................................. 33 5.8.1. Motivation............................................. 33 5.8.2. Retrieval Settings........................................ 34 5.8.3. Additional Details......................................... 34 5.8.4. User warning........................................... 35 5.9. Nadir CHOCHO Total Column Retrieval................................ 35 5.9.1. Retrieval Settings........................................ 35 5.9.2. Additional Details......................................... 36 5.9.3. User warning........................................... 36 6. Water Vapour Retrieval 37 6.1. Inversion Algorithm............................................ 37 6.2. Forward Model and Databases..................................... 39 6.3. Auxiliary Data............................................... 39 7. Infra-red Retrieval using BIRRA 40 7.1. Introduction................................................ 40 7.1.1. A first glimpse at near IR nadir observations.......................... 40 7.2. Forward Modelling............................................ 43 7.2.1. Radiative Transfer........................................ 43 7.2.1.1. General Considerations: Schwarzschild and Beer................. 43 7.2.1.2. Radiative transfer modelling of nadir near infra-red observations......... 43 7.2.2. Molecular Absorption...................................... 44 7.2.2.1. Line strength and partition functions......................... 44 7.2.2.2. Line broadening.................................... 45 7.2.3. Geometry............................................. 48 7.2.3.1. Uplooking........................................ 48 7.2.3.2. Downlooking...................................... 49 7.2.3.3. Refraction....................................... 50 7.2.4. Instrument - Spectral Response................................ 51 7.2.5. Input data for forward model................................... 52 7.3. Inversion................................................. 55 7.3.1. Non-linear least squares..................................... 55 7.3.2. Separable non-linear least squares............................... 55 7.4. CO Retrieval............................................... 56 7.4.1. Detailed Description....................................... 56 7.4.2. Retrival Settings......................................... 57 7.5. CH4 Retrieval............................................... 57 7.5.1. Detailed Description....................................... 57 SGP OL1b-2 ATBD Version 7 Page 2 of 137 Docnr.: ENV-ATB-QWG-SCIA-0085 Issue : 3 Date : 16.04.18 7.5.2. Retrieval Settings........................................ 57 III. Limb Retrieval Algorithms 58 8. Limb Algorithm General Description 59 8.1. Summary of Retrieval Steps....................................... 59 8.2. Forward model radiative transfer.................................... 59 8.2.1. General considerations..................................... 59 8.2.2. Geometry of the scattering problem.............................. 61 8.2.3. Optical properties........................................ 67 8.2.3.1. Partial columns.................................... 67 8.2.3.2. Number density and VMR............................... 68 8.2.3.3. Scattering optical depth of air molecules...................... 68 8.2.3.4. Absorption optical depth of gas molecules..................... 69 8.2.3.5. Scattering optical depth of aerosols......................... 69 8.2.3.6. Total extinction optical depth............................. 69 8.2.3.7. Phase functions.................................... 70 8.2.4. Recurrence relation for limb radiance and Jacobian...................... 71 8.2.4.1. Recurrence relation for limb radiance........................ 72 8.2.4.2. Recurrence relation for the Jacobian matrix..................... 74 8.2.4.3. Input parameters for limb radiance and Jacobian calculation........... 77 8.2.5. Pseudo-spherical discrete ordinate radiative transfer equation................ 78 8.2.5.1. Requirement for a pseudo-spherical model..................... 78 8.2.5.2. General considerations................................ 79 8.2.5.3. Integral form of the layer equation.......................... 80 8.2.5.4. Layer equation..................................... 81 8.2.5.5. Matrix eigenvalue method............................... 81 8.2.5.6. Padé approximation.................................. 84 8.2.5.7. System matrix of the entire atmosphere....................... 85 8.2.5.8. Weighting functions calculation............................ 86 8.2.6. Picard iteration.......................................... 89 8.3. Inversion methods............................................ 92 8.3.1. Tikhonov regularization..................................... 93 8.3.1.1. Inversion models.................................... 93 8.3.1.2. Optimization methods for the Tikhonov function.................. 94 8.3.1.3. Practical methods for computing the new iterate.................. 100 8.3.1.4. Error characterisation................................. 103 8.3.1.5. Parameter choice methods.............................. 108 8.4. Relation Number Density and VMR.................................. 112 8.5. Common Characteristics of the Profile retrieval............................ 114 8.6. Limb Ozone Profile Retrieval Settings................................. 115 8.7. Limb NO2 Profile Retrieval Settings................................... 115 8.8. Limb BrO Profile Retrieval Settings..................................