1. S2. EUV Irradiance & Calibration

2. February 13-17, 2006 AIA/HMI Science Team Meeting Eparvier - 2 EUV Observations Most of the new missions that make the next 5 years of solar observations look so exciting carry EUV/SXR instruments  Solar-B EIS, XRT  STEREO SECCHI EUVI  GOES SXI, XRS Two of the three SDO instruments are strongly focused on the EUV Calibration of these EUV instruments is essential for a number of reasons:  EVE calibration is important for understanding the effects of irradiance variability on the atmosphere  AIA calibration is important for understanding the thermal structure of the corona  Even scientific investigations that don’t explicitly rely on calibrated EUV observations will benefit from cross-calibration of EUV instruments

3. February 13-17, 2006 AIA/HMI Science Team Meeting Eparvier - 3 Agenda (slightly modified since the announcement was posted) 1. Overview of EVE calibration 2. Overview of AIA-EVE cross-calibration 3. Discussion cross-calibration with other instruments problems priorities procedures Wanted: practical ideas and questions, not necessarily solutions (yet…)

4. EVE and those other instruments on SDO Frank Eparvier LASP / University of Colorado eparvier@lasp.colorado.edu

5. February 13-17, 2006 AIA/HMI Science Team Meeting Eparvier - 5 Reminder: EVE Instrument Overview ESP MEGS B/P MEGS A SAM EOP EEB EVE Resources Power (orbit average)43.9 Watts Mass54.2 kg Data Rate2 kbps (engineering) 7 Mbps (science) Dimensions (L x W x H)99 cm x 61 cm x 36 cm Key Components  EVE Optical Package (EOP) MEGS  MEGS A + SAM  MEGS B + P ESP  EVE Electrical Box (EEB) Processor & Memory Interfaces (1553 & HSB) Power / Heaters / Control CCD power converters ESP power converters Spacecraft Coordinates +X +Y +Z SDO Spacecraft AIA HMI EVE

6. February 13-17, 2006 AIA/HMI Science Team Meeting Eparvier - 6 How does EVE measure the EUV? Multiple EUV Grating Spectrograph (MEGS)  At 0.1 nm resolution MEGS-A: 5-37 nm MEGS-B: 35-105 nm  At 1 nm resolution MEGS-SAM: 0-7 nm  At 10 nm resolution MEGS-Photometers: @ 122 nm  Ly-  Proxy for other H I emissions at 80-102 nm and He I emissions at 45-58 nm EUV Spectrophotometer (ESP)  At 4 nm resolution 17.5, 25.6, 30.4, 36 nm  At 7 nm resolution 0-7 nm (zeroth order) In-flight calibrations from ESP and MEGS-P on daily basis and also annual calibration rocket flights  0.1 1 4 7 10 nm

7. February 13-17, 2006 AIA/HMI Science Team Meeting Eparvier - 7 EVE Science Requirements

8. February 13-17, 2006 AIA/HMI Science Team Meeting Eparvier - 8 EVE Data Products LevelAlgorithm purpose Scientifically Useful DescriptionFile Duration Daily Volume (MB) 0AFast validity check NoTLM consistency/quality checking~1 minute76000 0BAssemble images, detailed data verification NoData checks for CRC and pixel parity, parse data packets, merge image data, separate by science channel and filter wheel position ~1 minute76000 0CSpace WeatherYesQuick-look indices, MEGS-A, MEGS-B, SAM, MEGS-P & ESP 1 minute36 1Apply calibration Yes (SAM, ESP, MEGS-P) Use measurement equations to produce irradiance units 1 hour1095 2Re-grid, extract lines YesBin data to fixed wavelength scale, integrate over emission features with background removal 1 hour1160 3Daily averageYesMerge all component data into daily averages, bin to 0.1 and 1 nm 24 hours0.026

9. February 13-17, 2006 AIA/HMI Science Team Meeting Eparvier - 9 Calibration is a Lifetime Commitment The Calibration Essentials: Understand the Measurement Equation:  Know all the parameters that go into the measurement to irradiance conversion and assess how to best quantify each  Do a thorough error analysis and uncertainty budget Calibrate pre-flight:  Use a standard radiometric EUV source  Primary standards, such as NIST SURF-III source, are preferred (note: SURF beam flux known to <1% for EUV ranges) Track in-flight:  Any instrument changes that will affect results  E.g. detector flat fields, gain changes, temperature effects, background signals, … Re-Calibrate in-flight:  As close after launch as possible (changes since pre-flight calib.)  On a regular basis thereafter in order to track absolute changes  E.g. redundant channels, on-board sources, rocket underflights, proxy models Validate:  With measurements made with other instrumentation  Comparisons with models

