SOLSTICE I and II: Ultraviolet Variability. Marty Snow, Bill McClintock, Tom Woods, and Gary Rottman Laboratory for Atmospheric and Space Physics

Transcription

1 SOLSTICE I and II: Ultraviolet Variability Marty Snow, Bill McClintock, Tom Woods, and Gary Rottman Laboratory for Atmospheric and Space Physics

2 Outline SOLSTICE I and II Measurement Equations Individual terms in Measurement Eqns Degradation analysis Stars FOV A/B transfer Uncertainty in Variability SSI Workshop: SOLSTICE 2

3 What is SOLSTICE? SOLar-STellar Irradiance Comparison Experiment. SOLSTICE I UARS FUV 0.1 nm MUV 0.2 nm Vis ( N channel) SOLSTICE II SORCE FUV 0.1 nm MUV 0.1 nm Two redundant units Data Versions: V18 CDHF V22 LASP Data Version V11 (current) SSI Workshop: SOLSTICE 3

4 What is SOLSTICE (2)? SOLSTICE I Grating Spectrometer PMT detectors MUV interference filter SOLSTICE II Grating Spectrometer PMT detectors MUV neutral density filters (removable) SSI Workshop: SOLSTICE 4

5 Measurement Equations SSI Workshop: SOLSTICE 5

6 Dead Time Measured preflight Inflight cannot be separated from filter transmission, but combined T and N are unchanged. February 2012 SSI Workshop: SOLSTICE 6

7 Stray and Scattered Light Measured inflight by rotating grating to put an out-of-band wavelength on detector. Signal is then only from dark and stray light. Stray light correction has not yet been implemented in data processing. It is a small correction. February 2012 SSI Workshop: SOLSTICE 7

8 Dark Current February 2012 SSI Workshop: SOLSTICE 8

9 Responsivity SSI Workshop: SOLSTICE 9

10 Responsivity Uncertainty McClintock et al Snow et al (in press) February 2012 SSI Workshop: SOLSTICE 10

11 Wavelength Scale Level 2 spectra Simple Gaussian

12 Degradation Correction Repeat Observation of Stars measures absolute changes in system for stellar field of view. Relative change of center of FOV to edge needed to more precisely measure solar mode degradation (SORCE MUV ONLY) Transfer degradation from B to A. February 2012 SSI Workshop: SOLSTICE 12

13 B to A Transfer January 2006 entrance aperture mechanism anomaly on SOLSTICE A Commanded to solar mode and has remained in that mode ever since Stellar and FOV corrections are made on SOLSTICE B, then A measurements are corrected to coincide with B. SSI Workshop Introduction 13

14 UARS Stellar Observations SSI Workshop: SOLSTICE 14

15 Ensemble of Stars SSI Workshop: SOLSTICE 15

16 Ensemble of Stars one day hit anomalies change solar/stellar FOV correction Tape recorder failure 11/99. No more stars. Change to closed loop tracking on the Sun. (star tracker failure) 2/02 SSI Workshop: SOLSTICE 16

17 SORCE Stellar Uncertainty in stellar correction is about 1% Eclipse observations reduced to preserve battery. February 2012 SSI Workshop: SOLSTICE 17

18 Solar/Stellar Field of View SSI Workshop: SOLSTICE 18

19 FOV Degradation Stellar image illuminates much more pristine area on both M1 and Grating, so total change in stellar irradiances show only a diluted version of solar degradation. Weekly alignment scans measure change across FOV as the solar image is scanned across the optics. Measurement of change of top of haystack gives indication of depth of hole being burned in region of optics exposed to sun.

20 Preflight Calibration at Only One Wavelength

21 Normalized Haystack

22 Wavelength Shift

23 Normalized and Shifted Data

24 Fit for wavelength 189 nm

25 Fit for wavelength 204 nm

26 Overlap Correction to FOV The ratio of the center of the FOV to the point on the side captures the depth of the burn-in hole only if the solar images don t overlap. Due to vignetting when too far off-axis, we use a point 0.27 degrees away from the center, so the two images overlap. Therefore the correction on the previous series of plots underestimates the degradation by the fractional area overlap of the two images.

