1 st post launch SCIAMACHY calibration & Verification Meeting L1b Astrium Friedrichshafen – Germany 24 July 2002 First Level 1b Spectral Calibration analysis

2 Level 1b Spectral Calibration analysis: content The Spectral Calibration philosophy The Iecf Spectral Calibration Algorithm Related Verification Tasks: orbit behaviour Analysis specifics First results Other Spectral Calibration Verification Tasks Recommendations

3 The Spectral Calibration Philosophy Objective : to assign a wavelength to each individual SCIA detector pixel during the flight. Method : the relation between pixel index and wavelength is described by a 4 th order polynomial: To derive a set of calibration coefficients two calibration sources, the SLS and the sun, are analysed. Stability : due to ageing of the instrument, the wavelength parameters needs to be updated on a regular basis. Iecf, Instrument Engineering and Calibration Facility, guarantees long term stability of scientific measurements.

4 The Iecf Spectral Calibration Algorithm Task : to determine coefficients of the 4 th order polynomial for each channel as function of the orbital regions. Input: Level 1b Newly Calculated Spectral ADS Method : for each polynomial coefficient, given by the Spectral ADS as a function of orbital phase, a harmonic fit has to be performed in order to parameterise the orbital dependence. The coefficients values are then computed for a set of 12 fixed orbital phases:

5 Related verification Task: orbit behaviour L : Number of orbital regions for spectral calibration L : Orbit region dependency Due to the instrument’s thermal environment along the orbit, the spectral calibration can be expected to show orbital dependency. Therefore SLS measurements shall be executed along the entire orbit to investigate whether the number of measurements and the number of orbital regions are sufficient and the orbit phase boundaries are chosen properly.

6 Analysis specifics and overview Level 1b product: SCI_NL__0PNPDK _182502_ _00056_01613_0129.N1 Orbits: 1613 States: 10 SLS States (predefined State_ID 59 ), on 87 total States Channel 1 : variation long the orbit is close or less to 1/100 of a pixel Channel 2 : not analysed due to erroneous key-data set used by the Level 0 to 1b processor Channels 3, 4, 5 and 6 : variation long the orbit is close or less to 1/100 of a pixel Channel 7 and 8 : not analysed for no in-flight dark current correction of the the raw lamp spectrum

First Results: Orbit dependency for Channel 1 The algorithm performs correctly the harmonic fit of the coefficients. … but is this the best approach to the Spectral Calibration?

First Results: Orbit dependency for Channel 3 The algorithm performs correctly the harmonic fit of the coefficients. … but is this the best approach to the Spectral Calibration?

First Results: Orbit dependency for Channel 4 The algorithm performs correctly the harmonic fit of the coefficients. … but is this the best approach to the Spectral Calibration?

First Results: Orbit dependency for Channel 5 The algorithm performs correctly the harmonic fit of the coefficients. … but is this the best approach to the Spectral Calibration?

First Results: Orbit dependency for Channel 6 The algorithm performs correctly the harmonic fit of the coefficients. … but is this the best approach to the Spectral Calibration?

First Analysis: the harmonic fit approach for Channel 1 Orbit 1613 Maximum variation long the orbit: E-03 nm or 0.01 of a pixel

First Analysis: the harmonic fit approach for Channel 3 Orbit 1613 Maximum variation long the orbit: E-02 nm or of a pixel

First Analysis: the harmonic fit approach for Channel 4 Orbit 1613 Maximum variation long the orbit: E-03 nm or of a pixel

First Analysis: the harmonic fit approach for Channel 5 Orbit 1613 Maximum variation long the orbit: E-02 nm or 0.07 of a pixel

First Analysis: the harmonic fit approach for Channel 6 Orbit 1613 Maximum variation long the orbit: E-02nm or of a pixel

First analysis: variation on the input for Channel 1 Coefficient average long the orbit as reference Maximum variation long the orbit from average: E-03 nm or of a pixel Maximum variation long the orbit from fit: E-03 nm or 0.01 of a pixel

First analysis: variation on the input for Channel 3 Coefficient average long the orbit as reference Maximum variation long the orbit from average: E-03 nm or of a pixel Maximum variation long the orbit from fit: E-02 nm or of a pixel

First analysis: variation on the input for Channel 4 Coefficient average long the orbit as reference Maximum variation long the orbit from average: E-03 nm or of a pixel Maximum variation long the orbit from fit: E-03 nm or of a pixel

First analysis: variation on the input for Channel 5 Coefficient average long the orbit as reference Maximum variation long the orbit from average: E-03 nm or of a pixel Maximum variation long the orbit: E-02 nm or 0.07 of a pixel

First analysis: variation on the input for Channel 6 Coefficient average long the orbit as reference Maximum variation long the orbit from average: E-03 nm or of a pixel Maximum variation long the orbit: E-02nm or of a pixel

22 First Analysis: Summary

23 All Spectral Cal Related Verification Tasks L Number of orbital regions for spectral calibration L Wavelength calibration - selected line list not changes L Slit function parameters unchanged L Verification of precise basis for spectral calibration L Verification of selected lines for calibration L Verify orbit region dependency L Verify whether SLS or Fraunhofer calibration shall be the baseline L : Wavelength calibration differences monitoring

24 Level 1b Spectral Calibration analysis: Recommendations The approach averaging the coefficients from the Level 1b seems to give better results Fit based on a lower order polynomial shall be investigated …