1. SCIAMACHY LoS Mispointing Modelling M. Gottwald & E. Krieg – DLR-IMF - DLR/IFE IUP-IFE, Bremen, 30 November 2006

2. SCIAMACHY Operations Support M. Gottwald & E. Krieg – DLR-IMF, 30 November 2006 page 2 Known LoS Anomalies several measurements display small LoS anomalies auf (known since Commissioning Phase) all of them, except BIAS in limb tangent height, are classified as uncritical approach to use LoS anomalies to understand limb BIAS what can cause LoS anomalies? -extra instrument misalignment (pitch, roll, yaw) -platform attitude misalignment -FOCC planning and scheduling s/w (CFI, SCIACAL) -scanner control s/w -Sun Follower

3. SCIAMACHY Operations Support M. Gottwald & E. Krieg – DLR-IMF, 30 November 2006 page 3 LoS Anomalies – Measured Jumps

4. SCIAMACHY Operations Support M. Gottwald & E. Krieg – DLR-IMF, 30 November 2006 page 4 Coordinate Systems

5. SCIAMACHY Operations Support M. Gottwald & E. Krieg – DLR-IMF, 30 November 2006 page 5 Observed Anomalies (LoS angle) -limb:elevation = -0.016 deg 1 SCIAMACHY is pointing too low tangent heights are too large 1 possibly larger -solar occultation:azimuth = 0.1 deg 2 elevation = -0.04 deg 3 jumps of the ASM and ESM readings when switching to Sun Follower (State 47) 2 at 17.2 km 3 at 100 km -subsolar:azimuth = 0.05 deg 4 elevation = -0.02 deg jump of the ESM readings when switching to Sun Follower and temporal shift of maximum signal (State 53) 4 derived from temporal shift of maximum signal of about 5 BCPS

6. SCIAMACHY Operations Support M. Gottwald & E. Krieg – DLR-IMF, 30 November 2006 page 6 Modelling the Jumps (1) assumption -jumps, temporal shift in subsolar signal and limb BIAS are caused by extra misalignment (known misalignment LoS: pitch = 0.00065°, roll = 0.00167°, yaw = -0.22746°) -azimuth jump in occultation may be a special case (acquisition at 17.2 km = well within the atmosphere) misalignment budget -pitch: p t = p i + p p + p e (t = total misalignment, i = instrument, p = platform, e = extra) -roll: r t = r i + r p + r e -yaw: y t = y i + y p + y e

7. SCIAMACHY Operations Support M. Gottwald & E. Krieg – DLR-IMF, 30 November 2006 page 7 Modelling the Jumps (2) Modelling -derive solar azimuth and elevation for occultation and subsolar viewing using the ENVISAT CFIs -option 1: CFI without any misalignment = reference for subsolar azimuth -option 2: CFI with instrument misalignment = reference for subsolar elevation and occultation elevation -option 3: CFI with instrument misalignment, platform misalignment and variable extra misalignment -combination of option 1/2 and option 3 = simulation of Sun Follower acquisition determine best fit extra misalignment which produces measured jump or time shift

8. SCIAMACHY Operations Support M. Gottwald & E. Krieg – DLR-IMF, 30 November 2006 page 8 Modelling the Jumps (3) option 1 and 2 = scanner control with FOCC prediction option 3 = scanner control with Sun Follower absolute values of azimuth/elevation from SOST-CFIs and FOCC-CFIs are not fully identical (additional corrections at FOCC) difference in absolute values about several 0.01° jumps are relative changes jumps can be modelled with SOST-CFIs

9. SCIAMACHY Operations Support M. Gottwald & E. Krieg – DLR-IMF, 30 November 2006 page 9 Which Jump results from which Misalignment? subsolar elevation roll subsolar azimuth = time of maximum signal yaw and pitch Sun occultation azimuth: not analysed Sun occultation elevation pitch and roll

10. SCIAMACHY Operations Support M. Gottwald & E. Krieg – DLR-IMF, 30 November 2006 page 10 Modelling 20 orbits with state 53 (subsolar) 24 orbits with state 47 (occultation) platform attitude information from AUX_FRA pitch, roll and yaw extra misalignment variations around expected values (limits defined by maximum observed anomalies) search for best fit extra misalignment in pitch, roll and yaw

11. SCIAMACHY Operations Support M. Gottwald & E. Krieg – DLR-IMF, 30 November 2006 page 11 Example: Subsolar Azimuth – Yaw

12. SCIAMACHY Operations Support M. Gottwald & E. Krieg – DLR-IMF, 30 November 2006 page 12 Example: Subsolar Azimuth – Pitch

13. SCIAMACHY Operations Support M. Gottwald & E. Krieg – DLR-IMF, 30 November 2006 page 13 Example: Subsolar Elevation – Roll

14. SCIAMACHY Operations Support M. Gottwald & E. Krieg – DLR-IMF, 30 November 2006 page 14 Solar Occultation Elevation – Assymetric Signal

15. SCIAMACHY Operations Support M. Gottwald & E. Krieg – DLR-IMF, 30 November 2006 page 15 Example: Solar Occultation Elevation – Pitch

16. SCIAMACHY Operations Support M. Gottwald & E. Krieg – DLR-IMF, 30 November 2006 page 16 Example: Solar Occultation Elevation – Roll

17. SCIAMACHY Operations Support M. Gottwald & E. Krieg – DLR-IMF, 30 November 2006 page 17 Example: Solar Occultation Elevation – Yaw

18. SCIAMACHY Operations Support M. Gottwald & E. Krieg – DLR-IMF, 30 November 2006 page 18 Example: Best Fit Roll – Subsolar Elevation (State 53)

19. SCIAMACHY Operations Support M. Gottwald & E. Krieg – DLR-IMF, 30 November 2006 page 19 Subsolar - Results best fit extra misalignments -pitch p e = -0.019° ± 0.004° -roll r e = -0.020° ± 0.004° -yaw y e = 0.000° ± 0.000°

20. SCIAMACHY Operations Support M. Gottwald & E. Krieg – DLR-IMF, 30 November 2006 page 20 Solar Occultation – Results best fit extra misalignments -pitch p e = -0.027° ± 0.002° -roll r e = not sensitive -yaw y e = not sensitive

21. SCIAMACHY Operations Support M. Gottwald & E. Krieg – DLR-IMF, 30 November 2006 page 21 Summary observed LoS anomalies (except azimuth jump in solar occultation) can be explained by extra misalignment: pitch p e = -0.023°, roll r e = -0.020°, yaw y e = 0.000° estimated uncertainties ± 0.002° - 0.003° (equivalent to about 200 m at limb distance) further simulations with smaller p e, r e, y e steps required