SCIAMACHY L0-1c Processor ATBD Algorithm Theoretical Baseline Document for Processor V.9 Issue 7A prepared Institute Date Signature S. SLijkhuis/G. Lichtenberg DLR-IMF February 7, 2019 checked SQWG copies to SQWG ESA Contents 1. Introduction 9 1.1. Overview of the SCIAMACHY mission.................................9 1.2. Purpose and scope............................................9 1.3. Document Overview........................................... 10 1.4. Document Status and History...................................... 10 1.5. Abbreviations and Acronyms...................................... 11 1.6. Applicable Documents.......................................... 13 2. SCIAMACHY Background Information and Algorithms Overview 14 2.1. Introduction to mission and data processing.............................. 14 2.1.1. Processing Requirements.................................... 14 2.1.2. Inheritance: relation to the GOME Data Processor...................... 14 2.2. SCIAMACHY Instrument Characteristics................................ 15 2.2.1. Instrument Hardware....................................... 15 2.2.2. Instrument Operation and Data Packet structure....................... 16 2.2.3. Instrument Calibration requirements for Level 0 to 1c processing.............. 18 2.3. The generic calibration equation.................................... 18 2.4. Determination of Calibration Parameters................................ 20 2.4.1. Overview............................................. 20 2.4.2. Onground Calibration...................................... 20 2.4.3. M-factors............................................. 20 2.4.4. Level 0 to 1b Processing of Calibration Constants...................... 21 2.5. Operational aspects of Level 0 to 1c processing............................ 22 2.6. Algorithms Overview........................................... 24 3. Level 0 to 1c Algorithms Description 27 3.1. Pre-processing of Mueller Matrix elements .............................. 27 3.1.1. Introduction to Mueller Matrix elements............................ 27 3.1.2. Rationale............................................. 29 3.1.3. Conversion of Key Data for polarisation sensitivity...................... 29 3.1.4. Conversion of Key Data for radiance sensitivity........................ 29 3.1.5. Calculation of Instrument Response.............................. 29 3.1.5.1. Generic Mueller Matrix and Contamination Layers................. 32 3.1.5.2. Phase Shift....................................... 33 3.1.5.3. Scanner Mueller Matrices............................... 34 3.1.6. Calculation of errors on Mueller matrix elements....................... 35 3.1.6.1. Errors for radiance response parameters...................... 35 3.1.6.2. Errors for polarisation sensitivity parameters.................... 36 3.2. Calculate Geolocation and Synchronise PMDs............................ 37 3.2.1. Determine integration time grid................................. 37 3.2.2. Integrated PMD values..................................... 39 3.2.3. Extract Line of Sight....................................... 40 3.2.3.1. Extraction of scan mirror positions.......................... 41 3.2.3.2. Calculation of the effective scan angle........................ 42 3.2.3.3. Conversion to the ILOS angles at Satellite..................... 43 3.2.4. Calculate geolocation...................................... 43 3.2.5. Conversion to TOA angles.................................... 45 3.2.6. Calculate Doppler shift...................................... 46 2 Docnr.: ENV-ATB-DLR-SCIA-0041 Issue : 7A Date : February 7, 2019 3.2.7. Determine SAA region...................................... 47 3.2.8. Calculate orbit phase...................................... 47 3.3. Correct Detector Readout Memory and Non-Linearity........................ 47 3.3.1. Calculation if no previous measurement available....................... 49 3.3.2. Scaling with PMDs at co-adding for memory effect...................... 50 3.3.3. Scaling with PMDs at co-adding for non-linearity....................... 51 3.4. Calculate Dark Signal.......................................... 53 3.4.1. Introduction............................................ 53 3.4.2. Calculation of FPN and LC from dedicated ‘Dark’ measurements.............. 53 3.4.3. Operational aspects....................................... 55 3.4.4. Modelling of LC over the orbit.................................. 56 3.4.5. Calculation of Solar Stray light from dedicated ‘Dark’ measurements............ 57 3.4.6. Quality check on Dark Signal using Limb States....................... 58 3.4.7. Dark Signal Correction for Channel 8.............................. 60 3.5. Apply Dark Signal............................................ 