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GOME-2 Degradation Assessment Team Meeting #2

GOME-2 Degradation Assessment Team Meeting #2. Rűdiger Lang, Rose Munro, Yakov Livschitz, Antoine Lacan, Richard Dyer EUMETSAT. Reference sources used for degradation analysis Section 3.1. The sun reflected by a diffuser (solar mean reference (SMR) measurement mode)

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GOME-2 Degradation Assessment Team Meeting #2

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  1. GOME-2 Degradation Assessment Team Meeting #2 Rűdiger Lang, Rose Munro, Yakov Livschitz, Antoine Lacan, Richard Dyer EUMETSAT

  2. Reference sources used for degradation analysisSection 3.1 • The sun reflected by a diffuser (solar mean reference (SMR) measurement mode) • The white light source (WLS) • An ETALON residual effect derived from WLS measurements • The spectral light source (SLS) • The SLS Over Diffuser (SLSDif) • Moon Calibrations (Not analysed yet) • Earth measurements over stable areas –e.g. Sahara • The LEDs which are inside the optical path, in the vicinity of the detectors

  3. Calibration steps applied per monitoring sourceSection 3, Table 1. Assessment team EUM summary report

  4. Light source incident angles on mirror MAX EXT, q=14.3 NADIR q=49.3 MIN EXT , q=-73.3 DRK, q=0 SLS, q=34.2 SMR, q=40.0 WLS, q=44.6

  5. GOME-2 Long-term throughput changes until June 2010 LED, SMR, WLS, Section 3.1 283 nm Channel 1 420 nm Channel 3 Reprocessed signals PPF 4.0 until June 2010 relative to February 2007

  6. GOME-2 Long-term throughput changes until June 2010 LED, SMR, WLS, Section 3.1 541 nm Channel 1 745 nm Channel 3 Reprocessed signals PPF 4.0 until June 2010 relative to February 2007

  7. Summary degradation rate for selected wavlength Table 3-2,Section 3

  8. Long-term residual etalon changes Figure 3-6,Section 3 Etalon changes relative to on-ground situation and with high-pass filter (FFT) applied. This residual etalon is used for correction of calibrated level 1b radiances.

  9. Long-term degradation FPA vs PMD Figure 3-7,Section 3 FPA-SMR smoothed (black line) with PMD spectral response function.

  10. Yet another mechanism (1) E-mail 9 September to Assessment team Following the 2nd throughput test LED on the one hand and WLS or SMR on the other hand degrade roughly speaking in the same way and independent of wavelength! Before the 2nd throughput test the large residual degradation between LED and SMR or WLS was strongly wavelength dependent. Still there is a small but non‐negligible additional signal step function also in the LED to be observed following the second throughput test in all channels (see plots on LED channel dependent differences before and after 2nd throughput test as already distributed and subject to discussion at the kick‐off meeting). 283 nm ch1 420 nm ch2

  11. Yet another mechanism (1) SMR vs LED Normalised to 29th September 2009 – Post 2nd Throughput Test No etalon correction between 313 (ch1) and 316.7 (ch2) nm Following the 2nd throughput test LED on the one hand and WLS or SMR on the other hand degrade roughly speaking in the same way and independent of wavelength! Before the 2nd throughput test the large residual degradation between LED and SMR or WLS was strongly wavelength dependent. No etalon correction between 392 (ch2) and 417 (ch3) nm Don’t forget that we expect some scan mirror degradation contribution to SMR!

  12. Yet another mechanism (1) SMR vs LED Normalised to 29th September 2009 – Post 2nd Throughput Test Don’t forget that we expect some scan mirror contribution! Following the 2nd throughput test LED on the one hand and WLS or SMR on the other hand degrade roughly speaking in the same way and independent of wavelength! Before the 2nd throughput test the large residual degradation between LED and SMR or WLS was strongly wavelength dependent.

  13. Yet another mechanism (1) SMR vs LED Normalised to 29th September 2009 – Post 2nd Throughput Test Don’t forget that we expect some scan mirror contribution! Following the 2nd throughput test LED on the one hand and WLS or SMR on the other hand degrade roughly speaking in the same way and independent of wavelength! Before the 2nd throughput test the large residual degradation between LED and SMR or WLS was strongly wavelength dependent.

  14. Yet another mechanism (1) SMR vs LED Normalised to 29th September 2009 – Post 2nd Throughput Test Don’t forget that we expect some scan mirror contribution! Following the 2nd throughput test LED on the one hand and WLS or SMR on the other hand degrade roughly speaking in the same way and independent of wavelength! Before the 2nd throughput test the large residual degradation between LED and SMR or WLS was strongly wavelength dependent.

  15. Yet another mechanism (1) SMR vs LED Normalised to 29th September 2009 – Post 2nd Throughput Test Don’t forget that we expect some scan mirror contribution! Following the 2nd throughput test LED on the one hand and WLS or SMR on the other hand degrade roughly speaking in the same way and independent of wavelength! Before the 2nd throughput test the large residual degradation between LED and SMR or WLS was strongly wavelength dependent.