27 FOV Uncertainty Random errors in each measurement less than 1%. Systematic error is larger since FOV was not well-calibrated before launch. Measurement at 4 wavelengths since beginning of mission, but 4 additional wavelengths only since September Total uncertainty in this correction over 9 years of mission is probably 2%. SSI Workshop: SOLSTICE 27

28 Why FOV correction? Shouldn t stars capture all the degradation? If degradation on optics is on M1, the ratio between solar and stellar is ~9x. If degradation is on grating, the ratio is more like ~3x. Measurement seems better than guessing at solar/stellar scaling factor. SSI Workshop: SOLSTICE 28

29 UARS FOV Correction The illumination of the optics is not identical in solar and stellar modes. The solar image burns a hole in the center of the FOV. The depth of this hole can be measured with an alignment scan and corrected. This correction is applied on top of the stellar degradation correction. SSI Workshop: SOLSTICE 29

30 A/B Comparison Experiments Simultaneous measurements of Sun with both A and B (both MUV and FUV). Performed Weekly until late 2009, then performed Daily until present. Used to transfer DEG correction from B to A since A can no longer make stellar measurements.

31 Time Series at 180.5nm

32 A/B at 200nm

33 A/B 220 nm

34 A/B 240 nm

35 A/B 290 nm

36 A/B Summary Solstice version 10 inadvertently smoothed this function over wavelength, thus introducing the unusual wavelength dependence of the variability.

37 Uncertainty in A/B Current functional fit is only accurate to 1-2%. Next data version will have improved functional form. February 2012 SSI Workshop: SOLSTICE 37

38 Degradation Uncertainty The three components of the MUV degradation correction have the following uncertainties in their magnitudes over the nine year mission: Stellar 1% (absolute loss of signal over large FOV) FOV 2% (relative loss of signal between center and edge of the FOV) A/B 2% (factor required to bring A into agreement with the fully-corrected B measurements) These three components are independent sources of error, so the total uncertainty is the sum in quadrature. In the worst case, the SOLSTICE degradation is uncertain by 3%. February 2012 SSI Workshop: SOLSTICE 38

39 SOLSTICE MUV Variability 3% February 2012 SSI Workshop: SOLSTICE 39

40 Backup Slides February 2012 SSI Workshop: SOLSTICE 40

41 SOLSTICE I in 2003 FUV: Nearly full mission has been reprocessed at LASP and is consistent with prior CDHF processing. MUV: LASP data processing system cannot fully reproduce CDHF processing yet, therefore no MUV data exists (yet) after September 19, 2006 SSI Workshop: SOLSTICE 41

42 SOLSTICE I Validation Average irradiance is taken from Woods et al paper. SSI Workshop: SOLSTICE 42

43 SOLSTICE I Validation Average irradiance is taken from Woods et al paper. SSI Workshop: SOLSTICE 43

44 Preflight Calibration of SOLSTICE II Full details are in McClintock, Snow, & Woods (2005). September 19, 2006 SSI Workshop: SOLSTICE 44

45 Comparison to White Dwarfs SSI Workshop: SOLSTICE 45

46 MUV Comparison September 19, 2006 SSI Workshop: SOLSTICE 46

47 MUV with Uncertainty September 19, 2006 SSI Workshop: SOLSTICE 47

48 UARS MUV Data Availability Unfortunately, the existing data processing system needs to be revised before we can produce irradiances after the end of September 19, 2006 SSI Workshop: SOLSTICE 48

49 FUV Ratio of SOLSTICEs Seems too good to be true. September 19, 2006 SSI Workshop Introduction 49

50 FUV Compared to both UARS September 19, 2006 SSI Workshop Introduction 50

51 Expected FUV Difference September 19, 2006 SSI Workshop: SOLSTICE 51

52 FUV Time Series - Lyα September 19, 2006 SSI Workshop Introduction 52

53 The Good September 19, 2006 SSI Workshop Introduction 53

54 The Good Ratio flat Both SOLSTICES are consistent relative to SUSIM September 19, 2006 SSI Workshop Introduction 54

55 The Bad September 19, 2006 SSI Workshop Introduction 55

56 The Bad UARS Ratio diverges SORCE SOLSTICE has same trend as SUSIM, although large calibration difference. Quiet Sun irradiances may or may not be comparable. September 19, 2006 SSI Workshop Introduction 56

57 The Ugly September 19, 2006 SSI Workshop Introduction 57

58 The Ugly Ratio diverged in 1992, then flattened out, then rose for a few years, then flattened out again. SORCE SOLSTICE trend matches SUSIM. UARS SOLSTICE now matches SORCE, but Quiet Sun irradiances make no sense. September 19, 2006 SSI Workshop Introduction 58

59 Summary MUV calibration differences seem to be consistent with previous validation. SOLSTICE II agrees with SUSIM at the 2% level. Agrees with SOLSTICE I at the 7% level. FUV degradation issues for both SUSIM and SOLSTICE may complicate understanding of calibration. Agreement is still within stated uncertainties. September 19, 2006 SSI Workshop: SOLSTICE 59