10. February 13-17, 2006 AIA/HMI Science Team Meeting Eparvier - 10 MEGS A & B Measurement Equations Where: ESolar spectral irradiance (x,y)Detector pixel location SRaw signal from detector tt Integration time GDetector gain f FF Flatfield correction f Lin Linearity correction C Bkg Background signal C SL Scattered light signal f Image Pixel contribution weighting to slit image Good(x,y)“Good” pixels in slit image A Slit Slit area  Dispersion (bandpass of single detector element) RcRc Responsivity at center of FOV f FOV Pointing within FOV correction f Degrad Degradation correction f 1AU Normalization to 1-AU Wavelength E OS Higher order correction

11. February 13-17, 2006 AIA/HMI Science Team Meeting Eparvier - 11 MEGS-A & B Error Analysis The uncertainties of the various correction factors must be propagated through to determine the accuracy of the measured irradiance (note:  denotes uncertainty in the units of the variable): For bright solar emission features the primary contributors to accuracy are the uncertainties in R C (the responsivity of the instrument) and the f Degrad (degradation correction) For dim solar emissions, other uncertainties dominate, such as the precision of the measurement and the various corrections to the signal

12. February 13-17, 2006 AIA/HMI Science Team Meeting Eparvier - 12 EVE Uncertainty Budget and Verification Matrix Symbol Parameter Description Error Budget Component Level Instrument Level Spacecraft Level On-Orbit Level SSignal34%XXXX tt Integration Time0.02%X GGain1%XX f FF Flatfield2%XXXX f Lin Detector Linearity0.2%XX C Bkg Background20%XXXX C SL Scattered Light20%XXX f Image Slit Image Weight2%XX A Slit Slit Area8%X  Dispersion6%XX RCRC Responsivity at Center 12%XX f FOV FOV Correction10%XX f Degrad Degradation Correction 18%X f 1AU 1-AU Correction0.02%X Wavelength0.2%XX E OS Order Sorting2%XX E Measured Irradiance Product 25%

13. February 13-17, 2006 AIA/HMI Science Team Meeting Eparvier - 13 EVE In-Flight Calibration Activities Continuous Internal Cross-Calibrations:  Overlapping Channels within EVE Daily:  Filter wheel movements (dark, alternate filters)  Flat field lamps for MEGS CCDs (LEDs) Quarterly Maneuvers:  Cruciform Scans: ±150 arcmin in 3 arcmin steps Gives gross FOV changes and locates edges of FOV for relative boresight calibrations to SAM and AIA guide telescope  FOV Maps: ±10 arcmin in 5 arcmin steps (5x5 map) Gives finer FOV changes over nominal FOV pointing area (with margin)  Also get bonus mapping when AIA and HMI require maneuvers (though their mappings are different and not optimized for EVE needs). Annual Rocket Underflights:  Fly prototype instruments on sounding rocket periodically.  Calibrate rocket instruments at NIST before and after flight to transfer best calibration to EVE.

14. Cross-calibration: AIA-EVE, SDO-everybody else

15. February 13-17, 2006 AIA/HMI Science Team Meeting Eparvier - 15 Overview: AIA/EVE cross-calibration Spectral response η(λ) (effective area) of AIA channels determined by component-level calibration measurements  Mirrors (primary determination of bandpass)  Filters  CCDs  System-level effects Estimated BOL relative calibration accuracy for AIA is 15%  Absolute calibration is more difficult  Calibration will change due to contamination, degradation, etc.  Therefore, cross-calibration with EVE is highly desireable First-order cross-calibration procedure:  Use EVE MEGS-A measurements of full-disk solar spectral irradiance to predict a full-disk count rate in each AIA channel  Compare EVE-predicted count rate with AIA’s measured full-disk count rate, and produce a scaling factor for each channel

16. February 13-17, 2006 AIA/HMI Science Team Meeting Eparvier - 16 Refining the Cross-calibration First-order calibration should be easy to implement, but a few questions remain:  What cadence? (yearly? monthly? daily? 10 seconds?)  How do we interpret the resulting scale factors? Contamination? Something else? or is it just an empirical correction, and we don’t worry about it? There are some potential pitfalls to the first-order AIA-EVE cross- calibration:  Field of view  Spectral resolution  Bandpass uncertainty