60 3.6. Calculate PPG and Etalon Parameters................................. 63 3.6.1. Introduction............................................ 63 3.6.2. Operational aspects....................................... 63 3.6.3. WLS preprocessing....................................... 64 3.6.4. Calculate Etalon......................................... 65 3.6.5. Calculate PPG.......................................... 67 3.6.6. Calculate the Dead & Bad Pixel Mask............................. 68 3.6.6.1. Channels 1-7...................................... 68 3.6.6.2. Channel 8....................................... 69 3.7. Apply PPG and Etalon Parameters................................... 70 3.8. Calculate Spectral Calibration Parameters............................... 71 3.8.1. Using Fraunhofer lines...................................... 73 3.8.2. Additional quality control parameters.............................. 74 3.8.3. Doppler shifts........................................... 74 3.9. Apply Spectral Calibration Parameters................................. 75 3.10.Determine Spectral Stray light...................................... 76 3.10.1. Uniform stray light........................................ 76 3.10.2. Ghost stray light......................................... 77 3.10.3. Channel 1 stray light....................................... 79 3.10.4. Stray light parameters on the Level 1b product........................ 79 3.11.Apply Stray light Correction....................................... 80 3.12.Apply BSDF and calculate SMR.................................... 81 3.12.1. Introduction............................................ 81 3.12.2. Solar Mean Reference spectrum from Sun diffuser measurements............. 82 3.12.3. Solar Mean Reference spectrum from other measurements................. 83 3.12.4. Calculation of average PMD signals.............................. 83 3.12.5. Calculation of out-of-band PMD signal............................. 84 3.12.6. Calculation of the Doppler-shift at 500 nm........................... 84 3.13.Determine Fractional Polarisation Values................................ 85 3.13.1. Introduction to polarisation measurements........................... 85 3.13.2. The theoretical point near 300 nm............................... 91 3.13.3. Polarisation Fractions from PMDs............................... 93 3.13.4. Determination of Polarisation Fractions in the UV for Limb.................. 96 3.13.5. Determination of the GDF parameters with CHEOPS..................... 97 3.13.6. Polarisation Correction Factor.................................. 98 3.13.7. Polarisation fractions from channel overlaps.......................... 98 3.14.Wavelength interpolation of polarisation values............................ 103 3.14.1. Introduction............................................ 103 3.14.2. Interpolation - default case with all points available...................... 104 3.14.3. Interpolation - only few points available............................ 106 L0-1c ATBD Version 9 Page 3 of 120 Docnr.: ENV-ATB-DLR-SCIA-0041 Issue : 7A Date : February 7, 2019 3.15.Apply Radiance Response....................................... 108 3.15.1. Sun-normalised radiance.................................... 108 3.16.Quality Flagging............................................. 110 3.16.1. Dead or bad pixel mask..................................... 110 3.16.2. Dark signal quality assessment................................. 110 3.16.3. Wavelength calibration check.................................. 110 3.16.4. Sun glint and Rainbow flag................................... 110 3.16.5. Saturation............................................. 111 3.16.6. Hot pixels............................................. 111 3.16.7. Red Grass............................................ 111 3.16.8. Decontamination flag...................................... 112 3.17.Notes on algorithm description..................................... 113 4. Limitations of the Algorithms 114 A. References 117 A.1. Applicable Documents.......................................... 117 A.2. Literature References.......................................... 117 A.3. Project References............................................ 119 A.4. GOME project documentation and study reports........................... 120 L0-1c ATBD Version 9 Page 4 of 120 List of Figures 2.1. SCIAMACHY optical lay-out. ...................................... 15 2.2. Data flow of science measurements and of calibration measurements. Earth, calibration and monitoring measurements (except darks) are directly transferred to the Level 1b product. For the dark measurements the average is contained in the Level 1b. Calibration parameters are calculated from the calibration measurements in a given orbit and transferred to the calibration