  16. Yet another mechanism (2) Proposal for a mechanism There is a long‐term continuous degradation of the detectors as observed by the bulk of the long‐term LED degradation, which is broadly speaking independent of wavelength (therefore maybe not linked to contaminants of the typical sort but maybe more related to the detector itself). Before the 2nd throughput test there is an additional, heavily wavelength dependent, degradation of probably some contaminant (not to forget the scan mirror contribution), which builds up (continuous increase in throughput loss) until the 2nd throughput test. After this test this obstruction is suddenly not increasing anymore for FPA channels, i.e. it is stable but having created an additional loss in a short time (proposal: exhausted reservoir by out‐gassing theory). A) happens at the detector itself (or its electronics, etc..) whereas B) happens in between the LEDs and the detector (because of (III)). So, e.g., on the detector window or the lenses between LED, and detector window.

  17. Yet another mechanism (2) Proposal for a mechanism For the PMDs, looking over the full period of time, they already showed much more of an (slow) onset of saturation in the degradation rate dynamics (i.e. more than the FPAs having steeper gradients at an earlier stage than the FPA but slowing down later on and even before the 2nd throughput test. Looking at the results with the removed LED contribution for channel 5 and 6 as attached it looks like there is also an earlier onset of an stabilization with regard to an dynamic built up of contaminants and what remains is the LED degradation rate at detector level. This is also why things between PMD and FPA tend to look more "consistent" after the 2nd throughput test, since the PMD part of contaminants have exhausted their built‐up already to a large extend before the test, whereas the FPA got down to the PMD throughput level only after the test, exhausting their reservoir (whatever it might be). There is not much of a varying additional scan‐mirror contribution left after the 2nd throughput test, though there was probably a significant varying contribution of the scan mirror beforehand (note, that this is not to say there is no scan‐mirror contribution to the low signal levels in the UV left at all, but instead that this contribution has not changed much in the period from October 2009 to June 2010). This does not yet explain the hysteresis effect in any detail but leaves both, a dynamic source of contamination and the direct detector effect (since we see the hysteresis for both LED and SMR/WLS) in the picture, which may be responsible for such an effect.

  18. 2nd throughput test analysis Improved plots as requested by assessment team FPA-SMR smoothed (black line) with PMD spectral response function.

  19. 2nd throughput test analysis Improved plots as requested by assessment team

  20. 2nd throughput test analysis Improved plots as requested by assessment team

  21. GOME-2 / AVHRR radiance co-location GOME-2 channel 3 and 4 and AVHRR channel 1 data AVHRR ch1 response function GOME-2 Ch:4 (Band 6) 1024 measurements GOME-2 Ch:3 (Band 5) 1024 measurements Detector pixel read-out sequence direction GOME-2 channel 3 Detector pixel read-out sequence direction GOME-2 channel 4 Read-out of all 1024 detector pixel takes 1024*45,78 ms = 46.875 ms introducing “spatial aliasing” (~2km across-track)

  22. AVHRR/3 Validation using GOME-2Long-term radiance inter-comparison Courtesy of Barry Latter et al. (2009) Preliminary results: AVHRR ch1 9 to 12% lower than GOME-2 ch4 reflectance. GOME-2 contribution <3%. So far no significant long-term trend!

  23. Stray-light analysis As requested by assessment team Not yet done! Proposal: Use channel 1, first 100 detector pixel (203 to 240 nm) Use SMR level 0 measurements, dark-offset subtracted and normalised Look at the long-term development (2007 to present)

  24. Post Metop-A launch operations schedule Schedule and events list after launch Not yet done! Proposal: Support by Michael Eisinger.

  25. Etalon data Schedule and events list after launch Not yet done! TBD Etalon data can be provided by: Providing un-calibrated or calibrated WLS data Provide ETALON residual (correction) as processed by level 1 processor and specified in PGS 6.1, Section 5.2.18 Any other ETALON related data

  26. Basic signatures using Feb2010 analysis Basic signatures using Feb2010 analysis

  27. GOME-2 Long-term throughput changes Solar Mean Reference (SMR) spectrum Reprocessed signals PPF 4.0 until February 2010 relative to February 2007

  28. GOME-2 Long-term throughput changes Solar Mean Reference (SMR) spectrum - PMDs PMD-P PMD-S Reprocessed signals PPF 4.0 until February 2010 relative to February 2007

  29. GOME-2 Long-term throughput changes Solar Mean Reference (SMR) spectrum - PMDs PMD-P/PMD-S Reprocessed signals PPF 4.0 until February 2010 relative to February 2007

  30. GOME-2 Long-term throughput changes White Light Source (WLS) spectrum Reprocessed signals PPF 4.0 until February 2010 relative to February 2007