17. February 13-17, 2006 AIA/HMI Science Team Meeting Eparvier - 17 Field of View AIA field of view is 41 arc- minutes (to edge of CCD) / 46 arc-minutes (vignetting circle)  1.3-2.0 pressure scale heights (at T = 3.0 MK) Based on Yohkoh observations, we estimate that AIA will observe ~ 96 % of the total coronal radiance  Higher fraction for lower- temperature lines  Depends on size and location of particular structures Estimated X-ray radiance at 3 MK as observed by Yohkoh/SXT as function of limb height. Yohkoh/SXT 8 May 1992

18. February 13-17, 2006 AIA/HMI Science Team Meeting Eparvier - 18 Spectral Resolution Spectral resolution of ~ 1 Å results in calibration errors  Less than 1% for longer-wavelength (broad) channels  Up to 25% for 171 and 94 Å Can be corrected by modeling higher-resolution spectrum Simulated full-disk spectrum (10% AR, 90% QS) shown in blue. Blurred with 1 Å FWHM gaussian and binned at 6 pixels/Å in black. Response of AIA 194 channel shown in red. Folding the black spectrum through the red instrument response results in errors of 1- 25% compared to using the blue spectrum.

19. February 13-17, 2006 AIA/HMI Science Team Meeting Eparvier - 19 Bandpass Uncertainty First-order cross-calibration only allows us to correct the overall scale of the AIA response functions Uncertainties in the bandpass shape are more important; can we use EVE to correct those? Measurements of the MSSTA multilayers. This is not data from an AIA telescope, but the illustration of bandpass variations over the mirror surface is relevant. See the poster by R. Soufli et al.

20. February 13-17, 2006 AIA/HMI Science Team Meeting Eparvier - 20 Questions (1 of 3) For AIA-EVE cross-calibration: How often should we perform "first-order" calibration? What data products are necessary for this cross-calibration? What sort of operational coordination is necessary? Coordination with rocket underflights? How do we interpret the resulting scaling factors?  contamination?  something else?  not at all? How do we deal with the field-of-view discrepancy? How do we use EVE to correct the bandpass shape of the AIA? To what extent will cross-calibrations rely on spectral modeling? What improvements in spectral modeling can be made to enhance calibration accuracy? Can AIA-EVE cross-calibration be used to constrain Fe abundance? What role can DEM extraction from AIA play in cross-calibration, and extending the spectral range of EVE?

21. February 13-17, 2006 AIA/HMI Science Team Meeting Eparvier - 21 Questions (2 of 3) For EIS-AIA-EVE inter-calibration: How does EIS-AIA cross-calibration feed back into AIA-EVE cross- calibration? Is it possible to get full-disk spectra with EIS? If not, how do we cross-calibrate with EVE? If so, how can we coordinate this cross-calibration? Will it be possible to cross-calirbate EIS with the LASP rocket this year? For XRT-EVE cross-calibration: Can the EVE SAM and ESP be used to cross-calibrate with XRT? Would this be useful? What sort of coordination is necessary? How often should this be done? etc. Can XRT and AIA be cross-calibrated? How? (Using DEM extraction?)

22. February 13-17, 2006 AIA/HMI Science Team Meeting Eparvier - 22 Questions (3 of 3) Are TRACE and EIT going to be observing during SDO? If so, how do we cross-calibrate with AIA? If not, how do we establish continuity between the AIA dataset and the EIT/TRACE datasets? How important is this cross-calibration? For AIA, how important is it to have accurate: Absolute calibration? Relative calibration (channel-to-channel)? Bandpass shape calibration?

23. February 13-17, 2006 AIA/HMI Science Team Meeting Eparvier - 23 Backup Slides

24. February 13-17, 2006 AIA/HMI Science Team Meeting Eparvier - 24 EVE and AIA Inter-Calibrations EVE spectra can be convolved with AIA bandpasses and compared with integrated images to transfer an absolute irradiance calibration from EVE to AIA.  What’s needed for this transfer? AIA bandpasses (!) AIA image conversion to irradiance EVE irradiances  Can EVE be used to track changing AIA bandpasses?  Probably, but how the bleep do we do that?  Logistical Questions: Do AIA and EVE integrations need to be coincident? Do special data products need to be made for inter-calibrations? How frequently should comparisons be done? Are there special calibration activities on-orbit that should be planned? In conjunction with rocket underflights?

25. February 13-17, 2006 AIA/HMI Science Team Meeting Eparvier - 25 Action Items from EVE Science Workshop (Nov, 2005)

26. February 13-17, 2006 AIA/HMI Science Team Meeting Eparvier - 26 Comments from EVE Science Workshop (Nov, 2005)