  31. GOME-2 Long-term throughput changes White Light Source (WLS) spectrum PMD-P PMD-S Reprocessed signals PPF 4.0 until February 2010 relative to February 2007

  32. GOME-2 Long-term throughput changes ETALON correction evolution Reprocessed signals PPF 4.0 until Februrary 2010 ETALON values are not normalised to the beginning of the mission period

  33. GOME-2 Long-term throughput changes ETALON spectrum PMD-P PMD-S Reprocessed signals PPF 4.0 until Februrary 2010 ETALON values are not normalised to the beginning of the mission period

  34. GOME-2 Long-term throughput changes All calibration sources 311 nm 541 nm Reprocessed signals PPF 4.0 until February 2010 relative to February 2007

  35. GOME-2 Long-term throughput changes SLS vs. SLS over diffuser Reprocessed signals PPF 4.0 until February 2010 relative to February 2007

  36. Earthshine degradation Sahara – 330nm – relative to mean of 2007 • Earthshine Sahara • Normalised to 2007 • Every 2nd scanner angle position is used (coloured solid lines) • Solar Mean Reference (black dashed line) • Low outliers are due to interfering narrow scan

  37. Earthshine degradation Sahara – 745nm – relative to mean of 2007 • Earthshine Sahara • Normalised to 2007 • Every 2nd scanner angle position is used (coloured solid lines) • Solar Mean Reference (black dashed line) • Low outliers are due to interfering narrow scan

  38. Earthshine degradation Sahara – 330nm – relative to mean of 2007 • Earthshine Sahara • Normalised to 2007 • Every 2nd scanner angle position is shown

  39. Earthshine degradation Sahara – 330nm – relative to mean of 2007 – relative to nadir • Earthshine Sahara • Normalised to 2007 • Normalised to nadir position (read-out nr 12) • Every 2nd scanner angle position is shown

  40. Reflectivity degradation Sahara – 330nm – relative to mean of 2007 – relative to nadir • Reflectivity Sahara • Normalised to 2007 • Normalised to nadir position (read-out nr 12) • Every 2nd scanner angle position is shown

  41. Earthshine degradation rate Sahara – 330nm – relative to mean of 2007 • Earthshine Sahara • Normalised to 2007 • Every 2nd scanner angle position is shown • Solar Mean Reference degradation rate in red (solar incident angle is eq. to scanner position 17)

  42. Reflectivity degradation rate Sahara – 330nm – relative to mean of 2007 • Reflectivity Sahara • Normalised to 2007 • Every 2nd scanner angle position is shown

  43. Differential Reflectivity degradation rate Sahara – 340/380nm – relative to mean of 2007 • Differential Reflectivity Sahara • Normalised to 2007 • Every 2nd scanner angle position is shown

  44. GOME-2 Long-term dark signals Electronic offset and detector leakage Time series to be updated... Band 1A averaged Band 2B averaged

  45. GOME-2 Long-term dark signals Electronic offset and detector leakage Time series to be updated... Band 3 averaged Band 4 averaged

  46. GOME-2 Long-term dark signals Detector read-out noise [BU/s] from dark measurements Time series to be updated... Band 1A averaged Band 2B averaged

  47. GOME-2 Long-term dark signals Detector read-out noise [BU/s] from dark measurements Band 3 averaged Time series to be updated... Co-adding turned off in band 3 Band 4 averaged Timeline change in March 2009 Co-adding turned on in band 3

  48. Degradation Assessment – Switch-Off (1) During nominal operations both FPAs and PMDs are degrading, broadly speaking, in the same way. Whatever mechanism for degradation that we propose should be applicable to both the FPAs and the PMDs. Summary of Switch-Off Behaviour • FPAs during instrument switch-off show an increase in throughput when the detectors are warm followed by a decrease after the detectors are cooled, but without returning to the level before the switch-off. • Throughput only returns to previous levels following a somewhat exponential curve, after a period of about two weeks. This is the only circumstance where we do not have a near immediate response in the FPAs to change in detector temperature. • In this case the instrument is presumably in approximate thermal equilibrium after the switch-off.

  49. Degradation Assessment – 1st Throughput Test (1) Summary of Events • Aim – to raise the set point temperature of the FPAs in 5K intervals until a target temperature of 265K was reached • Test carried out successfully however with some notable deviations • The target temperature of 265 K for FPAs could not be reached • The highest temperatures reached were oscillating (with loss of active cooling) between 257 and 260 K with open dale resistor relay • the higher temperatures at switch-off periods are reached because of closed dale resistor relay • PMD signals for SUN were lost because of erroneous timeline (wrong PMD transfer mode)

  50. Degradation Assessment – 1st Throughput Test (2) With open dale resistor relay the environment temperatures are lower (between 257 and 261K) than during switch-off periods (~265 K) during which the closed dale resistor warms the back-plate of the detectors in order to prevent them falling below 250 K. Similar behaviour for other FPA detectors

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